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Influence of swimming activity on sodium and water balance in the rainbow trout (Salmo gairdneri). Wood, Christopher Michael 1971

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THE INFLUENCE OF SWIMMING ACTIVITY ON SODIUM AND WATER BALANCE IN THE RAINBOW TROUT (SALMO GAIRDNERI) by CHRIS M. WOOD B . S c , U n i v e r s i t y o f B r i t i s h Columbia, 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n t h e Department o f Zoology We a c c e p t t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA January, 19 71 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i I m e n t o f the r e q u i r e m e n t s f o r an advanced deg ree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t he L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r ag ree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t he Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s , t t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Depar tment o f Z o o l o g y The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, Canada January 27th, 1971 ABSTRACT The permeability of the t e l e o s t b r a n c h i a l exchanger to oxygen and carbon dioxide i s apparently enhanced during exercise by increased blood p e r f u s i o n of t h i n walled high surface area pathways i n the g i l l s , the second-ary lamellae. However t h i s augmented permeability to r e s p i r a t o r y gases may w e l l be accompanied by unfavourable elevations of water and e l e c t r o l y t e f l u x e s between i n t e r n a l and external environments. The object of the present study was to i n v e s t i g a t e the e f f e c t of imposed swimming a c t i v i t y on sodium and water r e g u l a t i o n i n the fresh water adapted rainbow trout, Salmo g a i r d n e r i . Radiotracer methods were used to measure u n i d i r e c t i o n a l components of b r a n c h i a l sodium exchange i n f i s h at r e s t , during one hour of swimming, and during one hour of recovery from t h i s exercise c o n d i t i o n . Sodium fluxes during extended exercise (up to 8 hours) were q u a n t i f i e d by s i m i l a r techniques i n a second s e r i e s of experiments. These long term swimming t r i a l s provided f l u x r a t e data.at a wide range of external sodium concentrations; a n a l y s i s of these r e s u l t s helped to elucidate the r e l a t i v e importance of d i f f e r e n t mech-anisms o f branchial sodium t r a n s f e r i n the rainbow t r o u t . F i n a l l y , deter-minations of urine flows and body weight changes under c o n t r o l l e d exercise conditions i n a swimming respirometer permitted an a n a l y s i s of water r e g u l -a t i o n and d i r e c t measurement of r e n a l e l e c t r o l y t e losses during a c t i v i t y . The sodium uptake system of Salmo g a i r d n e r i i n the present study had an extremely high a f f i n i t y f o r the i o n ( h a l f s a t u r a t i o n concentration = . 0 1 4 mEq Na +/L). Both u n i d i r e c t i o n a l f l u x rates at the g i l l s of rainbow trout were greater than those reported f o r any other fresh water t e l e o s t of comparable s i z e , despite external sodium l e v e l s much lower than those used by other workers. The presence of an exchange d i f f u s i o n mechanism f o r sodium i n the trout g i l l was strongly i n d i c a t e d but not confirmed.. Branchial trans-port o f the e l e c t r o l y t e was t e n t a t i v e l y divided i n t o a l a r g e exchange d i f f -r usion component, and smaller a c t i v e i n f l u x and simple d i f f u s i o n a l e f f l u x elements. I n r e s t i n g animals, b r a n c h i a l sodium i n f l u x and e f f l u x rates were equal. However short term a c t i v i t y ( 1 hour) was associated with a 70% increase i n e f f l u x o f sodium across the g i l l s , c r e a t i n g a net sodium d e f i c i t . This e f f e c t was q u i c k l y reversed (within 5 minutes) upon the termination of swimming. As i n f l u x d i d not vary, these phenomena probably represented changes i n the simple d i f f u s i o n a l e f f l u x component without disturbance of c a r r i e r mediated sodium transport mechanisms. Branchial water entry was a l s o g r e a t l y elevated at the s t a r t of exercise. These r e s u l t s were i n t e r -preted i n terms of augmented passive movements of sodium and water caused by increased blood perfusion of the high permeability r e s p i r a t o r y pathways of the g i l l s during swimming. The extended exercise experiments revealed that the high sodium e f f l u x r a t e o f the f i r s t hour of a c t i v i t y diminished, during the second hour, and had returned to r e s t i n g l e v e l s by the t h i r d and subsequent hours of swimming; i n f l u x again remained unchanged. The i n i t i a l high branchial water entry was a l s o apparently c u r t a i l e d , but over a shorter time i n t e r v a l (15 - 60 minutes a f t e r the onset of a c t i v i t y ) . These reductions i n b r a n c h i a l permeability to water and sodium were in t e r p r e t e d as compensations to de-crease the osmotic penalty of exercise. As water entry through the g i l l s declined, urinary output was aug-mented; an elevated r e n a l sodium l o s s accompanied the d i u r e s i s . However sodium e f f l u x through the kidney remained small r e l a t i v e to the e f f l u x of t h i s e l e c t r o l y t e through the g i l l s . A f i n a l equilibrium between branchial entry and r e n a l excretion of water was attained, but at a higher turnover r a t e than during r e s t . Before t h i s balance, however, urinary e l i m i n a t i o n had over-compensated f o r the i n i t i a l water gain. The r e s u l t i n g net water i i i d e f i c i t reduced the blood space below r e s t i n g volume, causing a s l i g h t i n -crease i n plasma sodium l e v e l s despite enhanced br a n c h i a l and r e n a l losses of the i o n . An ischemia of "white" muscle may a l s o have accompanied the haemoconcentration. In summary, the r e s u l t s i n d i c a t e d that an i n i t i a l osmoregulatory disturbance was associated with a r e d i s t r i b u t i o n of blood flow through the g i l l s during swimming, but that both b r a n c h i a l hydromineral permeability and the f u n c t i o n i n g of other systems could be modified by compensations necessary to maintain sodium and water balance during extended exercise. i v TABLE OF CONTENTS Page ABSTRACT • i TABLE OF CONTENTS i v LIST OF TABLES ' v i LIST OF FIGURES v i i i ACKNOWLEDGEMENTS x i GENERAL INTRODUCTION 1 SECTION I - THE EFFECT OF EXERCISE (ONE HOUR) ON SODIUM BALANCE. INTRODUCTION I 14 METHODS I 18 1. E x p e r i m e n t a l /inimals 18 2. O p e r a t i n g Procedures and C a n n u l a t i o n s 19 — - 3. E x p e r i m e n t a l - S y s t e m - -2"4 ~ 4. A n a l y t i c a l Procedures 33 5. C a l c u l a t i o n s 36 6. P r e s e n t a t i o n o f Data 40 RESULTS AND DISCUSSION I 43 A . The E f f e c t o f Chasi n g on V e n t i l a t o r y and C a r d i o v a s c u l a r Parameters 43 B. The E f f e c t o f E x e r c i s e on B r a n c h i a l Sodium f l u x e s 54 C. The E f f e c t o f E x e r c i s e on Sodium and Water D i s t r i b u t i o n 74 SUMMARY I 95 SECTION I I - THE EFFECT OF EXTENDED EXERCISE ON SODIUM BALANCE. INTRODUCTION I I 97 METHODS I I 101 1. E x p e r i m e n t a l Animals 101 2. O p e r a t i n g Procedures and C a n n u l a t i o n s 101 3. E x p e r i m e n t a l System 101 4. A n a l y t i c a l P rocedures 106 5. C a l c u l a t i o n s 106 RESULTS AND DISCUSSION I I 110 A . Sodium F l u x Rates d u r i n g Extended E x e r c i s e 110 V Page B. The C o n c e n t r a t i o n Dependence o f B r a n c h i a l Sodium F l u x e s 129 SUMMARY I I 143 SECTION I I I - THE EFFECT OF EXERCISE ON WATER BALANCE INTRODUCTION I I I 146 METHODS I I I 149 I . U r i n e Flow v e r s u s Oxygen Consumption Experiments 149 1. O p e r a t i n g Procedure and C a n n u l a t i o n s 149 2. E x p e r i m e n t a l System 150 3. A n a l y t i c a l P r o c e d u r e s 154 I I . Weight Change v e r s u s Swimming D u r a t i o n Experiments 157 RESULTS AND DISCUSSION I I I 159 SUMMARY I I I 186 GENERAL DISCUSSION — — ' - —188 LITERATURE CITED 203 VI L I S T OF TABLES Page I. V e n t i l a t o r y a n d c a r d i o v a s c u l a r r e s p o n s e s o f t r o u t d u r i n g r e s t i n g , a c t i v e , a n d r e c o v e r y e x p e r i m e n t s , e x p r e s s e d i n t e r m s o f mean "% r o u t i n e " v a l u e s . 44 I I . P h y s i c a l d i m e n s i o n s o f t r o u t i n t h e t h r e e e x p e r i -m e n t a l g r o u p s o f S e c t i o n I . 56 I I I . A v e r a g e b r a n c h i a l s o d i u m f l u x r a t e s o v e r t h e e x -p e r i m e n t a l p e r i o d s o f S e c t i o n I i n r e s t i n g , a c t i v e , a n d r e c o v e r y g r o u p s o f t r o u t . 58 I V . Summary o f b r a n c h i a l u n i d i r e c t i o n a l f l u x r a t e s i n f r e s h w a t e r t e l e o s t s . 71 V. E f f e c t i v e b l o o d p o o l s c a l c u l a t e d f r o m h e m a t o c r i t c h a n g e s i n r e s t i n g , a c t i v e , a n d r e c o v e r y g r o u p s o f . t r o u t . 77 V I . T e r m i n a l c o n c e n t r a t i o n s o f s o d i u m a n d w a t e r i n p l a s m a a n d t i s s u e s o f r e s t i n g , a c t i v e , a n d r e c o v e r y g r o u p s o f t r o u t . 82 V I I . M e a s u r e s o f i n t e r n a l d i s t r i b u t i o n o f i n f l u x e d s o d i u m i n r e s t i n g , a c t i v e , a n d r e c o v e r y g r o u p s o f t r o u t . 92 V I I I . B a l a n c e s h e e t o f f a t e o f i n f l u x e c ^ s o d i u m a t 60 m i n u t e s a f t e r i n t r o d u c t i o n o f Na i n r e s t i n g , a c t i v e a n d r e c o v e r y g r o u p s o f t r o u t . 92 IX . P h y s i c a l d i m e n s i o n s o f t r o u t i n t h e t h r e e t r e a t -ment g r o u p s o f S e c t i o n I I . I l l X. U r i n a r y s o d i u m e f f l u x r a t e s o f shams e s t i m a t e d b y s u b t r a c t i o n o f t h e mean b r a n c h i a l e f f l u x r a t e s o f t h e u r i n a r y b l o c k a g e g r o u p f r o m t h e mean v/hole a n i m a l e f f l u x r a t e s o f t h e shams. 121 X I . C o m p a r i s o n o f c a l c u l a t e d r e n a l s o d i u m e f f l u x r a t e s d u r i n g swimming i n shams w i t h r e p o r t e d d i r e c t m e a s u r e m e n t s o f maximum u r i n a r y s o d i u m d i s c h a r g e i n S almo g a i r d n e r i . 122 X I I . T e r m i n a l m e a s u r e m e n t s o f i n t e r n a l s o d i u m and w a t e r l e v e l s , r a d i o s o d i u m s p a c e s , h e m a t o c r i t s , and w e i g h t c h a n g e s o v e r t h e e x p e r i m e n t a l p e r i o d i n n o r m a l , sham, a n d u r i n a r y b l o c k a g e t r e a t m e n t g r o u p s . 124 X I I I . Summary o f maximum s o d i u m i n f l u x r a t e s ( F i ( m a x ) ) a n d h a l f s a t u r a t i o n c o n c e n t r a t i o n s ( K s ) f o r s o d i u m u p t a k e s y s t e m s i n a v a r i e t y o f a n i m a l s . 133 v i i P age X I V . C a l c u l a t e d c o n t r i b u t i o n o f d i f f e r e n t m e c h a n i s m s t o t o t a l b r a n c h i a l s o d i u m e x c h a n g e i n u r i n a r y b l o c k a g e t r o u t a s s u m i n g a l l i n f l u x - e f f l u x l i n k a g e t o be c a u s e d b y e x c h a n g e d i f f u s i o n . 140 XV. P h y s i c a l d i m e n s i o n s o f t h e t r o u t u s e d i n S e c t i o n I I I . 164 X V I . R e s t i n g s t a t e u r i n e f l o w s , o x y g e n u p t a k e s , a n d v e n t i l a t i o n r a t e s f o r 5 t r o u t i n m e t a b o l i s m b o x e s . 164 X V I I . T a i l b e a t f r e q u e n c i e s , v e n t i l a t i o n r a t e s , a n d o x y g e n c o n s u m p t i o n s d u r i n g e a c h h o u r o f t h e i m p o s e d swimming r e g i m e o f S e c t i o n I I I . 166 X V I I I . U r i n e f l o w s a n d c o n c e n t r a t i o n s o f 4 c a t i o n s d u r i n g e a c h h o u r o f t h e i m p o s e d swimming r e g i m e o f S e c t i o n I I I . 180 ! v i i i L IST OF FIGURES F a c i n g Page 1 A drawing o f the l o c a t i o n and s i z e o f the b u c c a l and d o r s a l a o r t i c cannulae used i n S e c t i o n I . 20 2 Drawings o f the c o n s t r u c t i o n , placement, and f i x a t i o n o f the u r i n a r y c a t h e t e r used i n S e c t i o n I . 22 3 A drawing o f the e x p e r i m e n t a l system used i n S e c t i o n I . 26 4 T y p i c a l p r e s s u r e r e c o r d i n g s from the d o r s a l a o r t a and b u c c a l c a v i t y o f a rainbow t r o u t d u r i n g r e s t , c h a s i n g , and r e c o v e r y . 45 5 Changes i n h e a r t r a t e under r e s t i n g , a c t i v e , and r e c o v e r y c o n d i t i o n s o f S e c t i o n I . 46 6 Changes i n a r e a mean d o r s a l a o r t i c b l o o d p r e s s u r e under r e s t i n g , a c t i v e , and r e c o v e r y c o n d i t i o n s _ _of S e c t i o n I . - - _ _ - 49 -7 Changes i n v e n t i l a t i o n r a t e under r e s t i n g , a c t i v e , and r e c o v e r y c o n d i t i o n s o f S e c t i o n I . 51 8 Changes i n b u c c a l p r e s s u r e amplitude under r e s t i n g , a c t i v e , and r e c o v e r y c o n d i t i o n s o f S e c t i o n I . 52 9 B r a n c h i a l sodium f l u x r a t e s over c o n s e c u t i v e i n t e r v a l s o f the e x p e r i m e n t a l p e r i o d s i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . 57 10 B r a n c h i a l sodium net f l u x r a t e s over c o n s e c u t i v e i n t e r v a l s o f the e x p e r i m e n t a l p e r i o d f o r the r e c o v e r y treatment group. 61 11 Mean u r i n e flow r a t e s i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . 73 12 Changes i n h e m a t o c r i t i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . 75 13 Changes i n plasma sodium c o n c e n t r a t i o n s over the e x p e r i m e n t a l p e r i o d s i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . 80 14 The e v o l u t i o n o f the r a d i o s o d i u m space w i t h time i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . 85 15 The e v o l u t i o n w i t h time o f the c o n c e n t r a t i o n i n plasma o f sodium t r a n s p o r t e d from the e x t e r n a l en-vironment i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . 86 i x F a c i n g Page 16 A d r a w i n g o f t h e r e v o l v i n g chamber u s e d f o r l o n g t e r m e x e r c i s e o f t r o u t i n S e c t i o n I I . 103 17 R e s u l t s o f a t y p i c a l e x p e r i m e n t o f S e c t i o n I I i l l u s t r a t i n g t h e m e thod o f d a t a a n a l y s i s a p p l i e d . 112 18 R e s u l t s o f two e x p e r i m e n t s o f S e c t i o n I I demon-s t r a t i n g : (a) f l u x r a t e d a t a f r o m a t r o u t w h i c h swam c o n t i n u o u s l y f o r 8 h o u r s , (b) f l u x r a t e d a t a f r o m a t r o u t w h i c h was i n a c t i v e f o r most o f t h e e x p e r i m e n t a l p e r i o d . 114 19 S o d i u m f l u x r a t e s , m e a s u r e d a t e x t e r n a l c o n c e n -t r a t i o n s g r e a t e r t h a n 0.8 u g / m l , u n d e r d i f f e r e n t e x e r c i s e c o n d i t i o n s i n n o r m a l , sham, and u r i n a r y b l o c k a g e t r o u t . 116 20 The r e l a t i o n s h i p b e t w e e n b r a n c h i a l s o d i u m i n f l u x r a t e a n d e x t e r n a l s o d i u m c o n c e n t r a t i o n . 130 21 C o m p a r i s o n o f t h e c o n c e n t r a t i o n d e p e n d e n c e o f b r a n c h i a l s o d i u m i n f l u x i n t h e r a i n b o w t r o u t w i t h t h a t r e p o r t e d i n f o u r _ o t h e r f r e s h w a t e r f i s h . _ 1 3 5 ^ -22 The - r e l a t i o n s h i p b e t w e e n b r a n c h i a l s o d i u m e f f l u x r a t e a n d e x t e r n a l s o d i u m c o n c e n t r a t i o n . 138 23 A d i a g r a m o f t h e swimming r e s p i r o m e t e r u s e d i n S e c t i o n I I I . 152 24 The d e c l i n e i n u r i n e f l o w w i t h t i m e a f t e r MS 222 a n a e s t h e s i a a n d c a t h e t e r i z a t i o n i n 5 t r o u t . 162 25 The d e c l i n e i n v e n t i l a t i o n r a t e a n d o x y g e n c o n -s u m p t i o n w i t h t i m e a f t e r MS 222 a n a e s t h e s i a a n d c a t h e t e r i z a t i o n i n 3 t r o u t . 163 26 S i m u l t a n e o u s c h a n g e s i n u r i n e f l o w s a n d o x y g e n u p t a k e s d u r i n g t h e c o n t i n u o u s i m p o s e d swimming r e g i m e o f S e c t i o n I I I . 168 2 7 The r e l a t i o n s h i p b e t w e e n o x y g e n c o n s u m p t i o n and u r i n e f l o w i n 3 t r o u t s u b j e c t e d t o a c o n t i n u o u s swimming r e g i m e . 170 28 T h r e e e x a m p l e s o f t h e phenomenon i n w h i c h an e x t r e m e d i u r e s i s a t t h e s t a r t o f e x e r c i s e was d r a s t i c a l l y r e d u c e d d u r i n g c o n t i n u e d swimming. 171 29 C h a n g e s i n b o d y w e i g h t o f t r o u t i n r e s p o n s e t o v a r i o u s e x e r c i s e d u r a t i o n s a n d i n r e s p o n s e t o t h e h a n d l i n g n e c e s s a r y f o r t h e d e t e r m i n a t i o n s a l o n e . 174 30 A tentative model of water balance in the rainbow trout during exercise. 177 X Facing Page 31 Concentration changes of 4 cations i n urine from a s i n g l e trout over the continuous swimming regime of Section I I I . 182 32 The not renal excretion of 4 cations during the continuous swimming regime of Section I I I . 185 33 Models . . i l l u s t r a t i n g sodium and water balance i n the rainbow trout at r e s t , s h o r t l y a f t e r the onset of a c t i v i t y , and a f t e r prolonged exercise. 189 x i ACKNOWLEDGEMENTS I wish t o thank my s u p e r v i s o r , Dr. Dav i d R a n d a l l , b o t h f o r h i s e x c e l l e n t guidance throughout the c o u r s e o f the stu d y and f o r making my p a s t few y e a r s a t the U n i v e r s i t y o f B r i t i s h Columbia a v e r y e n j o y a b l e e x p e r i e n c e . I am a l s o i n d e b t e d t o Dr. J . E . P h i l l i p s , Dr. A.M.Perks, and Mr. F r e d McConnell f o r t h e i r generous s u p p l y o f a d v i c e and equipment. My s i n c e r e a p p r e c i a t i o n a l s o goes t o the f o l l o w i n g p e r s o n s : M i s s Ora Johannsson, f o r her i n v a l u a b l e h e l p , e s p e c i a l l y i n use o f computing f a c i l i t i e s ; m y . c o l l e a g u e s , Mr. John D a v i s , Mr. E r i c Watts, -Dr. Dan Toews-j-and Dr. Jim Cameron f o r t h e i r c o n t i n u e d i n t e r e s t and a s s i s t a n c e ; and my mother, Mrs.0.A.Wood, who c h e e r f u l l y performed the l a b o r i o u s t a s k o f t y p i n g the m a n u s c r i p t . P e r s o n a l f i n a n c i a l s u p p o r t was p r o v i d e d by s c h o l a r -s h i p s from the N a t i o n a l Research C o u n c i l o f Canada and the McLean F r a s e r fund, and a s m a l l t e a c h i n g a s s i s t a n t s h i p from U.B.C. The r e s e a r c h was funded by g r a n t s from the N a t i o n a l Research C o u n c i l and the B r i t i s h Columbia Hear t F o u n d a t i o n . GENERAL INTRODUCTION I n a l l h i g h e r o r g a n i s m s , t h e r e s p i r a t o r y s u r f a c e r e p r e s e n t s t h e p o i n t o f c l o s e s t p r o x i m i t y b e t w e e n t h e i n t e r n a l a n d e x t e r n a l e n v i r o n m e n t s . As s u c h , t h e s t r u c t u r e o f t h i s a r e a p r e s e n t s m i n i m a l r e s i s t a n c e t o t h e d i f f u s i o n o f o x y g e n a n d c a r b o n d i o x i d e down a c t i v i t y g r a d i e n t s , w h i l e i t s s i t u -a t i o n r e l a t i v e t o t h e f l o w s o f e x c h a n g i n g f l u i d s o p t i m i z e s c o n d i t i o n s f o r g a s t r a n s f e r . However a s y s t e m d e s i g n e d f o r t h e e f f e c t i v e d i f f u s i o n a l t r a n s p o r t o f one m o l e c u l a r s p e c i e s may e q u a l l y w e l l s e r v e t h e f l u x o f a n o t h e r m o l e c u l a r s p e c i e s i f a p p r o p r i a t e g r a d i e n t s f o r t h e l a t t e r e x i s t a c r o s s t h e s u r -f a c e o f t h e e x c h a n g e r . The movement o f s u b s t a n c e s a c r o s s t h e e x c h a n g e a r e a w h i c h a r e . e x t r a n e o u s t o i t s r e s p i r a t o r y p u r p o s e may b e d e t r i m e n t a l t o t h e o r g a n i s m ; t h e v a l i d i t y o f t h i s s t a t e -ment i s e a s i l y d e m o n s t r a t e d b y t h e e f f e c t o f a r t i f i c i a l e l e v a t i o n t o a b n o r m a l l e v e l s o f a common component o f t h e v e n t i l a t o r y medium ( e . g . c a r b o n m o n o x i d e ) . U n d e r n o r m a l c i r c u m s t a n c e s , s i g n i f i c a n t g r a d i e n t s f o r r e a d i l y d i f f u s i b l e c o n s t i t u e n t s o f t h e i n t e r n a l o r e x t e r n a l m e d i a may e x i s t a c r o s s t h e r e s p i r a t o r y s u r f a c e . F o r some s u c h s u b s t a n c e s , t h e r e s u l t a n t f l u x e s may be s u f f i c i e n t l y u n f a v o u r -a b l e t o t h e . a n i m a l t o n e c e s s i t a t e l i m i t a t i o n s o f t h e e x c h a n g e c a p a c i t y o f t h e r e s p i r a t o r y s y s t e m . The e v o l u t i o n o f t h e l u n g i n a i r - b r e a t h i n g t e t r a p o d s c a n be v i e w e d as a g r o s s e x a m p l e o f t h i s phenomenon. L o s s o f b o d y w a t e r i s t h e most s e r i o u s d i f f u s i o n a l p r o b l e m c o n c o m i t a n t w i t h t h e u s e o f a i r a s a r e s p i r a t o r y medium. The d e v e l o p m e n t o f an i n t e r n a l g a s 2 e x c h a n g e r e f f e c t i v e l y c o n t r o l l e d d e h y d r a t i o n b u t n e c e s s i -t a t e d a s s u m p t i o n o f t h e r e l a t i v e l y i n e f f i c i e n t t i d a l mode o f v e n t i l a t i o n , a l i m i t a t i o n w h i c h t h e o r g a n i s m c o u l d a f f o r d b e c a u s e o f t h e h i g h o x y g e n c a p a c i t y , l a r g e g a s e o u s d i f f u s i o n c o e f f i c i e n t s , a n d l o w d e n s i t y o f a i r . A somewhat a n a l a g o u s s i t u a t i o n a p p l i e s i n w a t e r b r e a t h i n g v e r t e b r a t e s w h e re d i f f e r e n t i a l c o n c e n t r a t i o n s o f i o n s a n d w a t e r b e t w e e n i n t e r n a l a n d e x t e r n a l m i l i e u x c a u s e d e l e t -e r i o u s h y d r o m i n e r a i e x c h a n g e a c r o s s t h e r e s p i r a t o r y e p i t h e l i u m . T h i s o s m o t i c d e f i c i t c a n n o t be p r e v e n t e d t h r o u g h m o d i f i c a t i o n o f t h e mode o f v e n t i l a t i o n ; o n l y t h e p o s s e s s i o n o f an e x c h a n g e r w i t h a s m a l l f u n c t i o n a l " s i z e " o r p e r m e a b i l i t y w i l l e f f e c t i v e l y c o n t r o l s a l t a n d w a t e r f l u x e s . T h u s t h e r e s p i r a t o r y s u r f a c e a r e a p e r u n i t b o dy w e i g h t i n t e l e o s t s ( H ughes,1966) i s o n l y 1/2 - 1/7 t h a t i n mammals ( H i l d e b r a n d t and Young,1965) w h i l e d i f f u s i o n d i s t a n c e s b e t w e e n medium and b l o o d a r e up t o s i x t i m e s g r e a t e r i n t h e g i l l ( N e w s t e a d , 1 9 6 7 ) t h a n i n t h e l u n g ( H i l d e b r a n d t a n d Y o u n g , 1 9 6 5 ) . However e v e n t h e p o s s e s s i o n o f a r e l a t i v e l y s m a l l e x c h a n g e r h a s n o t , b y i t s e l f , b e e n s u f f i c i e n t t o f u l l y c o n t r o l e l e c t r o l y t e a n d w a t e r movements. T o l e r a n c e o f t h e o s m o t i c d e f i c i t h a s b e e n e f f e c t e d t h r o u g h t h e d e v e l o p m e n t o f s e c o n d a r y c o m p e n s a t o r y m e c h a n i s m s w i t h f u r t h e r e n e r g e t i c demand. A c t i v e t r a n s p o r t a p p a r a t u s on t h e g i l l t o pump i o n s i n o p p o s i t i o n t o t h e i r n e t d i f f u s i o n a l f l u x e s , e f f i c i e n t r e n a l d e v i c e s t o e l i m i n a t e w a t e r g a i n e d f r o m a h y p o - o s m o t i c e n v i r o n -ment, a n d i n t e s t i n a l a b s o r p t i o n c a p a b i l i t i e s t o r e p l a c e w a t e r l o s t t o a h y p e r o s m o t i c e x t e r n a l medium h a v e a l l b e e n n e c e s s i -t a t e d b y t h e u s e o f an a q u e o u s r e s p i r a t o r y medium. C o m p a r i s o n s b e t w e e n f i s h i n n o r m a l an d i s o s m o t i c e n v i r o n m e n t s h a v e r e v e a l e d t h a t t h e s e o s m o r e g u l a t o r y r e q u i r e m e n t s may a c c o u n t f o r up t o 30% o f t h e o r g a n i s m ' s t o t a l o x y g e n c o n s u m p t i o n (Rao,1968; F a r m e r a n d B e a m i s h , 1 9 6 9 ) . The l o w m e t a b o l i c r a t e o f t e l e o s t t i s s u e may t h u s be a t l e a s t p a r t i a l l y a t t r i b u t a b l e t o t h e o s m o r e g u l a t o r y p e n a l t y i n v o l v e d i n b r e a t h i n g an aqueous medium. The a b o v e c o n s i d e r a t i o n s i n d i c a t e t h a t t h e a n a t o m i c a l d e v e l o p m e n t o f t h e t e l e o s t r e s p i r a t o r y e p i t h e l i u m i s l i m i t e d by t h e l e v e l o f i o n a n d w a t e r e x c h a n g e w h i c h t h e a n i m a l c a n t o l e r a t e . Y e t i t i s known t h a t f i s h c a n e l e v a t e t h e i r o x y g e n c o n s u m p t i o n t e n t i m e s o r more t h r o u g h i n c r e a s e s i n v e n t i l a t i o n , c a r d i a c o u t p u t , a n d t h e o x y g e n . t r a n s f e r f a c t o r o f t h e g i l l s ( R a n d a l l e t a l _ . , 1 9 6 7 ) . The l a t t e r e x p r e s s i o n r e f e r s t o u n i t s o f g a s t r a n s f e r r e d p e r u n i t g r a d i e n t a n d w i l l be a f f e c t e d b y t h e r e s i s t a n c e t o d i f f u s i o n o f t h e e n t i r e e x c h a n g e r . T h u s i t w o u l d a p p e a r t h a t t e l e o s t s h a v e t h e c a p a c i t y t o v a r y t h e e f f -e c t i v e " s i z e " o f t h e r e s p i r a t o r y e p i t h e l i u m w i t h i n t h e s t r u c t -u r a l l i m i t s d e s c r i b e d p r e v i o u s l y . The c o n c e p t t h a t , a t any one t i m e , t h i s b r a n c h i a l p e r m e a b i l i t y must r e p r e s e n t a d y n a m i c c o m p r o m i s e b e t w e e n r e s p i r a t o r y demand and o s m o t i c r e g u l a t i o n h a s b e e n a d v a n c e d r e p e a t e d l y ( S t e e n and K r u y s s e , 1 9 6 4 ; R a n d a l l e t a l . , 1 9 6 7 ; T a y l o r e t a l . , 1 9 6 8 ; K i r s c h n e r , 1 9 6 9 ; R a n d a l l , 1 9 7 0 a) The o r i g i n a n d d e v e l o p m e n t o f t h i s h y p o t h e s i s may be t r a c e d t o p h y s i c a l , s t r u c t u r a l , and p h y s i o l o g i c a l o b s e r v a t i o n s on t h e t e l e o s t g i l l . T h e f u n d a m e n t a l u n i t o f b r a n c h i a l s t r u c t u r e i s t h e f i l a m e n t ; two rows o f t h e s e f l a t t e n e d t a p e r s a r e b o r n e on a h e m i b r a n c h . P a r a l l e l rows o f l e a f - l i k e , l a c u n a r s e c o n d a r y l a m e l l a e a r e s i t u a t e d on b o t h s i d e s o f e a c h f i l a m e n t . The 4 l a m e l l a e o f a d j a c e n t f i l a m e n t s s p a t i a l l y i n t e r l o c k t o p r o d u c e a s i e v e - l i k e s t r u c t u r e ( s e e H u g h e s , 1 9 6 6 ) ; t h a t p o r t i o n o f t h e v e n t i l a t o r y w a t e r f l o w w h i c h i s i n v o l v e d i n g a s , i o n , o r w a t e r e x c h a n g e p a s s e s t h r o u g h t h e p o r e s o f t h e s i e v e , t h u s c o n t a c t i n g t h e w a l l s o f t h e l a m e l l a e a n d t h e b o d y o f t h e f i l a -m ent. The d i r e c t i o n o f b l o o d f l o w i n t h e r e s p i r a t o r y l e a f l e t s i s i n o p p o s i t i o n t o t h a t o f w a t e r f l o w , t h u s c r e a t i n g an e f f i c i e n t c o u n t e r - c u r r e n t e x c h a n g e s y s t e m (Hughes an d S h e l t o n , 1 9 6 2 ) . S u b s t a n c e s w h i c h move b e t w e e n t h e i n t e r n a l a n d e x t e r -n a l m i l i e u x a r e b r o u g h t t o t h e e x c h a n g e s u r f a c e b y t h e b u l k f l o w s o f b l o o d and w a t e r . The n e t p a s s i v e m i g r a t i o n ( i . e . b y d i f f u s i o n o r o s m o s i s ) o f any s p e c i e s o f p a r t i c l e a c r o s s t h e r e s p i r a t o r y e p i t h e l i u m may be d e s c r i b e d b y t h e r e l a t i o n : w here F = n e t f l u x C i = a c t i v i t y o f p a r t i c l e s i n s i d e F = AD ( C i - Co) Co = a c t i v i t y o f p a r t i c l e s o u t s i d e X A = s u r f a c e a r e a a c r o s s w h i c h movement o c c u r s X = d i s t a n c e t h r o u g h w h i c h move-ment o c c u r s D = c o e f f i c i e n t D i s a m e a s u r e d c o e f f i c i e n t q u a n t i f y i n g t h e r e s i s t a n c e t o movement o f t h e p a r t i c u l a r s u b s t a n c e o v e r t h e d i s t a n c e i m p l i -c a t e d . F o r t h e p u r p o s e o f t h i s d i s c u s s i o n , C i and Co must b e c o n s i d e r e d as c o n s t a n t s d e t e r m i n e d b y t h e n a t u r e o f t h e e x t e r n a l e n v i r o n m e n t an d t h e h o m e o s t a t i c demands o f t h e i n t e r -n a l m i l i e u . However v a r i a t i o n s i n t h e p a r a m e t e r s A, D, a n d X may a l l be f e a s i b l e m e c h a n i s m s f o r r e g u l a t i n g t h e e f f e c t i v e b r a n c h i a l " s i z e " . I n o r d e r t o e x a m i n e how e a c h o f t h e s e c o m p o n e n t s may o p e r a t e , i t i s f i r s t n e c e s s a r y t o c o n s i d e r p r e s e n t i n f o r m a t i o n on t h e anatomy a n d p h y s i o l o g y o f b r a n c h i a l t i s s u e . 5 S t u d i e s on i s o l a t e d p e r f u s e d g i l l p r e p a r a t i o n s h a v e d e m o n s t r a t e d t h a t t h e v a s c u l a r r e s i s t a n c e o f t h e b r a n c h i a l c a p i l l a r y n e t w o r k i s s e n s i t i v e t o s e v e r a l v a s o - a c t i v e a g e n t s (Krawkow,1913; K e y s an d Bateman,1932; O s t l u n d a n d F a n g e , 1 9 6 2 ; R a n d a l l e t a l . , 1 9 6 9 ; R i c h a r d s and Fromra,1969,1970); i n p a r t -i c u l a r c a t e c h o l a m i n e s i n c r e a s e , w h i l e a c e t y l c h o l i n e d e c r e a s e s , t h e r a t e o f f l u i d f l o w t h r o u g h t h e p r e p a r a t i o n . D a t a c o l l e c t e d on t h e i n v i v o e f f e c t s o f t h e s e d r u g s h a s s o f a r b e e n l i m i t e d t o t h e i r a c t i o n s on b l o o d p r e s s u r e , e f f e c t s w h i c h a r e u l t i m a t e l y d e p e n d e n t on c a r d i a c o u t p u t a n d t h e r e s i s t a n c e o f t h e e n t i r e c i r c u l a t o r y s y s t e m , and t h e r e f o r e d i f f i c u l t t o i n t e r p r e t w i t h r e s p e c t t o t h e b r a n c h i a l a r e a a l o n e ( M o t t , 1 9 5 1 ; S t e e n a n d K r u y s s e , 1 9 6 4 ; R a n d a l l and S t e v e n s , 1 9 6 7 ; K i r s c h n e r , 1 9 6 9 ) . However, a t l e a s t f o r a d r e n a l i n e and n o r a d r e n a l i n e , t h e r e s u l t s seem t o a g r e e q u a l i t a t i v e l y w i t h t h e o b s e r v a t i o n s on e x c i s e d p r e p a r a t i o n s . M e d i a t i o n o f t h e s e r e s i s t a n c e s h i f t s i s p r o b a b l y e f f e c t e d b y t h e d o u b l e n a t u r e o f t h e c i r c u l a t i o n i n a t y p i c a l g i l l f i l a m e n t ( R i e s s , 1 8 8 1 ) . S t e e n a n d K r u y s s e (1964) h a v e d e m o n s t r a t e d t h a t a t any one t i m e , b l o o d c a n f l o w f r o m t h e a f f e r e n t t o e f f e r e n t f i l a m e n t a l a r t e r i e s e i t h e r t h r o u g h t h e l a c u n a e o f t h e r e s p i r a t o r y l a m e l l a e o r t h r o u g h t h e b o d y o f t h e f i l a m e n t . I n t h e l a t t e r p a t h w a y , p a s s a g e t o t h e e x c u r r e n t a r t e r y i s p o s s i b l e v i a e i t h e r a l a r g e c o n n e c t i v e t i s s u e s p a c e , t h e c e n t r a l " l y m p h a t i c " s i n u s , o r d i r e c t v a s c u l a r c o n n e c t i o n s a t t h e t i p o f t h e f i l a m e n t . M i c r o s c o p i c e x a m i n a t i o n o f s i n g l e e x c i s e d f i l a m e n t s i n d i c a t e d t h a t i n t h e p r e s e n c e o f a d r e n a l i n e , b l o o d moved s o l e l y t h r o u g h t h e l a m e l l a e ; c o n v e r s e l y a d d i t i o n o f a c e t y l c h o l i n e r e s t r i c t e d f l o w e n t i r e l y t o t h e 6 f i l a m e n t a l r o u t e s . More s o p h i s t i c a t e d s t u d i e s ( R i c h a r d s a n d Fromm,1969, 1970) s u p p o r t e d t h e s e o b s e r v a t i o n s b u t r e v e a l e d t h a t t h e d i v i s i o n b e t w e e n l a m e l l a r and f i l a m e n t a l f l o w was a g r a d e d r a t h e r t h a n an a b s o l u t e r e s p o n s e . T h e s e w o r k e r s c o n c l u d e d t h a t s i g n i f i c a n t a d j u s t m e n t s i n b r a n c h i a l p e r f u s i o n p a t t e r n s a r e m e d i a t e d a d r e n e r g i c a l l y w i t h m i n o r t o n i c c h o l i n -e r g i c c o n t r o l . The f a c t o r s o p e r a t i n g t h e s e v a s c u l a r s h u n t s c o n s t i t u t e , h o w e v e r , a m a t t e r o f c o n s i d e r a b l e d i s p u t e a t p r e s e n t . The c o l l a g e n b e a r i n g p i l l a r c e l l s w h i c h f o r m t h e s k e l e t o n o f t h e r e s p i r a t o r y l a m e l l a e h a v e l o n g b e e n s u s p e c t e d o f p o s s e s s i n g i n n a t e c o n t r a c t i l i t y ( P l e h n , 1 9 0 1 ) . The d i s c o v e r y , t h r o u g h e l e c t r o n m i c r o s c o p y , o f c y t o p l a s m i c f i l a m e n t s i n t h e s e c e l l s s i m i l a r t o t h e m y o f i l a m e n t s o f s mooth m u s c l e ( R h o d i n , 1 9 6.4 ; H ughes and G r i m s t o n e , 1 9 6 5 ; N e w s t e a d , 1 9 6 7 ) h a s l e n t c o n s i d e r a b l e s u p p o r t t o t h i s b e l i e f . T h i s f i n d i n g , i n c o m b i n a t i o n w i t h an a p p a r e n t a b s e n c e o f s t r u c t u r a l c o n t r a c t i l e e l e m e n t s i n a f f e r e n t o r e f f e r e n t a r t e r i a l w a l l s , h a s l e d some w o r k e r s t o p r o p o s e t h a t b l o o d d i s t r i b u t i o n i s r e g u l a t e d e x c l u s i v e l y b y t h e p i l l a r c e l l s ( H ughes an d G r i m s t o n e , 1 9 6 5 ; N e w s t e a d , 1 9 6 7 ; D a t t a M u n s h i and S i n g h , 1 9 6 8 ) . C h a n g e s i n t h e c r o s s - s e c t i o n a l a r e a o f t h e r e s p i r a t o r y l a c u n a e t h r o u g h c o n t r a c t i o n o r e x p a n s i o n o f t h e s k e l e t a l c e l l s w o u l d p r e s u m a b l y a f f e c t t h e r e s i s t a n c e o f a l l t h r e e s h u n t • p a t h w a y s . However R i c h a r d s a n d Fromm (1969) r e j e c t t h i s t h e o r y on t h e g r o u n d s t h a t , i f t h e l a m e l l a r v o l u m e i s t h e o n l y r h e o s t a t i n t h e c i r c u i t o f t h r e e p a r a l l e l f l o w r o u t e s , t h e n i t must be c a p a b l e o f an a l m o s t i n f i n i t e r a n g e o f r e s i s t a n c e t o a c c o u n t f o r t h e o b s e r v e d v a r i a t i o n s i n b l o o d d i s t r i b u t i o n among t h e s h u n t s . I n a d d i t i o n t h e y h a v e demon-7 s t r a t e d m u s c u l a r e l e m e n t s o r s i m i l a r t h i c k e n i n g s i n t h e w a l l s o f l a m e l l a r a n d c e n t r a l s i n u s v e s s e l s , a n d a r g u e t h a t t h e c o n t r o l o f g i l l b l o o d d i s t r i b u t i o n i n v o l v e s some c o m b i n a t i o n o f a f f e r e n t and e f f e r e n t l a m e l l a r a r t e r i o l e s and e f f e r e n t s i n u s v e s s e l s . R e c e n t i n f r a r e d p h o t o g r a p h i c o b s e r v a t i o n s on l i v e g i l l t i s s u e s i n t h i s l a b o r a t o r y ( D a v i s a n d R a n d a l l - p e r s o n a l c o m m u n i c a t i o n ) r e v e a l t h a t l a m e l l a e l o c a t e d d i s t a l t o t h e h e m i b r a n c h on a f i l a m e n t a r e n o t n o r m a l l y f i l l e d w i t h b l o o d b u t may be o p e n e d b y i n t r a v a s c u l a r a d m i n i s t r a t i o n o f a d r e n a l i n e . C i r c u m s t a n t i a l e v i d e n c e i n d i c a t e s t h a t t h i s d i s t r i b u t i o n o f b l o o d may be r e l a t e d i n p a r t t o b l o o d p r e s s u r e e f f e c t s , i n d i v -i d u a l l a m e l l a e h a v i n g s p e c i f i c • o p e n i n g p r e s s u r e s . M u i r (1970) h a s d i s c o v e r e d v a l v e - l i k e f l a p s o n b r a n c h e s o f a f f e r e n t fila™ m e n t a l a r t e r i e s i n t h e t u n a w h i c h may o c c l u d e o r d i r e c t f l o w t o w h o l e g r o u p s o f r e s p i r a t o r y l a m e l l a e ; s u c h s t r u c t u r e s h a v e n o t b e e n o b s e r v e d i n o t h e r t e l e o s t s . W h a t e v e r t h e o p e r a n t m e c h a n i s m s , t h e f a c t r e m a i n s t h a t d y n a m i c r e g u l a t i o n o f b l o o d d i s t r i b u t i o n b e t w e e n t h e h i g h v o l u m e r e s p i r a t o r y l a m e l l a e a n d lo w v o l u m e f i l a m e n t a l c h a n n e l s p r o v i d e s a p o s s i b l e e x p l a n a t i o n f o r " t h e m e a s u r e d r e s i s t a n c e c h a n g e s a c r o s s t h e b r a n c h i a l n e t v / o r k . H i s t o l o g i c a l a n d c y t o l o g i c a l i n v e s t i g a t i o n s o f g i l l t i s s u e h a v e d e t e r m i n e d g r o s s d i f f e r e n c e s b e t w e e n t h e s t r u c t u r e o f t h e l a m e l l a e and t h a t o f t h e f i l a m e n t s . The t y p i c a l r e s p -i r a t o r y l a m e l l a i s a d e l i c a t e f l a t t e n e d s t r u c t u r e , a b o u t 10 u t h i c k , s u p p o r t e d b y t h e a f o r e m e n t i o n e d p i l l a r c e l l s ; t h e s e c e l l b o d i e s e n c l o s e t h e v a s c u l a r a r e a . The b l o o d / w a t e r b a r r i e r , w i t h w h i c h an e r y t h r o c y t e makes i n t i m a t e c o n t a c t , c o m p r i s e s a n a r r o w e p i t h e l i u m , a b a s a l l a m i n a , a n d t h e c y t o p l a s m i c f l a n g e s 8 o f t h e p i l l a r c e l l s ; t o t a l w i d t h o f t h e b o u n d a r y i s 1 - 5 u (Hughes a n d G r i m s t o n e , 1 9 6 5 ; N e w s t e a d , 1 9 6 7 ) . The b l o o d s p a c e a c c o u n t s f o r a b o u t 70% o f t h e t o t a l l a m e l l a r v o l u m e (Hughes and G r i m s t o n e , 1 9 6 5 ) . A b r a n c h i a l f i l a m e n t , however, i s a l o n g , more c y l i n d r i c a l p r o c e s s c o v e r e d b y an i n t e r l a m e l l a e f i l a m e n t a l e p i t h e l i u m ( " s a l t s e c r e t o r y e p i t h e l i u m " ) o f 2 - 8 c e l l l a y e r s ( C o n t e , 1 9 6 9 ) . B e n e a t h t h i s l a y e r i s t h e c e n t r a l s i n u s , l i n e d w i t h e n d o t h e l i a l c e l l s a n d f i l l e d w i t h a n e t w o r k o f a n a s t o m o -s i n g c o n n e c t i v e t i s s u e ( S t e e n a n d K r u y s s e , 1 9 6 4 ) . T h e t h i c k -n e s s o f t h i s b l o o d / w a t e r b a r r i e r i s 10 - 30 t i m e s g r e a t e r t h a n t h e d i s t a n c e b e t w e e n t h e l a c u n a e o f t h e r e s p i r a t o r y l a m e l l a e a n d t h e e x t e r n a l medium. R e t u r n i n g now t o t h e d i f f u s i o n e q u a t i o n p r e s e n t e d on p a g e 4, i t c a n . b e s e e n how v a r i a t i o n s i n b r a n c h i a l b l o o d d i s t r i b u t i o n t h r o u g h v a s c u l a r s h u n t i n g w i l l c h a n g e some comp-o n e n t s o f t h e r e l a t i o n s h i p , t h e r e b y m o d i f y i n g e f f e c t i v e g i l l p e r m e a b i l i t y t o g a s e s , i o n s , a n d w a t e r . The mean d i f f u s i o n d i s t a n c e , X, w i l l o b v i o u s l y b e g r e a t l y r e d u c e d b y i n c r e a s e s i n l a m e l l a r b l o o d f l o w b e c a u s e o f t h e a b o v e d i f f e r e n c e s i n w i d t h o f t h e b l o o d / w a t e r b a r r i e r . T h e r e e x i s t no r e p o r t s r e l a t i n g t h e t o t a l a r e a s o f f i l a m e n t a l a n d l a m e l l a r s u r f a c e s ; h o w e v e r i t h a s b e e n p o s s i b l e , a s s u m i n g a mean f i l a m e n t d e p t h \ t h e a v e r a g e l e n g t h o f t h e l a m e l l a e ( f r o m t h e m i c r o g r a p h s o f Hughes a n d G r i m s t o n e , ( 1 9 6 5 ) ) t o c a l c u l a t e t h e s e v a l u e s f r o m t h e d a t a g i v e n b y Hughes ( 1 9 6 6 ) . F o r a 175 g s p e c i m e n o f Salmo  t r u t t a ( H u g h e s , 1 9 6 6 , p.180), t h e e n t i r e l a m e l l a r a r e a i s 2 a p p r o x i m a t e l y 6 t i m e s t h e t o t a l f i l a m e n t a l s u r f a c e (59,222 mm 2 v s . 10,5 75 mm ) . The a r e a p a r a m e t e r A o f t h e e q u a t i o n i s t h e r e f o r e e x t r e m e l y l a b i l e t o r e l a t i v e b l o o d f l o w s t h r o u g h t h e 9 two r e g i o n s . M a k i n g f u r t h e r s u p p o s i t i o n s o f a l a m e l l a r t h i c k n e s s e q u a l t o t h e d i a m e t e r o f an e r y t h r o c y t e a n d an a c c e s s i b l e b l o o d s p a c e o f 70% t o t a l v o l u m e i n b o t h t h e l a m e l l a e a n d t h e f i l a m e n t s , : t h e n t h e m a x i m a l v a s c u l a r v o l u m e o f t h e f o r m e r i s 1.7 x t h a t o f t h e f i l a m e n t b o d i e s (290 mnr v s . 3 173 mm ) . More i m p o r t a n t l y , t h e s u r f a c e a r e a t o b l o o d v o l u m e r a t i o o f t h e l a m e l l a r s h u n t s i s 3.3 t i m e s g r e a t e r t h a n t h a t o f t h e f i l a m e n t a l r o u t e s (203 mm - 1 v s . 61 mm - 1). T h i s d i f f e r e n c e i s e s p e c i a l l y i m p o r t a n t f o r g a s e x c h a n g e w h i c h i s s i g n i f i c a n t l y r e s t r i c t e d b y t h e d i f f u s i o n d i s t a n c e i n p l a s m a a n d c y t o p l a s m as w e l l as b y t h a t t h r o u g h t h e c e l l membrane ( K r o g h , 1 9 4 1 ; S t e e n a n d K r u y s s e , 1 9 6 4 ) . C o n c l u s i o n s as t o t h e e f f e c t s o f d i f f e r e n t i a l b l o o d f l o w t h r o u g h t h e v a r i o u s r o u t e s on D., t h e d i f f u s i o n o r o s m o t i c c o e f f i c i e n t , c a n o n l y be h y p o t h e t i c a l as no m e a s u r e m e n t s o f t h i s p a r a m e t e r f o r t h e s u b s t a n c e s o f i n t e r e s t h a v e b e e n made i n t e l e o s t t i s s u e . However i t seems l i k e l y t h a t t h e s i m p l e e p i t h e l i u m o f t h e l a m e l l a r w a l l p r o v i d e s l e s s d i f f u s i o n a l r e s i s t a n c e t h a n t h e d e n s e l y r e t i c u l a t e d and m i t o c h o n d r i a p a c k e d c e l l s o f t h e i n t e r l a m e l l a e f i l a m e n t a l e p i t h e l i u m . The i m p e r m e a b i l i t y o f t h e p l a s m a membrane t o l i p i d i n s o l u b l e i o n s a n d t o a l e s s e r e x t e n t w a t e r , i s s o s e v e r e t h a t t h e movement r a t e o f t h e s e s u b s t a n c e s i s d e t e r m i n e d s o l e l y b y t h e membrane ( D a v s o n , 1 9 6 4 ; Woodbury,1965 ) . However d i f f u s i o n c o -e f f i c i e n t s f o r t h e r e s p i r a t o r y g a s e s a r e r e l a t i v e l y s i m i l a r i n w a t e r an d t i s s u e ( K r o g h , 1 9 4 1 ) as t h e i r h i g h p a r t i t i o n c o -e f f i c i e n t s p e r m i t m i g r a t i o n d i r e c t l y t h r o u g h t h e p h o s p h o l i p i d p l a s m a membrane, r a t h e r t h a n t h r o u g h t h e r e s t r i c t i v e l e a k s , c e l l j u n c t i o n s , p o r e s , o r v e s i c l e s w h i c h a r e u s u a l l y p o s t u l a t e d 10 f o r e l e c t r o l y t e a n d w a t e r movement ( P a p p e n h e i m e r , 1 9 5 3; Woodbury 1965). A l l t h e s e c o n s i d e r a t i o n s i n d i c a t e t h a t t h e l a m e l l a r b l o o d p a t h w a y w i l l b e most e f f e c t i v e i n p r o m o t i n g g a s e x c h a n g e and l e a s t e f f e c t i v e i n p r e v e n t i n g o s m o t i c e x c h a n g e ; c o n v e r s e l y , t h e c e n t r a l f f i l a m e n t a l s h u n t s w i l l b e v i r t u a l l y n o n - f u n c t i o n a l i n r e s p i r a t i o n b u t h i g h l y e f f i c i e n t i n p r e v e n t i n g p a s s i v e f l u x e s o f s a l t s a n d w a t e r b e t w e e n p l a s m a an d e x t e r n a l medium. E v i d e n c e t h a t t e l e o s t s c a n , i n v i v o , d y n a m i c a l l y a d j u s t t h e b l o o d p e r f u s i o n o f d i f f e r e n t b r a n c h i a l p a t h w a y s as i n i s o l a t e d p r e p a r a t i o n s i s p r o v i d e d b y t h e l a r g e i n c r e a s e s i n o x y g e n c o n -s u m p t i o n o b s e r v e d d u r i n g e x e r c i s e i n s a l m o n i d s w i t h o u t s i g n i f i -c a n t v a r i a t i o n s i n t h e p a r t i a l p r e s s u r e g r a d i e n t f o r d i f f u s i o n ( S t e v e n s a n d R a n d a l l , 1 9 6 7 b ) . T h e a c c o m p a n y i n g r i s e i n t h e o x y g e n t r a n s f e r f a c t o r ( R a n d a l l e t a l . , 1 9 6 7 ) r e f l e c t s t h i s e f f e c t a n d i n d i c a t e s t h a t t h e g i l l p e r m e a b i l i t y must i n c r e a s e t h r o u g h d i v e r s i o n o f more b l o o d t o t h e r e s p i r a t o r y l a m e l l a e . I n c r e a s e d l a m e l l a r f l o v ; c a n be r e l a t e d t o t h e s i g n i f i c a n t e l e v a t i o n o f c i r c u l a t o r y c a t e c h o l a m i n e s d u r i n g a c t i v i t y ( Nakano an d T o m l i n s o n , 1 9 6 7 ) . The e e l , u n l i k e t h e t r o u t , d o e s n o t a l w a y s f u l l y s a t u r a t e b l o o d l e a v i n g t h e g i l l s ; S t e e n a n d K r u y s s e (1964) f o u n d t h a t d o r s a l a o r t i c FO^'s c o u l d be s i g n i -f i c a n t l y i n c r e a s e d b y i n t r a v a s c u l a r a d r e n a l i n e i n f u s i o n s . C a l c u l a t i o n s o f m e t a b o l i c r a t e b a s e d on e s t i m a t e d d i f f u s i o n c o e f f i c i e n t s and known g r a d i e n t s a n d d i s t a n c e s , and t h e anatom-i c a l a r e a o f t h e s e c o n d a r y l a m e l l a e , y i e l d v a l u e s g r e a t l y e x c e e d i n g r e s t i n g r a t e s ( S a u n d e r s , 1 9 6 2 ; S t e e n a n d K r u y s s e , 1 9 6 4 ; H u g h e s , 1 9 6 6 ) . C o n v e r s e l y , R a n d a l l ( 1 9 7 0 a ) h a s c o m p u t e d t h e f u n c t i o n a l l a m e l l a r a r e a f o r g a s e x c h a n g e i n t r o u t f r o m known 11 r e s t i n g s t a t e o x y g e n c o n s u m p t i o n ; t h e a r e a i m p l i c a t e d a t r e s t i s o n l y 20% o f t h e e n t i r e a n a t o m i c a l l a m e l l a r s u r f a c e r e p o r t e d b y H u ghes ( 1 9 6 6 ) . T h u s q u i e s c e n t f i s h must p e r f u s e o n l y a s m a l l number o f t h e i r r e s p i r a t o r y l a m e l l a e w i t h b l o o d , o r e l s e o n l y a s m a l l p o r t i o n o f e a c h l a m e l l a . T h e r e i s as y e t , h o w e v e r , v e r y l i t t l e e v i d e n c e f o r t h e o s m o t i c d e f i c i t w h i c h , b y t h e a b o v e a r g u m e n t s , s h o u l d be c o n c o m i t a n t w i t h i n c r e a s e d g a s e x c h a n g e . F a r m e r an d B e a m i s h (1969) f o u n d n o n - s i g n i f i c a n t d i f f e r e n c e s i n t h e o s m o l a r i t y o f p l a s m a b e t w e e n e x e r c i s e d a n d r e s t i n g T i l a p i a n i l o t i c a ; i n s e a w a t e r , p l a s m a c o n c e n t r a t i o n s e x c e e d e d t h o s e o f u n e x e r c i s e d f i s h ; t h e t r e n d was r e v e r s e d i n f r e s h w a t e r . S t e v e n s (1968 a) p o s t u l a t e d t h a t o b s e r v e d c h a n g e s i n h a e m o g l o b i n and p l a s m a p r o t e i n c o n c e n t r a t i o n s o f r a i n b o w t r o u t b l o o d d u r i n g s e v e r e a c t i v i t y w e r e a s s o c i a t e d w i t h i n c r e a s e d w a t e r f l u x e s . A c t i v i t y a n d c a t e c h o l a m i n e a d m i n i s t r a t i o n i n c r e a s e d t h e r e l e a s e o f i n -j e c t e d r a d i o s o d i u m f r o m t h e g i l l s o f t r o u t i n f r e s h w a t e r ( R a n d a l l e t a l . . 1969) . However, t h e s e e x p e r i m e n t s d i d n o t r e v e a l w h e t h e r any n e t e f f l u x o f s o d i u m o c c u r r e d . T h i s l a t t e r s t u d y p o i n t s up a c o m p l e x i t y i n c o n s i d e r i n g t h e i o n e x c h a n g e / g a s e x c h a n g e c o m p r o m i s e a t t h e b r a n c h i a l s u r f a c e w h i c h p r e v i o u s w o r k e r s h a v e n o t c o n s i d e r e d . H i s t o l o g i c a l a n d c y t o l o g i c a l e v i d e n c e now a s s i g n s a c t i v e e l e c t r o l y t e t r a n s p o r t f u n c t i o n o n l y t o t h e i n t e r l a m e l l a e f i l a m e n t a l e p i t h e l i u m w h i c h o v e r l i e s t h e c e n t r a l s i n u s b l o o d p a t h w a y ( s e e C o n t e , 1 9 6 9 ) an d n o t t o t h e w a l l s o f t h e r e s p i r a t o r y l a m e l l a e . R a d i o t r a c e r t e c h n i q u e s d e v e l o p e d by M a e t z a n d h i s c o - w o r k e r s ( e . g . M a e t z , 1 9 5 6 ; M o t a i s e t a l . , 1 9 6 6 ; M o t a i s , 1 9 6 7 ; M a e t z , 1 9 6 9 ) h a v e r e v e a l e d t h a t b o t h a c t i v e t r a n s p o r t a n d e x c h a n g e d i f f u s i o n o f i o n s o c c u r i n t h e 12 g i l l s . O b s e r v e d n e t f l u x e s may r e p r e s e n t o n l y a s m a l l p r o p -o r t i o n o f t h e t o t a l s a l t e x c h a n g e , w h i l e m e a s u r e m e n t s o f u n i -d i r e c t i o n a l f l u x e s a l o n e c a n n o t d e t e c t an i o n i c d e f i c i t . I t seems r e a s o n a b l e t h a t b r a n c h i a l b l o o d s h u n t i n g c o u l d a f f e c t c a r r i e r m e d i a t e d i o n i c t r a n s p o r t p r o c e s s e s as w e l l as e x e r t i n g s i m p l e p e r m e a b i l i t y e f f e c t s . I n c r e a s e d b l o o d f l o w t h r o u g h t h e c e n t r a l f i l a m e n t c o u l d unmask o r a c t i v a t e more t r a n s p o r t s i t e s , w h i l e g r e a t e r p e r f u s i o n o f t h e r e s p i r a t o r y p a t h w a y c o u l d d e c r e a s e t h e number o f c a r r i e r s i t e s i n o p e r a t i o n . Wood and R a n d a l l (1971) h a v e r e c e n t l y p r o v i d e d some s u p p o r t f o r t h i s h y p o t h e s i s . T h e p u r p o s e o f t h e p r e s e n t s t u d y was t o e x a m i n e t h a t c o m p o n e n t o f t h e r e s p i r a t o r y / o s m o r e g u l a t o r y c o m p r o m i s e i n t h e t e l e o s t g i l l w h i c h h a s p r e v i o u s l y r e c e i v e d c o n s i d e r a b l e s p e c u -l a t i o n b u t l i t t l e e x p e r i m e n t a l a t t e n t i o n , i o n and w a t e r e x c h a n g e . An i n t e n s i v e programme o f r e s e a r c h on t h e f r e s h w a t e r a d a p t e d r a i n b o w t r o u t , Salmo g a i r d n e r i , i n t h i s l a b o r a t o r y o v e r t h e p a s t s i x y e a r s h a s p r o d u c e d an u n d e r s t a n d i n g o f r e s p i r a t o r y and c a r d i o v a s c u l a r f u n c t i o n i n t h e s p e c i e s a n d a w e a l t h o f e x p e r i -m e n t a l t e c h n i q u e s . T h e s e f a c t o r s , c o m b i n e d w i t h t h e f i s h ' s a v a i l a b i l i t y i n u n i f o r m s i z e a n d c o n d i t i o n ; made i t an e x c e l l e n t e x p e r i m e n t a l a n i m a l on v/hich t h e m a j o r i t y o f t h e s t u d y was p e r f o r m e d . The same p r o b l e m , w i t h a s l i g h t l y d i f f e r e n t e m p h a s i s , was e x a m i n e d i n t h e s e a w a t e r a d a p t e d e u r y h a l i n e s o u t h e r n f l o u n d e r , P a r a l i c h t h y s l e t h o s t i g m a } i n somewhat l e s s e r d e t a i l ; t h e s e r e s u l t s h a v e b e e n r e p o r t e d e l s e w h e r e (Wood a n d R a n d a l l , 1 9 7 1 ) . The g e n e r a l i n v e s t i g a t i o n a l a p p r o a c h u t i l i z e d i n t h e p r e s e n t s t u d y was t o t r e a t g a s e x c h a n g e as t h e i n d e p e n d e n t 13 v a r i a b l e a n d e l e c t r o l y t e a n d w a t e r b a l a n c e as t h e d e p e n d e n t v a r i a b l e . T h u s c o n d i t i o n s known t o m o d i f y o x y g e n u p t a k e , a n d t h e r e f o r e g i l l b l o o d d i s t r i b u t i o n , were i m p o s e d on t h e a n i m a l a n d t h e a s s o c i a t e d s o d i u m a n d w a t e r f l u x e s q u a n t i f i e d . E x e r c i s e was u t i l i z e d a s a t o o l t o c h a n g e t h e g a s e x c h a n g e f a c t o r i n b r a n c h i a l " s i z e " ; e x t e n s i v e d a t a on t h e c a r d i o -v a s c u l a r a n d r e s p i r a t o r y e f f e c t s o f swimming i n s a l m o n i d s ( B r e t t , 1 9 6 4 ; S t e v e n s and R a n d a l l , 1 9 6 7 a, b; R a n d a l l e t a l . , 1967; S m i t h e t a l . , 1 9 6 7 ; S t e v e n s , 1 9 6 8 b; D a v i s , 1 9 6 8 ) w e r e a v a i l a b l e f o r c o m p a r i s o n . V a r i a t i o n s i n a c t i v i t y a r e p r o b a b l y t h e p r i m a r y c a u s e f o r r e d i s t r i b u t i o n o f b l o o d f l o w i n t h e g i l l s u n d e r n a t u r a l c i r c u m s t a n c e s . The o v e r a l l a i m o f t h e s t u d y was t o e v a l u a t e t h e e f f e c t s o f c h a n g i n g t h e r e s p i r a t o r y / o s m o r e g u l a t o r y b r a n c h i a l a d j u s t m e n t on s o d i u m and w a t e r r e g u l a t i o n i n r a i n b o w t r o u t , and t o d e t e r m i n e w h e t h e r compen-s a t o r y m e c h a n i s m s a r e i n v o k e d t o a l t e r t h e d y n a m i c s o f t h i s c o m p r o m i s e . 14 SECTION I THE E F F E C T OF EXERCISE (ONE HOUR) ON SODIUM BALANCE INTRODUCTION I The p r e s e n t l a c k o f i n f o r m a t i o n on t h e o s m o r e g u l a t o r y component o f t h e p o s t u l a t e d r e s p i r a t o r y / h y d r o e l e c t r o l y t e c o m p r o m i s e i n t h e t e l e o s t g i l l d u r i n g e x e r c i s e i s l a r g e l y a t t r i b u t a b l e t o t h e e x p e r i m e n t a l d i f f i c u l t i e s i n h e r e n t i n a t t a c k i n g t h e s u b j e c t . A v a r i e t y o f s a t i s f a c t o r y t e c h n i q u e s h a v e l o n g b e e n a v a i l a b l e f o r t h e i n v e s t i g a t i o n o f g a s e x c h a n g e d u r i n g a c t i v i t y i n f i s h ( s e e F r y , 1 9 5 7 ; B r e t t , 1 9 6 4 ; K l o n t z a n d S m i t h , 1 9 6 8 ) . However a l l s u c h swimming p r o c e d u r e s h a v e i n -v o l v e d t h e r e c i r c u l a t i o n o f r e l a t i v e l y l a r g e v o l u m e s o f w a t e r i n r e l a t i o n t o t h e s i z e o f t h e e x p e r i m e n t a l a n i m a l ; u n d e r s u c h c o n d i t i o n s , t h e u p t a k e o r r e l e a s e o f an e l e c t r o l y t e b y t h e f i s h f r o m o r t o t h e e x t e r n a l medium i s undetectable due t o m a s s i v e d i l u t i o n b o t h b y w a t e r a n d b y t h e mass o f i o n s o f t h e same s p e c i e s i n t h e medium. The o n l y p o s s i b i l i t y f o r d e t e c t i n g c h a n g e s i n o s m o r e g u l a t o r y f u n c t i o n s a s s o c i a t e d w i t h swimming u n d e r t h e s e c i r c u m s t a n c e s l i e s i n s a m p l i n g o f t h e a n i m a l ' s i n t e r n a l e n v i r o n m e n t . T h i s a p p r o a c h h a s b e e n t a k e n b y Rao ( 1968) and F a r m e r and B e a m i s h (1969)^ b u t has- p r o v e n r e l a t i v e l y u n i n f o r m a t i v e b e c a u s e o f t h e l a r g e n a t u r a l v a r i a b i l i t y i n c o n c e n t r a t i o n o f t e l e o s t p l a s m a c o n s t i t u t e n t s (Wedemeyer and C h a t t e r t o n , 1 9 7 0 ) a n d t h e i r l a b i l i t y t o t h e s t r e s s i n v o l v e d i n 1 5 s a m p l i n g p r o c e d u r e s ( H o u s t o n , p e r s o n a l c o m m u n i c a t i o n ) . E v e n when s u c h m e t h o d s h a v e b e e n a b l e t o d e t e c t s i g n i f i c a n t d i f f e r -e n c e s ( e . g . T o e w s , 1 9 6 9 ) , t h e r e s u l t s c a n s h e d l i t t l e l i g h t on t h e m e c h a n i s m s i n v o l v e d ; i t i s t h e o r e t i c a l l y p o s s i b l e f o r an a n i m a l t o g r e a t l y e l e v a t e o r d e p r e s s i t s s a l t t u r n o v e r r a t e w i t h o u t v a r i a t i o n i n s t e a d y s t a t e i n t e r n a l c o n c e n t r a t i o n s . W o r t h w h i l e i n v e s t i g a t i o n o f i o n i c b a l a n c e d u r i n g e x e r c i s e t h e r e f o r e demanded t h e u s e o f t e c h n i q u e s c a p a b l e o f d e t e c t i n g and q u a n t i f y i n g t h e d y n a m i c p r o c e s s e s i n v o l v e d . R a d i o t r a c e r m e t h o d s h a v e b e e n d e v e l o p e d f o r t h i s p u r p o s e ( M a e t z , 1 9 5 6 ; M a e t z an d G a r c i a - R o m e u , 1 9 6 4 ) w h i c h r e v e a l t h e i n f l u x , e f f l u x , a n d n e t f l u x c o m p o n e n t s o f e l e c t r o l y t e t r a n s f e r b e t w e e n t h e f i s h and i t s e x t e r n a l e n v i r o n m e n t . However, t h e s e m e t h o d s n e c e s s i t a t e t h e u s e o f w a t e r v o l u m e s o n l y a few t i m e s g r e a t e r t h a n t h a t o f t h e f i s h t o a c c u r a t e l y q u a n t i f y f l u x e s . A t t h e i n c e p t i o n o f t h e p r e s e n t s t u d y , a t t e m p t s were made t o e x e r c i s e f i s h i n v e r y s m a l l v o l u m e swimming r e s p i r o m e t e r s b u t f a i l e d due t o p r o b l e m s i n o b t a i n i n g l a m i n a r f l o w and t e m p e r -a t u r e r e g u l a t i o n i n t h e a p p a r a t u s . C o n s e q u e n t l y i t became n e c e s s a r y t o m o d i f y o r i g i n a l p l a n s f o r s i m u l t a n e o u s d e t e r m i n -a t i o n o f b o t h o x y g e n u p t a k e and b r a n c h i a l s o d i u m e x c h a n g e i n f a v o u r o f t h e more i m p o r t a n t o b j e c t i v e o f d i r e c t l y m e a s u r i n g o n l y t h e l a t t e r d u r i n g swimming i n t r o u t . E x e r c i s e was i m p o s e d on t h e f i s h t h r o u g h m a n u a l c h a s i n g i n a s m a l l a q u a r i u m ^ a n d f l u x r a t e s a s c e r t a i n e d d u r i n g a c t i v i t y c o m p a r e d w i t h v a l u e s d e t e r m i n e d on r e s t i n g a n d p o s t - e x e r c i s e a n i m a l s . C o l l e c t i o n o f u r i n e o u t s i d e t h e t a n k p r e v e n t e d r e n a l c o n t r i b u t i o n t o m e a s u r e d i o n i c e x c h a n g e . The q u a n t i t y o f e x t e r n a l w a t e r u s e d was a p p r o x i m a t e l y 3 t i m e s g r e a t e r t h a n t h a t d e s i r a b l e f o r 16 o p t i m a l p r e c i s i o n i n f l u x r a t e m e a s u r e m e n t s , b u t was t h e m i n i -mum v o l u m e w h i c h w o u l d s u p p o r t swimming a c t i v i t y i n c h a s e d f i s h y e t s t i l l y i e l d r e a s o n a b l y a c c u r a t e r a d i o t r a c e r d e t e r m i n -a t i o n s . The u s e o f s u c h a s y s t e m d i d n o t p e r m i t d i r e c t e v a l u -a t i o n o f t h e e x e r c i s e l e v e l i m p o s e d t h r o u g h m e a s u r e m e n t o f swimming s p e e d o r m e t a b o l i c r a t e . However p r o c e d u r e s f o r c a n n u l a t i o n o f t h e d o r s a l a o r t a ( S m i t h a n d B e l l , 1 9 6 4 ) and b r a n c h i a l c h a m b e r s ( S a u n d e r s , 1 9 6 2 ) h a v e r e c e n t l y b e e n a d o p t e d . t o m e a s u r e c a r d i o - r e s p i r a t o r y c h a n g e s i n s a l m o n i d s s u b j e c t e d t o swimming r e s p i r o m e t r y ( S t e v e n s and R a n d a l l , 1 9 6 7 a, fo; S m i t h e t a l . ,1967; D a v i s , 1968).. A p p l i c a t i o n o f t h e s e t e c h -n i q u e s t o t r o u t i n t h e p r e s e n t s t u d y p e r m i t t e d an e v a l u a t i o n o f t h e p h y s i o l o g i c a l s i g n i f i c a n c e o f t h e c h a s i n g p r o c e d u r e t h r o u g h c o m p a r i s o n w i t h t h e c a r d i o - r e s p i r a t o r y c h a n g e s ob -s e r v e d u n d e r more c o n t r o l l e d swimming c o n d i t i o n s b y o t h e r w o r k e r s . A f u r t h e r a d v a n t a g e o f v a s c u l a r c a t h e t e r i z a t i o n was t h e p r o v i s i o n o f a means f o r s e r i a l b l o o d s a m p l i n g w i t h o u t d i s t u r b a n c e t o t h e a n i m a l ; a s s a y o f p l a s m a a l i q u o t s f r o m t h e s e s a m p l e s p e r m i t t e d d e t e r m i n a t i o n o f i n t e r n a l s o d i u m l e v e l s a n d d i s t r i b u t i o n t h r o u g h o u t t h e e x p e r i m e n t . R a d i o t r a c e r t e c h n i q u e s o f t h i s t y p e h a v e n o t p r e v i o u s -l y b e e n a p p l i e d t o i n t a c t r a i n b o w t r o u t , Salmo g a i r d n e r i , and l i t t l e h a s b e e n r e p o r t e d a b o u t t h e p r o c e s s e s o f s o d i u m r e g u l -a t i o n i n t h e f r e s h w a t e r a d a p t e d f o r m o f t h i s s p e c i e s . I n o r d e r t o i n t e r p r e t p o s s i b l e c h a n g e s i n s o d i u m b a l a n c e a s s o c i a t e d w i t h r e a d j u s t m e n t o f t h e r e s p i r a t o r y / o s m o r e g u l a t o r y c o m p r o m i s e i n t h e g i l l , i t was n e c e s s a r y t o l e a r n as much as p o s s i b l e a b o u t b o t h t h e s t e a d y s t a t e and d y n a m i c d i s t r i b u t i o n o f t h e i o n w i t h i n t h e o r g a n i s m . T h u s a number o f f a c t o r s r e l a t e d t o t h i s t o p i c were m e a s u r e d i n a d d i t i o n t o b r a n c h i a l f l u x r a t e s . T he o b j e c t o f t h i s s e c t i o n was t h e r e f o r e t w o f o l d : ( i ) t o d e s c r i b e s o d i u m " m e t a b o l i s m " i n t h e f r e s h w a t e r a d a p t e d r a i n b o w t r o u t ( i i ) t o e x a m i n e t h e e f f e c t o f e x e r c i s e and r e c o v e r y f r o m e x e r c i s e on t h e p r o c e s s e s i n v o l v e d i n s o d i u m r e g u l a t i o n i n t h i s t e l e o s t . 18 METHODS I 1. E x p e r i m e n t a l A n i m a l s A l l f i s h u s e d i n t h i s s t u d y were s e x u a l l y m a t u r e r a i n -bow t r o u t ( S a l m o g a i r d n e r i ) o b t a i n e d f r o m a c o m m e r c i a l s u p p l i e r , Sun V a l l e y T r o u t Farm, P o r t C o q u i t l a m , B.C. The t r o u t w e i g h e d b e t w e e n 180 a n d 350 g . The a n i m a l s were h e l d a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a i n l a r g e o u t d o o r c o n c r e t e o r g a l v a n i z e d s t e e l t a n k s s u p p l i e d w i t h d e c h l o r i n a t e d f r e s h w a t e r a t s e a s o n a l t e m p e r a t u r e s . D u r i n g t h i s t i m e , t h e f i s h w ere f e d w e e k l y w i t h c o m m e r c i a l t r o u t p e l l e t s . E x p e r i m e n t s w e r e p e r f o r m e d d u r i n g t h e p e r i o d f r o m May t o December, 1969. P r i o r t o e x p e r i m e n t a t i o n , t h e t r o u t were t r a n s f e r r e d t o one o f two i n d o o r 160 g a l l o n c o n c r e t e t a n k s a n d h e l d a t 1 4 . 5 - 1 . 5 ° C . f o r 1 - 4 weeks. E a c h t a n k was s u p p l i e d w i t h a g l a s s c o o l i n g c o i l a n d two 250 w a t t a q u a r i u m h e a t e r s . D u r i n g November and December, l i g h t s s i t u a t e d i n t h e c o v e r s o f t h e t a n k s w e r e u t i l i z e d a s s u p p l e m e n t a l h e a t s o u r c e s t o m a i n t a i n t h e a c c l i m a t i o n t e m p e r a t u r e . The d e c h l o r i n a t e d f r e s h w a t e r i n e a c h t a n k was c o n t i n u a l l y a e r a t e d a n d r e c i r c u l a t e d t h r o u g h an a c t i v a t e d c h a r c o a l and F i b e r g l a s f i l t e r , a n d p a r t i a l l y r e p l a c e d a t w e e k l y i n t e r v a l s . P e r i o d i c d e t e r m i n a t i o n s o f s o d i u m c o n c e n t r a t i o n i n t h e a c c l i m a t i o n f a c i l i t y w a t e r y i e l d e d v a l u e s f r o m 1.0 - 4.0 u g / m l . A t t h e t i m e o f t r a n s f e r , most t r o u t w e r e l i g h t l y a n a e s t h e t i z e d w i t h MS 222 a n d l a b e l l e d w i t h c o l o u r e d c o t t o n t h r e a d s sewn i n t o t h e d o r s a l a n d c a u d a l f i n s t o s e p a r a t e 19 d i f f e r e n t a c c l i m a t i o n b a t c h e s . No more t h a n 20 f i s h w e r e h e l d i n e a c h t a n k a t any one t i m e . D u r i n g t h e a c c l i m a t i o n p e r i o d , t h e a n i m a l s were n o t f e d i n o r d e r t o a v o i d f a e c a l c o n t a m i n a t i o n o f t h e e x t e r n a l w a t e r i n s u b s e q u e n t e x p e r i m e n t s . 2. O p e r a t i n g P r o c e d u r e s and C a n n u l a t i o n s D o r s a l a o r t i c , b u c c a l , and u r i n a r y c a n n u l a e w e r e i m -p l a n t e d i n a l l e x p e r i m e n t a l f i s h . T r o u t were a n a e s t h e t i z e d i n w a t e r c o n t a i n i n g 1/15,000 MS 222 a n d t h e n p l a c e d v e n t r a l s i d e up on an o p e r a t i n g t a b l e ( S m i t h a n d B e l l , 1 9 6 4 ) . The t a b l e was s o c o n s t r u c t e d t h a t e i t h e r an a n a e s t h e t i c s o l u t i o n ( 1 / 2 0 , 0 0 0 MS 222) o r f r e s h w a t e r c o u l d b e p e r f u s e d t h r o u g h t h e mouth o r b a c k w a r d s o v e r t h e g i l l s . The d u r a t i o n o f t h e e n t i r e o p e r a t i o n was a b o u t 30 m i n u t e s . D u r i n g t h i s t i m e , w a t e r t e m p e r a t u r e was n o t c o n t r o l l e d , b u t r e m a i n e d i n t h e r a n g e o f 1 1 ° C . t o 1 7 ° C . The f o l l o w i n g c a n n u l a t i o n s w e r e p e r f o r m e d : ( a ) B u c c a l C a v i t y C a n n u l a t i o n ( F i g . l ) A s m a l l h o l e was p u n c h e d t h r o u g h t h e c a r t i l a g i n o u s p o r t i o n o f t h e s n o u t s l i g h t l y l e f t o f t h e m i d l i n e u s i n g an i r i s s c a l p e l . C a r e was t a k e n t o a v o i d damage t o e i t h e r t h e e x -t e r n a l n a r i s o r t h e b u c c a l v a l v e s i n b o t h t h i s a n d t h e d o r s a l a o r t i c c a n n u l a t i o n t e c h n i q u e . E i g h t y cm o f PE 60 p o l y e t h y l e n e t u b i n g ( C l a y - A d a m s ) , w i t h a h e a t f l a r e d t i p t o a c t as an a n c h o r , was p a s s e d o u t t h r o u g h t h i s h o l e and t i e d on t h e d o r s a l s i d e o f t h e r o s t r u m . (b) D o r s a l A o r t i c C a n n u l a t i o n ( F i g . l ) T he d o r s a l a o r t a was c a n n u l a t e d i n t h e m i d l i n e a t t h e l e v e l o f t h e f i r s t g i l l a r c h ( S m i t h a n d B e l l , 1 9 6 4 ) w i t h a #21 20 Figure 1 A drawing of the a n t e r i o r p o r t i o n of a rainbow trout showing the l o c a t i o n and s i z e of the buccal and dorsal a o r t i c cannulae used i n the experiments of Section I. PE 60 tubing dorsal aortic cannula buccal cannula PE 200 jacket tied around PE 60 tubing heat flared tips H u b e r p o i n t n e e d l e c o n n e c t e d t o 80 cm o f PE 60 t u b i n g . The c a t h e t e r was p a s s e d o u t o f t h e b u c c a l c a v i t y t h r o u g h a h o l e p u n c h e d o n t h e r i g h t h a n d s i d e o f t h e s n o u t ; t h e h o l e was l i n e d w i t h a s h o r t l e n g t h o f h e a t - f l a r e d PE 200 t u b i n g . The PE 60 was l o o s e l y a n c h o r e d t o t h e r o o f o f t h e mouth w i t h one o r two s i l k s t i t c h e s , a n d t h e PE 200 j a c k e t t i e d t i g h t l y a r o u n d t h e i n n e r t u b i n g a t i t s p o i n t o f e m e r g e n c e f r o m t h e s n o u t t o p r e v e n t i n w a r d movement o f t h e c a n n u l a . I m m e d i a t e l y a f t e r s u c c e s s f u l c a t h e t e r i z a t i o n , 0.5 ml o f h e p a r i n i z e d (20 I.U./ml) C o r t l a n d s a l i n e ( W o l f , 1 9 6 3 ) was i n f u s e d i n t o t h e d o r s a l a o r t a t o p r e v e n t c l o t t i n g / and t h e c a n n u l a p l u g g e d w i t h a s t a i n l e s s s t e e l p i n . B o t h c a t h e t e r s w e r e a n c h o r e d w i t h a s i n g l e s t i t c h t o t h e d o r s a l s i d e o f t h e f i s h a p p r o x i m a t e l y 6 cm p o s t e r i o r t o t h e s n o u t . ( c ) U r i n a r y C a n n u l a t i o n ( F i g . 2 ) A u r i n a r y c a n n u l a was c o n s t r u c t e d b y g l u i n g , w i t h e p o x y r e s i n , a p p r o x i m a t e l y 1.5 cm o f . PE 190 a r o u n d an 80 cm l e n g t h o f PE 60 a p p r o x i m a t e l y 1.5 cm f r o m t h e t i p o f t h e l a t t e r . T h i s e n d o f t h e s m a l l e r t u b i n g h a d b e e n v e r y l i g h t l y h e a t p o l i s h e d . The d i s t a l e n d o f t h e PE 190 j a c k e t h a d b e e n h e a v i l y h e a t f l a r e d , a n d t h e p r o x i m a l e n d s i m i l a r l y f l a t t e n e d , b u t t o a l e s s e r d e g r e e . Numerous s m a l l h o l e s were p u n c h e d i n t h e p r o x i m a l 0.5 cm o f PE 60 w i t h a h e a t e d #22 n e e d l e . S u c c e s s f u l c a n n u l a t i o n was f a c i l i t a t e d b y h a v i n g a v a r i e t y o f p r e - c o n s t r u c t e d c a t h e t e r s on h a n d , r e p r e s e n t i n g a r a n g e o f f l a r e w i d t h s , j a c k e t l e n g t h s , a n d p r o x i m a l t i p l e n g t h s . A c a n n u l a c o u l d t h e n be f i t t e d t o t h e p a r t i c u l a r u r o g e n i t a l mor-p h o l o g y o f a s p e c i f i c t r o u t ; l e n g t h a n d d i a m e t e r o f t h e u r o -22 Figure 2 Upper: A drawing of the construction of the proximal end of the urinary catheter. Lower: A drawing of the placement and f i x a t i o n of the urinary catheter used i n t h i s study. PE 60 tubing P E 1 9 0 i a c k e t h e a t polished tip [V. distal flange holes punched with proximal flange * 2 2 n e e d l e stitch in ventral body wall g e n i t a l p a p i l l a e a r e f e a t u r e s w h i c h v a r y w i d e l y among i n d i v i -d u a l f i s h . C a n n u l a t i o n was p e r f o r m e d b y o p e n i n g t h e a p e r t u r e o f t h e u r o g e n i t a l p a p i l l a w i t h a p a i r o f f i n e f o r c e p s , and i n s e r t -i n g t h e p r o x i m a l t i p o f t h e c a t h e t e r d o r s a d u n t i l t h e p r o x i m a l f l a n g e o f t h e PE 200 j a c k e t was j u s t i n s i d e t h e p a p i l l a . The p a p i l l a was t h e n t i e d t i g h t l y a r o u n d t h e j a c k e t b e h i n d t h e p r o x i m a l f l a n g e w i t h two s i l k l i g a t u r e s . D u r i n g t h e c a n n u l -a t i o n p r o c e d u r e , t h e c a t h e t e r was f i l l e d w i t h C o r t l a n d s a l i n e . I m m e d i a t e l y f o l l o w i n g i n s e r t i o n , 0.5 ml o f s a l i n e was i n f u s e d i n t o t h e u r i n a r y s y s t e m and t h e c a n n u l a p l u g g e d w i t h a p i n . A s t i t c h was t h e n t i e d i n t o t h e v e n t r a l b o d y w a l l b e t w e e n t h e p e l v i c f i n s a n d t h e l o o s e e n d s o f t h r e a d l e d b a c k a r o u n d t h e d i s t a l f l a n g e o f t h e c a t h e t e r i n a p u r s e s t r i n g l i g a t u r e . T e n s i o n o f t h e t h r e a d s was a d j u s t e d s u c h t h a t a v e n t r o - c a u d a d p u l l on t h e c a n n u l a e x e r t e d f o r c e o n t h e v e n t r a l b o d y w a l l r a t h e r t h a n on t h e d e l i c a t e p a p i l l a i t s e l f . F i n a l l y t h e c a t h e t e r was l o o s e l y a n c h o r e d t o t h e a n a l f i n w i t h a s i n g l e s i l k s t i t c h . The p l u g was r e m o v e d f r o m t h e c a n n u l a o n l y when t h e f i s h was r e t u r n e d t o w a t e r , a n d was r e i n s e r t e d d u r i n g any f u r t h e r t r a n s f e r p r o c e d u r e s . T h i s t e c h n i q u e o f u r i n a r y c a t h e t e r i z a t i o n e v o l v e d f r o m t r i a l s w i t h many d i f f e r e n t p r o c e d u r e s . From t h e p o i n t o f v i e w o f t h e demands p l a c e d on t h e c a n n u l a e b y t h e e x p e r i -m e n t a l p r o t o c o l i n t h i s s t u d y , t h e m e t h o d seemed s u p e r i o r t o o t h e r p u b l i s h e d t e c h n i q u e s ( e . g . E n o m o t o , 1 9 6 7 ; Holmes an d S t a i n e r , 1966; Hammond,1969) f o r s e v e r a l d i f f e r e n t r e a s o n s : ( i ) The p u r s e s t r i n g l i g a t u r e e n s u r e d d u r a b i l i t y o f t h e p r e p a r a t i o n d u r i n g t h e e x p e r i m e n t a l e x e r c i s i n g 24 p r o c e d u r e . ( i i ) T h e p r e s e n c e o f a l a r g e number o f h o l e s i n t h e c o l l e c t i n g t i p o f t h e c a t h e t e r r e d u c e d t h e i n c i d -e n c e o f mucous o c c l u s i o n . ( i i i ) L i g a t i o n o f t h e u r o g e n i t a l p a p i l l a b e h i n d a f l a n g e p r e v e n t e d l e a k a g e o f u r i n e a r o u n d t h e o u t s i d e o f t h e c a t h e t e r . F o l l o w i n g c o m p l e t i o n o f t h e a b o v e p r o c e d u r e s , t h e f i s h was r e -v i v e d b y p e r f u s i o n o f t h e g i l l s w i t h f r e s h w a t e r a n d t h e n t r a n s -f e r r e d t o a t e m p e r a t u r e c o n t r o l l e d (14.5^*1.5°C.) 15 g a l l o n a q u a r i u m f o r a r e c o v e r y p e r i o d o f 10 t o 48 h o u r s . 3. E x p e r i m e n t a l S y s t e m S u c c e s s f u l e x p e r i m e n t s w e r e p e r f o r m e d o n 32 r a i n b o w t r o u t p r e p a r e d as d e s c r i b e d a b o v e ; r e s u l t s f r o m a number o f o t h e r f i s h w ere r e j e c t e d b e c a u s e o f c a n n u l a e f a i l u r e a n d / o r c o n t a m i n a t i o n o f s a m p l e s . The t r o u t were d i v i d e d i n t o t h r e e t r e a t m e n t g r o u p s o f a p p r o x i m a t e l y e q u a l s i z e : r e s t i n g , a c t i v e , a n d r e c o v e r y . The e x p e r i m e n t s c o n s i s t e d o f s i m u l t a n e o u s m e a s u r e m e n t s o f s o d i u m i n f l u x , e f f l u x , a n d n e t f l u x r a t e s , p l a s m a s o d i u m l e v e l s , r a d i o s o d i u m s p a c e s , u r i n e p r o d u c t i o n r a t e s , d o r s a l a o r t i c b l o o d p r e s s u r e s , b u c c a l p r e s s u r e a m p l i -t u d e s , v e n t i l a t o r y a n d c a r d i a c r a t e s , a n d h e m a t o c r i t s i n e a c h t r e a t m e n t g r o u p o v e r a one o r two h o u r p e r i o d . I n a d d i t i o n , s a m p l e s f o r d e t e r m i n a t i o n o f p l a s m a a n d t i s s u e w a t e r , e x t r a -c e l l u l a r f l u i d v o l u m e , an d t i s s u e r a d i o s o d i u m a n d t o t a l s o d i u m l e v e l s w e r e t a k e n a t t h e e n d o f t h e e x p e r i m e n t f o r e a c h s e t o f a n i m a l s . (a) E x p e r i m e n t a l Chamber ( F i g . 3 ) A l l e x p e r i m e n t s w e r e p e r f o r m e d i n a s m a l l g l a s s a q u a -r i u m ( l e n g t h = 35 cm; w i d t h = 20 cm; d e p t h = 24 cm) c o n t a i n i n g 5.5 o r 6.0 L o f d e c h l o r i n a t e d f r e s h w a t e r (mean s o d i u m c o n c e n -t r a t i o n = 1.70 ug/ml) and c o v e r e d on a l l s i d e s w i t h b l a c k p l a s t i c t o r e d u c e v i s u a l s t i m u l a t i o n . The a q u a r i u m was e q u i p p e d w i t h a g l a s s s t a n d p i p e a n d f u n n e l f o r t h e a d d i t i o n o f 22 Na s o l u t i o n s o r a n a e s t h e t i c w i t h o u t d i s t u r b a n c e t o t h e f i s h , p o l y t h y l e n e t u b i n g f o r t h e w i t h d r a w a l o f s a m p l e s f r o m b e n e a t h t h e w a t e r l e v e l , a n d a i r s t o n e s t o p r o v i d e a d e q u a t e a e r a t i o n a n d m i x i n g o f t h e w a t e r . T h e chamber was s u s p e n d e d i n s i d e a w a t e r f i l l e d 15 g a l l o n a q u a r i u m c o n t a i n i n g a r e f r i g e r a t i o n u n i t w i t h t e m p e r a t u r e r e l a y . The a p p a r a t u s m a i n t a i n e d a s t a b l e t e m p e r a t u r e o f 1 4 . 5 i o . 5 ° C . i n t h e e x p e r i m e n t a l t a n k . A d -22 s o r p t i o n o f Na b y t h e g l a s s w a l l s o f t h e a q u a r i u m was n e g l i g i b l e . (b) T r e a t m e n t G r o u p s and E x p e r i m e n t a l P r o c e d u r e C a n n u l a t e d t r o u t were t r a n s f e r r e d t o t h e s m a l l a q u a r i u m c o n t a i n i n g 5.5 L o f w a t e r and l e f t u n d i s t u r b e d f o r a t l e a s t 2 h o u r s p r i o r t o t h e s t a r t o f an e x p e r i m e n t . D o r s a l a o r t i c a n d b u c c a l c a n n u l a e w e r e a t t a c h e d t o p r e s s u r e t r a n s -d u c e r s i m m e d i a t e l y a f t e r t h i s t r a n s f e r . The u r i n a r y c a t h e t e r , h o w e v e r , was l e d o u t o f t h e chamber o n l y a few m i n u t e s b e f o r e t h e b e g i n n i n g o f an e x p e r i m e n t t o a v o i d e x c e s s i v e t a n g l i n g o f t h e 3 p i e c e s o f t u b i n g . ( i ) R e s t i n g T r o u t . A t z e r o t i m e , 500 ml o f f r e s h 22 w a t e r c o n t a i n i n g a known amount o f Na C l (7 - l O u C . ) were 22 a d d e d t o t h e a q u a r i u m . T h e c h a n g e s i n t o t a l s o d i u m and Na c o n c e n t r a t i o n s o f t h e e x t e r n a l medium were m o n i t o r e d o v e r t h e Figure 3 A drawing of the experimental system used i n Section dorsal aortic cannula > blood //^sampl ing buccal cannula pressure transducers funnel and stand-pipe for addition of N a " solution or MS 222 constant temperature bath experimental chamber refrigeration coil with temperature relay airstone water level in experimental chamber f o l l o w i n g 60 m i n u t e s ; w a t e r r a d i o a c t i v i t y g e n e r a l l y d e c l i n e d b y 33 - 5 0 % o f t h e z e r o t i m e l e v e l . W i t h t h e e x c e p t i o n o f p e r i o d i c b l o o d s a m p l i n g f r o m t h e d o r s a l a o r t i c c a t h e t e r , t h e f i s h w e r e l e f t u n d i s t u r b e d d u r i n g t h i s t i m e . A t 60 m i n u t e s , a s o l u t i o n o f MS 222 s u f f i c i e n t t o p r o v i d e a c o n c e n t r a t i o n o f 1/10,000 i n t h e e x t e r n a l medium was a d d e d t o t h e c h a m b e r . I m m e d i a t e l y a f t e r l o s s o f e q u i l i b r i u m , t h e f i s h was r e m o v e d f r o m t h e a q u a r i u m a n d s t u n n e d b y a b l o w on t h e h e a d i n p r e p -a r a t i o n f o r i m m e d i a t e t i s s u e s a m p l i n g a n d w e i g h i n g p r o c e d u r e s . F i n a l l y , t h e p a t e n c y o f t h e u r i n a r y c a t h e t e r was c h e c k e d b y i n j e c t i o n o f a s m a l l amount o f d y e d s a l i n e i n t o t h e c a n n u l a , f o l l o w e d b y g e n t l e p r e s s u r e on t h e v e n t r o - p o s t e r i o r b o d y w a l l . A l l d a t a f r o m t r o u t e x h i b i t i n g l e a k a g e , a n d t h e r e f o r e t h e r e l e a s e o f u r i n e d u r i n g t h e e x p e r i m e n t , w e r e d i s c a r d e d . ( i i ) A c t i v e T r o u t . The f i s h was c h a s e d m a n u a l l y w i t h : a f i r e - p o l i s h e d g l a s s r o d d u r i n g t h e e x p e r i m e n t a l h o u r . C h a s i n g was t e r m i n a t e d 1 m i n u t e b e f o r e e a c h b l o o d s a m p l i n g and r e s u m e d 1 m i n u t e a f t e r i t s c o m p l e t i o n . As e a c h o f t h e 5 b l o o d s a m p l i n g p r o c e d u r e s d u r i n g t h e h o u r t o o k a p p r o x i m a t e l y 2 m i n -u t e s , t h e t r o u t was k e p t a c t i v e f o r a b o u t o n l y 40 m i n u t e s o u t o f a t o t a l o f 60. I n e f f e c t , m e r e l y an o c c a s i o n a l movement o f t h e r o d was s u f f i c i e n t t o k e e p t h e a n i m a l swimming d u r i n g t h e f i r s t m i n u t e s o f t h e e x p e r i m e n t . However b y t h e e n d o f t h e h o u r , i t became n e c e s s a r y t o c o n t i n u a l l y t a p t h e f i s h i n t h e c a u d a l r e g i o n t o i n d u c e a c t i v i t y . W i t h . p r a c t i c e , i t was p o s s i b l e t o a v o i d e x c e s s i v e t a n g l i n g o f t h e t h r e e c a n n u l a e t h r o u g h p e r i o d i c r e v e r s a l s o f t h e d i r e c t i o n o f c h a s i n g . I n o t h e r a s p e c t s , t h e e x p e r i m e n t a l p r o c e d u r e was i d e n t i c a l t o t h a t u s e d f o r t h e r e s t i n g t r o u t . 28 ( i i i ) R e c o v e r y T r o u t . As f o r t h e a c t i v e e x p e r i m e n t s , t h e f i s h was c h a s e d o v e r a one h o u r p e r i o d . However, no r a d i o -i s o t o p e was a d d e d t o t h e chamber a t z e r o t i m e ; t h u s t h e v o l u m e o f w a t e r i n t h e a q u a r i u m r e m a i n e d a t 5.5 L f o r t h e f i r s t 60 m i n u t e s . I n a d d i t i o n , no b l o o d s a m p l e s were w i t h d r a w n , b u t c h a s i n g was t e r m i n a t e d f o r 4 m i n u t e p e r i o d s a t t i m e s c o r r e s -p o n d i n g t o t h e i n t e r r u p t i o n s n e c e s s i t a t e d b y b l o o d s a m p l i n g i n t h e a c t i v e f i s h . A t 60 m i n u t e s , 500 ml o f w a t e r c o n t a i n i n g 22 7 - l O u C o f Na C l . were a d d e d t o t h e e x t e r n a l medium, an d t h e e x p e r i m e n t p r o c e e d e d f o r a n o t h e r h o u r w i t h m e t h o d s i d e n t i c a l t o t h o s e u s e d f o r r e s t i n g a n i m a l s . ( c ) R e c o r d i n g T e c h n i q u e s D o r s a l a o r t i c b l o o d p r e s s u r e s a n d b u c c a l p r e s s u r e s were m e a s u r e d t h r o u g h o u t t h e e x p e r i m e n t i n a l l t h r e e t r e a t m e n t g r o u p s i n an a t t e m p t t o q u a n t i f y t h e p h y s i o l o g i c a l s i g n i f i c a n c e o f t h e a c t i v i t y l e v e l i m p o s e d o n t h e f i s h b y c h a s i n g . H e a r t r a t e a n d b r e a t h i n g r a t e c o u l d a l s o be a s c e r t a i n e d f r o m t h e r e c o r d i n g s . E a c h c a n n u l a was c o n n e c t e d t o a S t a t h a m P-23 B.B. ( v e n o u s ) p r e s s u r e t r a n s d u c e r . The p r e s s u r e c h a n g e s were d i s -p l a y e d t o g e t h e r w i t h a t i m e s i g n a l o n two c h a n n e l s o f a Beckman T y p e R.S. D y n o g r a p h R e c o r d e r . The s y s t e m was e l e c t -r i c a l l y b a l a n c e d a t z e r o a g a i n s t t h e w a t e r l e v e l i n t h e t a n k b e f o r e e a c h e x p e r i m e n t and c a l i b r a t e d a t t h e e n d o f e a c h r u n . F l u c t u a t i o n s i n w a t e r l e v e l due t o movement o f t h e f i s h , w a t e r 22 s a m p l i n g , a n d a d d i t i o n o f t h e Na C l s o l u t i o n p r e v e n t e d comp-u t a t i o n o f e x a c t p o s i t i v e a n d n e g a t i v e p r e s s u r e s i n t h e b u c c a l c a v i t y ; h o w e v e r , t h e t o t a l p r e s s u r e a m p l i t u d e o f t h e r e s p i r -a t o r y movements was s t i l l o b t a i n a b l e f r o m t h e r e c o r d s . A f t e r t h e f i r s t few t r i a l s , i t became a p p a r e n t t h a t b o t h t r a c e s 29 became h i g h l y i r r e g u l a r d u r i n g c h a s i n g ( s e e F i g . 4 ) . T h u s s y s t e m a t i c p r e s s u r e r e c o r d i n g s were g e n e r a l l y o n l y t a k e n d u r i n g t h e 1 m i n u t e i n t e r v a l b e f o r e a n d a f t e r e a c h b l o o d s a m p l i n g p e r i o d ; r e c o r d i n g s f r o m a c t i v e t r o u t a r e , t h e r e f o r e , r e p r e s e n t -a t i v e o f an i m m e d i a t e l y p o s t - e x e r c i s e c o n d i t i o n , (d) S a m p l i n g P r o c e d u r e s A l l a p p a r a t u s u s e d i n t h e h a n d l i n g and s u b s e q u e n t p r o c e s s i n g o f w a t e r , p l a s m a , a n d t i s s u e s a m p l e s h a d b e e n c a r e -f u l l y w a s h e d w i t h g l a s s - d i s t i l l e d w a t e r a n d d r i e d p r i o r t o u s e . ( i ) ..Water S a m p l e s . T e n ml w a t e r s a m p l e s were drawn f r o m t h e a q u a r i u m t h r o u g h PE 60 t u b i n g i n t o p l a s t i c s y r i n g e s ; s a m p l e s w e r e s u b s e q u e n t l y t r a n s f e r r e d t o p o l y e t h y l e n e v i a l s ( N a l g e n e C o r p o r a t i o n ) and f r o z e n a t - 1 2 ° C . F o r a l l g r o u p s , z e r o t i m e r e p r e s e n t e d t h e s t a r t o f t h e e x p e r i m e n t b u t c o i n c i d e d w i t h t h e a d d i t i o n o f i s o t o p e t o t h e chamber i n o n l y t h e r e s t i n g a n d a c t i v e t r e a t m e n t s . S a m p l e s were w i t h d r a w n a t z e r o t i m e , 1, 5, 15, 30, 45, a n d 60 m i n u t e s d u r i n g t h e r e s t i n g a n d a c t i v e e x p e r i m e n t s , w h i l e i n t h e r e c o v e r y s t u d i e s , w a t e r was r e m o v e d a t z e r o t i m e , 5, 15, 30, 45, 58, 61, 65, 75, 90, 105, 22 a n d 120 m i n u t e s . I n a d d i t i o n , a l i q u o t s o f t h e Na s o l u t i o n w ere t a k e n i n a l l e x p e r i m e n t s . ( i i ) B l o o d S a m p l e s . B l o o d s a m p l e s were w i t h d r a w n v i a t h e d o r s a l a o r t i c c a t h e t e r f r o m r e s t i n g a n d a c t i v e t r o u t a t z e r o t i m e ( a p p r o x i m a t e l y 100 uL) a n d 5, 15, 30, 45, and 60 m i n u t e s ( a l l a p p r o x i m a t e l y 200 u L ) ; ( t o t a l v o l u m e r e m o v e d i n c l u d i n g " s p i l l a g e " = 1.45 m l ) . From r e c o v e r y f i s h , b l o o d was t a k e n a t z e r o t i m e a n d 60 m i n u t e s ( b o t h 100 uL) a n d a t 65, 75, 90, 105, and 120 m i n u t e s ( a l l 200 u L ) ; ( t o t a l v o l u m e r e m o v e d i n c l u d i n g " s p i l l a g e " = 1.60 m l ) . B l o o d was a l l o w e d 30 t o f l o w f r o m t h e c a t h e t e r i n t o a 1 ml p l a s t i c s y r i n g e u n d e r i t s own p r e s s u r e o r u n d e r s l i g h t s u c t i o n . T h e s y r i n g e h a d b e e n p r e -r i n s e d w i t h a 100 I.U./ml s o d i u m h e p a r i n / d i s t i l l e d w a t e r s o l -u t i o n a n d a l l o w e d t o d r y ; t h i s l e v e l o f h e p a r i n i z a t i o n was a d e q u a t e t o p r e v e n t c l o t t i n g o r h a e m o l y s i s b u t was n o t g r e a t e n o u g h t o c a u s e s i g n i f i c a n t s o d i u m c o n t a m i n a t i o n o f p l a s m a s a m p l e s . As i t was i m p o s s i b l e f o r a s i n g l e e x p e r i m e n t e r t o t a k e b l o o d a n d w a t e r s a m p l e s s i m u l t a n e o u s l y , t h e f o l l o w i n g scheme was u s e d . A s p i r a t i o n o f w a t e r commenced 15 s e c o n d s b e f o r e t h e d e s i g n a t e d t i m e a n d l a s t e d a p p r o x i m a t e l y 30 s e c o n d s ; o n l y t h e n was b l o o d s a m p l i n g ( a 1 t o 2 m i n u t e p r o c e d u r e ) s t a r t e d . T h u s w h i l e w a t e r s a m p l e s were on t i m e , b l o o d s a m p l e s were s y s t e m a t i c a l l y 90 s e c o n d s l a t e . _ _ The b l o o d s a m p l i n g t e c h n i q u e was d e s i g n e d as a c o m p r o m i s e t o r e d u c e t h r e e u n d e s i r a b l e e f f e c t s : 1. C o n t a m i n a t i o n o f t h e b l o o d a l i q u o t w i t h s a l i n e t h r o u g h " s m e a r i n g " i n t h e c a n n u l a . 2. R e d u c t i o n o f i n t e r n a l s o d i u m l e v e l s a n d h e m a t o c r i t t h r o u g h e x c e s s i v e b l e e d i n g . 3. C o n t a m i n a t i o n o f p l a s m a s t i l l i n s i d e t h e t r o u t t h r o u g h t h e r e i n t r o d u c t i o n o f b l o o d m i x e d w i t h s a l i n e . T h u s a f t e r d i s c o n n e c t i o n o f t h e d o r s a l a o r t i c c a t h e t e r f r o m t h e manometer, b l o o d was a l l o w e d t o f l o w up t h e t u b i n g u n d e r i t s own p r e s s u r e , t h e r e b y f o r c i n g o u t t h e s a l i n e . T h e f i r s t 3 r e d d r o p s o f f l u i d e m e r g i n g f r o m t h e c a t h e t e r were s i m p l y d i s c a r d e d ( " s p i l l a g e " ) , a n d t h e b l o o d s a m p l e c o l l e c t e d . T h e n t h e c a n n u l a was r e c o n n e c t e d t o t h e p r e s s u r e t r a n s d u c e r and s a l i n e s l o w l y r e i n j e c t e d u n t i l t h e b l o o d i n t h e t u b i n g h a d j u s t d i s a p p e a r e d i n t o t h e t r o u t . B l o o d was t r a n s f e r r e d t o C l a y - A d a m s 0.6 ml g l a s s h e m a t o c r i t t u b e s a n d s p u n a t 13000 it G f o r 10 m i n u t e s ; hemat-o c r i t s w e r e r e a d d i r e c t l y f r o m t h e c e n t r i f u g e t u b e s . The s u p e r n a t a n t p l a s m a was a s p i r a t e d i n t o s m a l l p o l y e t h y l e n e v i a l s . A s m a l l p o r t i o n o f t h e p l a s m a (20 uL) f r o m t e r m i n a l s a m p l e s was a n a l y z e d f o r w a t e r c o n t e n t w i t h a G o l d b e r g R e f r a c t o m e t e r ( A m e r i c a n O p t i c a l TS m e t e r ) . T h i s d e v i c e m e a s u r e d r e f r a c t i v e i n d e x w h i c h c o u l d be c o n v e r t e d t o p e r c e n t p l a s m a w a t e r t h r o u g h t a b l e s s u p p l i e d w i t h t h e i n s t r u m e n t ; The s a m p l e s were t h e n f r o z e n and s t o r e d a t - 1 2 ° C . u n t i l f u r t h e r a n a l y s i s . ( i i i ) U r i n e S a m p l e s . U r i n e p r o d u c t i o n was m e a s u r e d o v e r t h e 1 o r 2 h o u r e x p e r i m e n t a l p e r i o d s . I n some e x p e r i m e n t s , t h e c a t h e t e r , a l t h o u g h p a t e n t , was a p p a r e n t l y o c c l u d e d ; u r i n e p r o d u c t i o n d a t a f r o m t h e s e f i s h w ere r e j e c t e d . None o f t h e s e t r o u t e x h i b i t e d symptoms ( u r o g e n i t a l d i s t e n s i o n , h i g h t i s s u e w a t e r l e v e l s ) c h a r a c t e r i s t i c o f c h r o n i c u r i n a r y o c c l u s i o n ( s e e S e c t i o n I I ) . I t was t h e r e f o r e a ssumed t h a t c a n n u l a f a i l u r e was r e c e n t and p r o b a b l y a s s o c i a t e d w i t h t h e s u c t i o n o f s i p h o n d r a i n a g e s t a r t e d a t t h e b e g i n n i n g o f t h e e x p e r i m e n t . On t h i s b a s i s , d a t a on a l l o t h e r p a r a m e t e r s f o r t h e s e a n i m a l s were a c c e p t e d . C o n t a m i n a t i o n o f t h e u r i n e s a m p l e w i t h p r e -e x p e r i m e n t a l p r o d u c t i o n f r o m t h e d e a d s p a c e o f t h e c a n n u l a (0.35 ml) r e n d e r e d i o n i c a n a l y s e s u n i n f o r m a t i v e . However, 22 a s s a y o f Na i n u r i n e f r o m a few e x p e r i m e n t s d e m o n s t r a t e d t h a t r e n a l e x c r e t i o n o f t h e r a d i o i s o t o p e was n e g l i g i b l e a n d t h e r e f o r e h a d no e f f e c t on f l u x r a t e and s o d i u m s p a c e d e t e r -m i n a t i o n s . ( i v ) T i s s u e S a m p l e s . A n a e s t h e t i z a t i o n o f t h e t r o u t w i t h MS 222 p r i o r t o s a c r i f i c e was p e r f o r m e d i n an a t t e m p t t o m a i n t a i n any p h y s i o l o g i c a l d i f f e r e n c e i n t i s s u e s a m p l e s 32 r e s u l t i n g f r o m d i f f e r e n c e s i n e x p e r i m e n t a l t r e a t m e n t s . E x t r e m e h y p e r - a c t i v i t y a s s o c i a t e d w i t h h a n d l i n g i n n o r m a l t r o u t c o u l d w e l l h a v e e l i m i n a t e d c h a r a c t e r i s t i c s d i s t i n c t i v e o f t h e r e s t i n g s t a t e o r r e c o v e r y c o n d i t i o n s . A f t e r r e m o v a l f r o m t h e w a t e r a n d s t u n n i n g , t h e f i s h was q u i c k l y r i n s e d w i t h f r e s h w a t e r an d d r i e d w i t h p a p e r t o w e l s . T h r e e p o r t i o n s ( a p p r o x -i m a t e l y 1.5 g e a c h ) o f d o r s a l e p a x i a l m u s c l e were e x c i s e d f r o m t h e r i g h t s i d e o f t h e t r o u t b e l o w t h e d o r s a l f i n . Any s a m p l e s v i s i b l y c o n t a m i n a t e d w i t h l a t e r a l l i n e r e d m u s c l e o r s k i n w e r e d i s c a r d e d . I n e a r l y e x p e r i m e n t s , e a c h p i e c e o f t i s s u e was i m m e d i a t e l y t r a n s f e r r e d t o a t a r e d a l u m i n u m d i s h a n d w e i g h e d t o .1 mg a c c u r a c y . I n l a t e r r u n s , a l l t h r e e t i s s u e s a m p l e s f r o m an i n d i v i d u a l f i s h w e r e i m m e d i a t e l y s e a l e d i n a s m a l l p o l y -e t h y l e n e v i a l and l e f t f o r 20 - 30 m i n u t e s b e f o r e s e p a r a t i o n a n d w e i g h i n g . T e s t s showed t h a t i d e n t i c a l r e s u l t s were o b t a i n e d w i t h t h e two m e t h o d s . T i s s u e s were d r i e d a t 1 0 3 ° C . f o r 72 h o u r s an d w a t e r c o n t e n t s c a l c u l a t e d b y w e i g h t d i f f e r e n c e . The d i s h e s o f d r i e d t i s s u e w e r e t h e r e a f t e r s t o r e d i n a c l o s e d c o n t a i n e r f o r l a t e r i o n i c a n a l y s i s . ( v ) P h y s i c a l M e a s u r e m e n t s o f t h e F i s h . I o n i c f l u x r a t e s o f t h e g i l l s s h o u l d t h e o r e t i c a l l y be p r o p o r t i o n a l t o t h e s u r f a c e a r e a i m p l i c a t e d ; o v e r a l i m i t e d r a n g e , g i l l a r e a may b e c o n s i d e r e d p r o p o r t i o n a l t o b o d y w e i g h t . I t i s c u s t o m a r y t o e x p r e s s b r a n c h i a l f l u x r a t e s on a p e r w e i g h t b a s i s f o r a f a i r l y homogeneous s e t o f f i s h . A c c u r a t e and s y s t e m a t i c d e t e r m i n a t i o n s o f b o d y w e i g h t w e r e t h e r e f o r e n e c e s s a r y . A f t e r t i s s u e d i s s e c t i o n , t h e c a r c a s s was c a r e f u l l y r e d r i e d a n d w e i g h e d w i t h i n 10 m i n u t e s o f t h e e n d o f t h e e x p e r i m e n t . 33 A c o r r e c t i o n f a c t o r (2 x t h e w e i g h t o f r e m o v e d t i s s u e ) was a d d e d t o g i v e a f i n a l w e i g h t . I n o r d e r t o t e s t w h e t h e r t h e d e g r e e o f b o d y d e v e l o p m e n t ( a n d t h e r e f o r e t h e b o d y w e i g h t t o g i l l a r e a r a t i o ) was s i m i l a r among d i f f e r e n t t r e a t m e n t g r o u p s , r e c o r d s o f l e n g t h , f o r k l e n g t h , a n d maximum d e p t h , were a l s o t a k e n . The m e a s u r e m e n t s p e r m i t t e d c a l c u l a t i o n o f t h e c o -e f f i c i e n t o f c o n d i t i o n , an e x p r e s s i o n o f " p l u m p n e s s " (Toews, 1969) f o r e a c h t r o u t . C o e f f i c i e n t o f C o n d i t i o n = 100 x Body W e i g h t (g) 3 ( F o r k L e n g t h ) (cm) 4. A n a l y t i c a l P r o c e d u r e s 22 ( a ) Na C o n c e n t r a t i o n . ( i ) W a t e r . D u p l i c a t e o r t r i p l i c a t e 1.0 ml a l i q u o t s o f e a c h w a t e r s a m p l e were d r i e d on p l a n c h e t s and c o u n t e d f o r P e m i s s i o n i n a N u c l e a r - C h i c a g o M o d e l 470 g a s f l o w d e t e c t o r e q u i p p e d w i t h an a u t o m a t i c s a m p l e c h a n g e r a n d d e c a d e s c a l e r . A l l s a m p l e s f o r r a d i o a c t i v i t y a n a l y s i s w e r e c o u n t e d 3 t i m e s f o r 30 m i n u t e s / 1 0 , 0 0 0 c o u n t s . ( i i ) P l a s m a . S i n g l e 50 o r 100 uL a l i q u o t s o f e a c h p l a s m a s a m p l e w e r e d i l u t e d w i t h 1.0 ml o f w a t e r on p l a n c h e t s , a n d t h e n s i m i l a r l y c o u n t e d a n d d r i e d . S e l f a b s o r p t i o n r e s u l t i n g f r o m t h e s m a l l amounts o f s o l i d m a t e r i a l i n t h e p l a s m a was i n s i g n i f i c a n t . ( i i i ) T i s s u e . To a v o i d d e r i v a t i o n o f s e l f - a b s o r p t i o n c o r r e c t i o n f a c t o r s f o r a v a r i e t y o f t i s s u e w e i g h t s , i t was n e c e s s a r y t o c o u n t t h e same amount o f m a t e r i a l (75 - 85 mg) i n e a c h p l a n c h e t . D r i e d t i s s u e s a m p l e s were i n d i v i d u a l l y g r o u n d t o a f i n e powder w i t h a m o r t a r a n d p e s t l e . D u r i n g t h e p e r i o d o f s t o r a g e , t h e s a m p l e s h a d r e h y d r a t e d b y 10 - 1 5 % o f t h e i r t r u e d r y w e i g h t . T h u s 85 - 95 mg amounts o f p o w d e r e d t i s s u e w e r e w e i g h e d i n t o t a r e d p l a n c h e t s and r e d r i e d a t 1 0 3 ° C . f o r 12 h o u r s . The p l a n c h e t s w e r e t h e n r e w e i g h e d ; o n l y t h o s e s a m p l e s w i t h a t r u e d r y w e i g h t w i t h i n t h e r a n g e o f 75 - 85 mg w e r e a c c e p t e d . R e j e c t e d s a m p l e s were a p p r o p r i a t e l y c o r r e c t e d a n d t h e d e s s i c a t i o n p r o c e s s r e p e a t e d u n t i l a c c e p t a b l e v a l u e s w e r e o b t a i n e d . One ml o f w a t e r was t h e n a d d e d t o e a c h p l a n c h e t i n o r d e r t o o b t a i n an e v e n d i s t r i b u t i o n o f m a t t e r o v e r t h e e n t i r e s u r f a c e a r e a ; t h e r e s u l t a n t p a s t e was m i x e d t o a f i n e s l u r r y w i t h a n e e d l e . A f t e r s l o w d r y i n g u n d e r a h e a t lamp t o a v o i d c r a c k i n g and f l a k i n g o f t h e powder s u r f a c e , t h e p l a n c h e t s w e r e c o u n t e d as a b o v e . T r i p l i c a t e a l i q u o t s w e r e a n a l y s e d f o r e a c h e x p e r i m e n t . A c o r r e c t i o n f a c t o r (x 1.4661) f o r s e l f - a b s o r p t i o n o f e m i s s i o n s b y t h e t i s s u e s was d e t e r m i n e d 22 b y a s s a y i n g known amounts o f Na w h i c h h a d b e e n i n c u b a t e d a n d d r i e d w i t h 75 - 85 mg o f p o w d e r e d u n l a b e l l e d d o r s a l e p a x i a l m u s c l e . I n a d d i t i o n , i t was n e c e s s a r y t o a p p l y a p p r o p r i a t e c o r r e c t i o n s f o r r a d i o a c t i v e d e c a y a n d e f f i c i e n c y c h a n g e o f t h e c o u n t e r t o t h e r e s u l t s as t i s s u e s a m p l e s were c o u n t e d 9 - 1 2 m onths a f t e r t h o s e o f p l a s m a and w a t e r f r o m a p a r t i c u l a r e x p e r i m e n t . (b) T o t a l S odium C o n c e n t r a t i o n W a t e r . The s o d i u m c o n c e n t r a t i o n o f e x t e r n a l w a t e r s a m p l e s was a s s a y e d b y f l a m e e m i s s i o n p h o t o m e t r y a t 5890 & a g a i n s t a p p r o p r i a t e d i l u t i o n s o f a c o m m e r c i a l l y p r e p a r e d s t a n d a r d ( H a r l e c o ) . As t h e a c t u a l c h a n g e s i n s o d i u m l e v e l s i n a 6 L v o l u m e c a u s e d b y a 200 g t r o u t o v e r 15 m i n u t e i n t e r -v a l s w e r e e x t r e m e l y s m a l l , d i l u t i o n o f a l l s a m p l e s t o a common c o n c e n t r a t i o n r a n g e was i m p r a c t i c a l . Two d i f f e r e n t m e t h o d s o f a n a l y s i s were a p p l i e d , a s d e t e r m i n e d b y t h e p r o p e r t i e s o f t h e two d i f f e r e n t p h o t o m e t e r s u s e d i n t h i s s t u d y . S a m p l e s f r o m t h e r e s t i n g s t a t e a n d a c t i v e e x p e r i m e n t s w e r e a s s a y e d on a U n i c a m M o d e l Sp 900A F l a m e E m i s s i o n / A t o m i c A b s o r p t i o n S p e c t a p h o t o m e t e r . O v e r t h e r a n g e 0 - 3.50 u g N a h / m l , i t was p o s s i b l e t o c a l i b r a t e t h e i n s t r u m e n t o v e r 0.50 ug/ml i n t e r v a l s ( e . g . 1.75 - 2.25 u g N a + / m l ) b r a c k e t i n g t h e c o n c e n -t r a t i o n s o f e x p e r i m e n t a l s a m p l e s . A few s a m p l e s w i t h a c o n -c e n t r a t i o n g r e a t e r t h a n 3.50 u g N a + / m l wer e d i l u t e d 1/2 w i t h d i s t i l l e d w a t e r a n d s i m i l a r l y r e a d . B e c a u s e o f m a r k e d i n -s t a b i l i t y o f t h e i n s t r u m e n t i n t h i s mode o f o p e r a t i o n , m u l t i p l e d e t e r m i n a t i o n s on e a c h unknown were p e r f o r m e d a t l e s s t h a n 5 0 % s c a l e d e f l e c t i o n . S a m p l e s f r o m t h e r e c o v e r y e x p e r i m e n t s w e r e a n a l y s e d on t h e e m i s s i o n mode o f a T e c h t r o n M o d e l AA 120 A t o m i c A b s o r p t i o n S p e c t r o p h o t o m e t e r . O p e r a t i o n o f t h e i n s t r u m e n t a t r a n g e s e x c l u s i v e o f 0 ug N a + / m l was n o t f e a s i b l e . T h u s t h e p h o t o m e t e r was c a l i b r a t e d o v e r i n t e r v a l s o f 0 - 1.00, 0 - 2.00, a n d 0 - 3.00 u g N a + / m l , w i t h i c o n s e q u e n t l o s s o f a c c u r a c y i n t h e h i g h e r c o n c e n t r a t i o n r a n g e s . However t h i s f a u l t was p a r t i a l l y c o m p e n s a t e d f o r b y t h e e x t r e m e s t a b i l i t y a n d r e p r o d u c i b i l i t y o f d e t e r m i n a t i o n s e v e n a t n e a r l y m a x i m a l s c a l e d e f l e c t i o n s . E a c h unknown was r e a d t w i c e ; t h o s e e x -c e e d i n g t h e - h i g h e s t c a l i b r a t i o n r a n g e were a g a i n d i l u t e d b y two. O v e r a l l , t h e a c c u r a c y o f t h e two t e c h n i q u e s a p p e a r e d t o be c o m p a r a b l e , b u t t h e l a t t e r was f a r more e f f i c i e n t . ( i i ) P l a s m a . T r i p l i c a t e d i l u t i o n s (1 uL i n 6.00 m i s o f d i s t i l l e d w a t e r ) o f e a c h p l a s m a s a m p l e were a s s a y e d i n t h e 0 - 1.00 ug N a + / m l c a l i b r a t i o n r a n g e on e i t h e r f l a m e p h o t o m e t e r . E a c h d i l u t i o n was r e a d 2 - 3 t i m e s . I t s h o u l d be n o t e d t h a t f r e e z i n g o f p l a s m a may r e s u l t i n p a r t i a l p r e c i p i t a t i o n o f p r o t e i n s , p r o d u c i n g a s a m p l e w h i c h i s s t r i c t l y n e i t h e r p l a s m a n o r s e r u m . However t e s t s h a v e shown t h a t s o d i u m c o n c e n t r a t i o n s o f t h e f l u i d a r e n o t s i g n i f i c a n t l y c h a n g e d b y t h e f r e e z i n g p r o c e s s (Toews, p e r s o n a l c o m m u n i c a t i o n ) ; f o r t h e s a k e o f c o n -v e n i e n c e , t h e t e r m " p l a s m a " c o n c e n t r a t i o n i s u s e d t h r o u g h o u t t h i s t h e s i s f o r d e t e r m i n a t i o n s on f r o z e n s a m p l e s . ( i i i ) T i s s u e . S i n g l e 115 mg a l i q u o t s o f e a c h p o w d e r e d m u s c l e s a m p l e were w e i g h e d i n t o s m a l l t a r e d p o l y e t h y l e n e v i a l s . T h e c o n t a i n e r s were h e a t e d a t 7 0 ° C . f o r 24 h o u r s a n d r e w e i g h e d t o o b t a i n t r u e d r y w e i g h t s . E x a c t l y 1.0 ml o f c o n c e n t r a t e d HNO^ was t h e n a d d e d , a n d t h e s a m p l e s i n c u b a t e d f o r 48 h o u r s a t room t e m p e r a t u r e . T r i p l i c a t e 50 uL a l i q u o t s were d i l u t e d t o 10.0 m i s a n d a s s a y e d o n t h e T e c h t r o n f l a m e p h o t o m e t e r o v e r a 0 - 50 uEq- N a + / L c a l i b r a t i o n r a n g e . Toews (1966) h a s shown t h a t t h e h i g h c o n c e n t r a t i o n o f p o t a s s i u m i n t r o u t m u s c l e e n h a n c e s s o d i u m f l a m e e m i s s i o n b y as much as 15%. T h e r e f o r e f i n a l d i l u t i o n s o f b o t h s t a n d a r d s a n d unknowns c o n t a i n e d a 200 ug K + / m l swamp t o e l i m i n a t e t h i s e f f e c t . 5. C a l c u l a t i o n s (a) S o d i u m F l u x R a t e s M e a s u r e m e n t s o f t h e d e c l i n e i n r a d i o a c t i v i t y and c h a n g e i n s o d i u m c o n c e n t r a t i o n o f t h e e x t e r n a l medium o v e r t h e one h o u r e x p e r i m e n t a l p e r i o d a l l o w e d c a l c u l a t i o n o f s o d i u m i n f l u x , e f f l u x , a n d n e t f l u x a c r o s s t h e e x t e r n a l s u r f a c e o f t h e t r o u t . M u l t i p l i c a t i o n o f t h e c o n c e n t r a t i o n o f t o t a l 22 s o d i u m (ug/ml) a n d Na (cpm/ml) by t h e v o l u m e o f w a t e r i n t h e chamber ( a f t e r a p p r o p r i a t e c o r r e c t i o n f o r s a m p l i n g d e f i c i t s ) 22 y i e l d e d a b s o l u t e amounts o f t o t a l s o d i u m (Na e x t ) and Na (Q) i n t h e e x t e r n a l medium a t any one t i m e . O v e r any t i m e p e r i o d ( A t ) , t h e i n f l u x r a t e ( F i ) o f s o d i u m ( u g / m i n ) i n t o t h e f i s h c o u l d be c a l c u l a t e d f r o m t h e s p e c i f i c a c t i v i t y a n d l o s s i n r a d i o a c t i v i t y (AQ) o f t h e e x t e r n a l medium: A Q F i = " A t (1) Na e x t S i m i l a r l y t h e n e t f l u x r a t e ( F n ) o f s o d i u m o v e r t h e same t i m e i n t e r v a l c o u l d be c o m p u t e d f r o m t h e c h a n g e o f t o t a l s o d i u m (ANa e x t ) i n t h e v / a t e r : Fn = - A N a e x t (2) A t T h u s t h e n e t f l u x was p o s i t i v e when e x t e r n a l N a + c o n c e n t r a t i o n d i m i n i s h e d . F i n a l l y t h e e f f l u x r a t e ( F o ) was c a l c u l a t e d b y d i f f e r e n c e : Fo = F i - F n (3) F l u x r a t e s h a v e b e e n e x p r e s s e d as ug N a + / 1 0 0 g b o d y w e i g h t / m i n . I t s h o u l d b e n o t e d t h a t a t no t i m e d u r i n g t h e one h o u r e x p e r i -m e n t a l p e r i o d s d i d t h e i n t e r n a l s p e c i f i c a c t i v i t y o f s o d i u m r e p r e s e n t more t h a n 3.5% o f t h e e x t e r n a l v a l u e , t h e r e b y 22 r e n d e r i n g b a c k f l u x o f Na i n t o t h e w a t e r i n s i g n i f i c a n t . 22 22 (b) A p p a r e n t Volume o f D i s t r i b u t i o n o f Na o r Na S p a c e T h i s p a r a m e t e r i s a t h e o r e t i c a l l y d e r i v e d m e a s u r e o f t h e d i s t r i b u t i o n o f t h e r a d i o i s o t o p e w i t h i n t h e o r g a n i s m . I t 22 i s d e f i n e d a s t h e v o l u m e ( m l / l O O g b o d y w e i g h t ) o c c u p i e d b y Na i n t h e o r g a n i s m when u n i f o r m l y d i s t r i b u t e d a t t h e same c o n c e n -t r a t i o n a s t h a t o f t h e p l a s m a . The r a d i o s o d i u m s p a c e ( V i n t ) 38 a t a p a r t i c u l a r t i m e was c a l c u l a t e d f r o m t h e m e a s u r e d c o n -22 22 c e n t r a t i o n o f Na i n t h e p l a s m a (Na /ml p t ) a n d t h e known amount o f r a d i o a c t i v i t y i n t h e t r o u t (Qo - Q ) . Qo r e p r e s e n t s 22 t h e amount o f Na (cpm) a d d e d t o t h e e x t e r n a l medium a t t i m e z e r o . V i n t = Qo - Q (4) 22 Na /ml p t ( c ) F a t e o f Sod i u m T a k e n up f r o m t h e E x t e r n a l E n v i r o n m e n t 22 T h e Na s p a c e p r o v i d e s a m e a s u r e o f d i s p e r s a l o f i n -f l u x e d s o d i u m i n t h e o r g a n i s m , b u t r e v e a l s no c a u s e s f o r t h e o b s e r v e d d i s t r i b u t i o n . F o r e x a m p l e , a r e l a t i v e l y h i g h d i s -t r i b u t i o n v o l u m e c o u l d r e s u l t f r o m one o r more o f t h e f o l l o w i n g f a c t o r s : a r a p i d e x c h a n g e o f p l a s m a s o d i u m w i t h t i s s u e s o d i u m , a l o c a l i z e d s o d i u m " s i n k " w i t h i n t h e s y s t e m , o r a l a r g e p l a s m a v o l u m e . I n o r d e r t o i n v e s t i g a t e d i f f e r e n c e s i n r a d i o -s o d i u m d i s t r i b u t i o n v o l u m e among t h e t r e a t m e n t g r o u p s , t h e f a t e o f s o d i u m i o n s t a k e n up f r o m t h e e x t e r n a l e n v i r o n m e n t was t r a c e d b y means o f t h e r a d i o i s o t o p e i n b o t h p l a s m a a n d t i s s u e . ( i ) P l a s m a . A t e a c h b l o o d s a m p l i n g t i m e , t h e c o n c e n -t r a t i o n i n p l a s m a o f s o d i u m i o n s t r a n s p o r t e d f r o m t h e e x t e r n a l medium (Na p t ) was e s t i m a t e d f r o m t h e m e a s u r e d c o n c e n t r a t i o n 22 o f Na i n p l a s m a a n d t h e a v e r a g e e x t e r n a l s p e c i f i c a c t i v i t y o v e r t h e e x p e r i m e n t a l p e r i o d up t o t h a t t i m e . Na e x t Q r e p r e s e n t s t h e t o t a l s o d i u m c o n t e n t o f t h e w a t e r a t t i m e z e r o . Na p t = 2 x N a 2 2 / m l p t (5) Qo Q Na e x t -Na e x t o ( i i ) T i s s u e . S i m i l a r l y t h e l e v e l o f s o d i u m i o n s i n d o r s a l e p a x i a l m u s c l e w h i c h h a d o r i g i n a t e d f r o m t h e e x t e r n a l w a t e r d u r i n g t h e e x p e r i m e n t a l p e r i o d ( Na t t ) c o u l d b e a p p r o x i -m a t e d f r o m t h e r a d i o a c t i v i t y p e r gram o f t h e t e r m i n a l t i s s u e 22 s a m p l e (Na / g t t ) Na t t = 2 x N a 2 2 / q t t (6) Qo + Q Na e x t Na e x t o I n t h i s c a s e , Q must r e p r e s e n t t h e e x t e r n a l s p e c i f i c Na e x t a c t i v i t y a t 60 m i n u t e s . I t s h o u l d be e m p h a s i z e d t h a t Na t t m e r e l y e s t i m a t e s t h e c o n c e n t r a t i o n i n m u s c l e o f s o d i u m w h i c h h a d b e e n i n f l u x e d f r o m t h e e n v i r o n m e n t o v e r t h e 60 m i n u t e p e r i o d ; t h e v a l u e i s i n no way an a b s o l u t e m e a s u r e o f t h e i n -c o r p o r a t i o n o f p l a s m a s o d i u m i o n s i n t o t i s s u e , n o r e v e n n e c e s s a r i l y p r o p o r t i o n a l t o t h i s p a r a m e t e r . Once e x t e r n a l s o d i u m h a s b e e n t a k e n up b y t h e g i l l s i n t o t h e b l o o d s t r e a m , 22 i t s s p e c i f i c a c t i v i t y ( Na /Na t o t a l ) w i l l b e d r a s t i c a l l y 2 3 r e d u c e d b y d i l u t i o n w x t h t h e l a r g e number o f Na i o n s i n p l a s m a 22 However t h e amount o f Na i n c o r p o r a t e d i n t i s s u e s h o u l d s t i l l b e p r o p o r t i o n a l ( i n t h e r a t i o o f t h e a v e r a g e e x t e r n a l s p e c i f i c a c t i v i t y ) t o t h e t o t a l i n c o r p o r a t i o n o f s o d i u m i o n s f r o m t h e w a t e r . (d) E x t r a c e l l u l a r F l u i d V olume ( E . C . F . V . ) E x t r a c e l l u l a r f l u i d v o l u m e may be e s t i m a t e d f r o m t h e v o l u m e o f d i s t r i b u t i o n o f t o t a l b o d y s o d i u m when a p p r o p r i a t e c o r r e c t i o n s a r e a p p l i e d f o r t h e h e t e r o g e n e o u s d i s t r i b u t i o n o f t h e i o n i n t h e o r g a n i s m . E.C.F.V. c a l c u l a t e d i n t h i s manner i s known as s o d i u m s p a c e , b u t s h o u l d n o t be c o n f u s e d w i t h r a d i o s o d i u m s p a c e . The f o l l o w i n g f o r m u l a , as g i v e n b y M a n e r y (1954) was u t i l i z e d f o r c o m p u t a t i o n o f E.C.F.V.: Na s p a c e = Na t x ( H 2 0 ) p (7) Na p x R 40 Where: Na t = t i s s u e N a + c o n c e n t r a t i o n i n mEq/kg wet t i s s u e ( H „ 0 ) p = p l a s m a w a t e r c o n c e n t r a t i o n i n m l / k g wet p l a s m a Na p = p l a s m a Na c o n c e n t r a t i o n i n mEq/L p l a s m a R = G i b b s Donnan r a t i o f o r Na U n f o r t u n a t e l y t h e G i b b s Donnan r a t i o f o r N a + h a s n o t y e t b e e n e s t a b l i s h e d f o r f r e s h w a t e r t e l e o s t t i s s u e , s o t h e v a l u e R = 0.942, o b t a i n e d f r o m mammalian s t u d i e s , was u s e d . 6. P r e s e n t a t i o n o f D a t a (a ) O r g a n i z a t i o n I n a s t u d y o f t h i s n a t u r e , i n v o l v i n g s i m u l t a n e o u s m e a s u r e m e n t o f s e v e r a l p a r a m e t e r s a n d t h e c o l l e c t i o n o f m u l t -i p l e s a m p l e s , i t was i n e v i t a b l e t h a t some d a t a s h o u l d b e l o s t . S u c h l o s s e s o c c u r r e d b o t h d u r i n g t h e e x p e r i m e n t ( e . g . c a n n u l a o c c l u s i o n o r t r a n s d u c e r f a i l u r e ) a n d i n t h e l a t e r p r o c e s s i n g o f s a m p l e s ( e . g . c o n t a m i n a t i o n , d i l u t i o n e r r o r s ) . Y e t i t seemed u n r e a s o n a b l e t o d i s c a r d a l l d a t a f r o m a p a r t i c u l a r t r o u t on t h e b a s i s o f an a b s e n c e o f one o r two s a m p l e s . T h e r e f o r e t h e f o l l o w i n g scheme was u s e d . W i t h i n e a c h t r e a t m e n t g r o u p , v a l u e s f o r a p a r t i c u l a r p a r a m e t e r a t e a c h m e a s u r e m e n t t i m e were p r e s e n t e d as a mean a c c o m p a n i e d b y N = number o f o b s e r v a t i o n s . E a c h p i e c e o f d a t a a c c e p t a b l e i n i t s own r i g h t was i n c l u d e d i n t h e a v e r a g e , w i t h t h e e x c e p t i o n o f c a s e s w h e re f a i l u r e t o o b t a i n a r e l a t e d s a m p l e w o u l d o b v i o u s l y b i a s t h e i n c l u s i o n o f t h e v a l u e i n q u e s t i o n . F o r e x a m p l e , p l a s m a w a t e r v a l u e s were u s e d f r o m an a n i m a l i n w h i c h t i s s u e s o d i u m c o n c e n t r a t i o n was u n a v a i l a b l e ; h o w e v e r h e m a t o c r i t and p l a s m a s o d i u m v a l u e s were r e j e c t e d f o r a f i s h f r o m w h i c h o n l y two b l o o d s a m p l e s w e r e drawn, f o r 41 t h e n o r m a l s e r i a l s a m p l i n g p r o c e s s was a t l e a s t p a r t i a l l y r e s -p o n s i b l e f o r t h e o b s e r v e d c h a n g e s i n t h e s e f a c t o r s w i t h t i m e i n o t h e r t r o u t . ( b) S t a t i s t i c a l A n a l y s e s The f o l l o w i n g t e c h n i q u e s h a v e b e e n a p p l i e d i n a l l t h r e e s e c t i o n s o f t h i s s t u d y . D a t a ha)» £ g e n e r a l l y b e e n e x p r e s s e d as a mean a c c o m p a n i e d b y t h e N number a n d t h e s t a n d a r d e r r o r o f t h e mean. P o s s i b l e r e l a t i o n s h i p s b e t w e e n p a r a m e t e r s h a v e b e e n t e s t e d b y t h e c a l c u l a t i o n o f s i m p l e c o r r e l a t i o n c o e f f i c i e n t s . S t r a i g h t l i n e s h a v e b e e n f i t t e d t o d a t a p o i n t s b y r e g r e s s i o n l i n e s c o m p u t e d by t h e m e t h o d o f l e a s t s q u a r e s . F o r some p a r a -m e t e r s , s e t s o f d a t a w e r e s u b j e c t e d t o a one way a n a l y s i s o f v a r i a n c e . The v a l u e s o f F o b t a i n e d f r o m t h e a n a l y s e s a n d t h e i r l e v e l s o f s i g n i f i c a n c e a r e p r e s e n t e d . Means w i t h i n e a c h t r e a t m e n t g r o u p were t h e n c o m p a r e d f o r s i g n i f i c a n t d i f f e r e n c e s a t t h e 5% p r o t e c t i o n l e v e l b y u s e o f a m o d i f i c a t i o n o f D u n c a n ' s New M u l t i p l e Range T e s t ( D u n c a n , 1 9 5 5 ) . D u n c a n ' s t e s t i s d e s i g n e d f o r t h e a n a l y s i s o f s e t s o f d a t a i n w h i c h e a c h m e a s u r e -ment c a t e g o r y c o n t a i n s an e q u a l number o f r e p l i c a t e s , a c o n d i t i o n w h i c h d o e s n o t a p p l y i n t h e p r e s e n t s t u d y . The e x t e n s i o n o f t h e New M u l t i p l e Range T e s t f o r u n e q u a l numbers o f r e p l i c a t i o n s , p r o p o s e d b y K r a m e r ( 1 9 5 6 ) , h a s b e e n u t i l i z e d . The t e c h n i q u e i s e s s e n t i a l l y c o n s e r v a t i v e ; " i f t h e number o f r e p l i c a t e s d i f f e r s g r e a t l y , t h e r e w i l l be an i n c r e a s e d p r o b a b i l i t y o f a s i g n i f i -c a n t d i f f e r e n c e w i t h i n a s u b s e t o f r a n k e d means c l a s s e d as homogeneous b y t h i s t e s t " . ( K r a m e r , 1 9 5 6 ) . I n l e g e n d s f o r f i g u r e s , a s i n g l e l i n e u n d e r - s c o r e s s u b s e t s o f means w i t h i n w h i c h i t h a s n o t b e e n p o s s i b l e t o d e m o n s t r a t e s i g n i f i c a n t d i f f e r e n c e s . S i g n i f i c a n c e l e v e l s o f d i f f e r e n c e b e t w e e n comp-a r a b l e means o f d i f f e r e n t t r e a t m e n t g r o u p s h a v e b e e n a s c e r -t a i n e d b y a p p l i c a t i o n o f t h e " S t u d e n t ' s " t - t e s t . U n l e s s o t h e r w i s e s t a t e d , s i g n i f i c a n c e h a s b e e n assumed a t t h e .05 l e v e l . RESULTS AND DISCUSSION I A. The E f f e c t o f C h a s i n g on V e n t i l a t o r y and C a r d i o v a s c u l a r  P a r a m e t e r s C h a s i n g o f t r o u t i n a chamber o n l y s l i g h t l y l o n g e r t h a n t h e a n i m a l ' s b o d y i n i t i a l l y a p p e a r e d t o be a f a r f r o m s a t i s f a c t o r y m e t h o d f o r i n d u c i n g a c t i v i t y , b u t was t h e o n l y t e c h n i q u e c o m p a t i b l e w i t h s i m u l t a n e o u s s o d i u m f l u x r a t e m e a s u r e m e n t s . I t was, t h e r e f o r e , c r i t i c a l l y i m p o r t a n t t o t h e m a j o r p a r t o f t h i s s t u d y , t h e i n v e s t i g a t i o n o f s o d i u m b a l a n c e d u r i n g e x e r c i s e , t o d e m o n s t r a t e t h a t t h e p r o c e d u r e a d o p t e d d i d i n f a c t c a u s e r e a l d i f f e r e n c e s i n c a r d i o - r e s p i r a t o r y f u n c t i o n b e t w e e n e x p e r i m e n t a l g r o u p s o f f i s h , a n d t h a t t h e s e c h a n g e s were d i s t i n c t l y r e p r e s e n t a t i v e o f r e s t i n g s t a t e , swimming, a n d r e c o v e r y c o n d i t i o n s . Two m e t h o d s o f p r e s e n t a t i o n h a v e b e e n u t i l i z e d f o r e x p r e s s i o n o f c a r d i o v a s c u l a r a n d r e s p i r a t o r y d a t a . F i g u r e s 5 , 6 , 7 , and 8 p r e s e n t t h e r e s u l t s as means o f r e a l v a l u e s . I n T a b l e I , on t h e o t h e r h a n d , d a t a a r e s u m m a r i z e d a t s e l e c t e d s a m p l e t i m e s i n t e r m s o f "% r o u t i n e " v a l u e s ( c f . D a v i s , 1 9 6 8 ) . The t e r m " r o u t i n e " i s h e r e u s e d i n a s e n s e h o m o l o g o u s t o B r e t t ' s (1962) d e s c r i p t i o n o f t h e m e t a b o l i c r a t e o f f i s h u n d e r -g o i n g c o n t i n u o u s r e c o r d i n g i n t h e l a b o r a t o r y s i t u a t i o n ; d e t e r m i n a t i o n s t a k e n p r i o r t o z e r o t i m e h a v e b e e n c o n s i d e r e d " r o u t i n e " . E x p r e s s i o n o f r e s u l t s i n t h i s manner i s a d v a n t -a g e o u s i n c o n s i d e r i n g c h a n g e s i n m e a s u r e d p a r a m e t e r s f o r a s p e c i f i c f i s h r e l a t i v e t o t h e v a l u e f o r t h a t p a r t i c u l a r a n i m a l i n a q u i e s c e n t s t a t e ; t r e n d s o b s c u r e d b y v a r i a b i l i t y i n t h e d a t a may t h e r e f o r e become a p p a r e n t . I t w i l l be n o t e d t h a t 44 T a b l e I . V e n t i l a t o r y and c a r d i o v a s c u l a r r e s p o n s e s d u r i n g the r e s t i n g , a c t i v e , and r e c o v e r y experiments i n terms o f mean "% r o u t i n e " v a l u e s . 5 o r 65 minutes H e a r t r a t e : r e s t a c t i v e 104.25 109.32 r e c o v e r y 108.14 30 o r 90 minutes 103.00 120.19 103.00 60 o r 120 minutes 107.44 117.16 105.97 D o r s a l a o r t i c b l o o d p r e s s u r e : r e s t 98.06 a c t i v e 106.28 r e c o v e r y 87.92 93.86 101.12 94.41 92.08 103.12 88.93 V e n t i -l a t i o n r a t e : r e s t 99.86 a c t i v e 110.35 r e c o v e r y 101.85 99.73 109.38 98.41 99.35 107.10 96.21 B u c c a l r e s t 108.40 102.52 92.52 p r e s s u r e a m p l i - a c t i v e 141.96 169.28 169.44 tude: r e c o v e r y 132.26 102.45 104.11 45 F i g u r e 4 T y p i c a l p r e s s u r e r e c o r d i n g s from the d o r s a l a o r t a and b u c c a l c a v i t y o f a rainbow t r o u t o b t a i n e d d u r i n g r e s t , c h a s i n g , and r e c o v e r y i n the p r o t o c o l o f S e c t i o n I . F i s h #U. 235.4 g. Recovery group. DORSAL 50r AORTIC BLOOD PRESSURE (mm Hg ) 25k BUCCAL PRESSURE (mm Hg ) 5i YWYYVYYVVVYVw^^ 10 seconds 0 MINUTES-REST resume chasing ll 30 MINUTES-EXERCISE DORSAL AORTIC BLOOD PRESSURE (mm Hg ) BUCCAL PRESSURE (mm Hg) 50p 25h 0«-cease chasing 60 MINUTES-EXERCISE 120 MINUTES-RECOVERY 46 F i g u r e 5 V a r i a t i o n s i n h e a r t r a t e over the e x p e r i m e n t a l p e r i o d s i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . F i r s t hour v a l u e s f o r r e c o v e r y f i s h were o b t a i n e d d u r i n g t h e i r i n i t i a l c h a s i n g t r e a t m e n t . Means + - 1 s t a n d a r d e r r o r . 80H REST N=7 40 -F-' 80 -z. 2 2^ 6 0 -CD 15 30 4 5 ACTIVE N=9 ,L • = ACTIVE FISH A - RECOVERY FISH -1st HOUR i 60 J U J I— < cn 40-or 8 0 -< UJ 60H 0 15 35T x 4 5 RECOVERY N = 8 __J 60 40 -6 0 75 90 105 120 TIME (MINUTES) 47 " % r o u t i n e " v a l u e s p r e s e n t e d i n T a b l e I c a n n o t be c o m p u t e d f r o m p o i n t s i n F i g s . 5 - 8 ; t h e f o r m e r a r e means o f p e r c e n t a g e s w h i l e t h e l a t t e r w o u l d be p e r c e n t a g e s o f means. The o n s e t o f c h a s i n g was a s s o c i a t e d w i t h i m m e d i a t e i n c r e a s e s i n v e n t i l a t o r y a m p l i t u d e and r a t e , d o r s a l a o r t i c b l o o d p r e s s u r e , and, i n many a n i m a l s , a n o t i c e a b l e s h o r t - t e r m b r a d y c a r d i a c h a n g i n g t o a t a c h y c a r d i a a f t e r 15 - 30 s e c o n d s ( F i g . 4 ) . However b o t h t r a c e s r e m a i n e d h i g h l y e r r a t i c t h r o u g h o u t c h a s i n g , t h e r e b y p r e c l u d i n g s y s t e m a t i c d e t e r m i n -a t i o n s o f r a t e s and p r e s s u r e s d u r i n g a c t u a l e x e r c i s e p e r i o d s . C o n s e q u e n t l y , o n l y v a l u e s e x t r a c t e d f r o m r e c o r d i n g s t a k e n d u r i n g t h e one m i n u t e r e s t i n t e r v a l s i m m e d i a t e l y b e f o r e and a f t e r e a c h b l o o d s a m p l i n g t i m e h a v e b e e n r e p o r t e d . T h e s e v a l u e s a r e p r o b a b l y somewhat l o w e r t h a n t h e mean r a t e s and p r e s s u r e s a t t a i n e d b y e x e r c i s e d f i s h d u r i n g t h e e x p e r i m e n t a l p e r i o d s . H e a r t r a t e ( F i g . 5) r e m a i n e d s t a b l e d u r i n g r e s t , i n c r e a s e d a maximum 2 0% d u r i n g c h a s i n g , and d e c l i n e d t o p r e -e x e r c i s e l e v e l s d u r i n g r e c o v e r y . T h i s c a r d i o a c c e l e r a t i o n i s c o m p a r a b l e t o t h a t (15%) r e c o r d e d i n Salmo g a i r d n e r i d u r i n g t e n m i n u t e s o f m o d e r a t e swimming (up t o 52 c m/sec.) i n a w a t e r t u n n e l ( S t e v e n s and R a n d a l l , 1 9 6 7 a ) . The i n c r e a s e i s f a r s m a l l e r t h a n t h e 40 - 8 0 % t a c h y c a r d i a o b s e r v e d a t f a t i g u e s p e e d s i n m a t u r e s o c k e y e salmon^ O n c h o r y n c h u s n e r k a ^ ( S m i t h e t a l . , 1 9 6 7 ; D a v i s , 1 9 6 8 ) . However, S t e v e n s (1968 b) f o u n d t h a t i m p o s i t i o n o f s e v e r e e x e r c i s e on r a i n b o w t r o u t c o u l d e l i c i t an i n c r e a s e i n c a r d i a c f r e q u e n c y o f no more t h a n 1 5 % . The d i f f e r e n c e i n t h e c a r d i a c r a t e r e s p o n s e t o swimming b e t w e e n t r o u t and s a l m o n i s p r o b a b l y r e l a t e d t o t h e a b s e n c e i n t h e 48 f o r m e r ( S t e v e n s a n d R a n d a l l , 1 9 6 7 a ) , b u t p r e s e n c e i n t h e l a t t e r ( R a n d a l l a n d S t e v e n s , 1 9 6 7 ) o f v a g a l t o n e a t r e s t . S t e v e n s and R a n d a l l (1967 a, b,) c a l c u l a t e d t h a t t h e 15% c a r d i o a c c e l e r a t i o n d u r i n g m o d e r a t e a c t i v i t y i n r a i n b o w s was a s s o c i a t e d w i t h a 4.5 f o l d i n c r e a s e i n c a r d i a c o u t p u t . I t seems p r o b a b l e t h a t s i m i l a r c h a n g e s o c c u r r e d i n c h a s e d f i s h i n t h e p r e s e n t s t u d y r e s u l t i n g i n a u g m e n t a t i o n o f b l o o d f l o w t h r o u g h t h e g i l l s . T h e c a r d i a c o u t p u t o f t h e i s o l a t e d h e a r t o f Salmo g a i r d n e r i c a n be r e l a t e d t o a s e r i e s o f S t a r l i n g c u r v e s a t d i f f e r e n t f i l l i n g p r e s s u r e s a n d c a t e c h o l a m i n e c o n c e n t r a t i o n s o f t h e p e r -f u s i o n f l u i d ; an e l e v a t i o n o f e i t h e r f a c t o r c a u s e s an i n c r e a s e i n o u t p u t ( B e n n i o n , 1 9 6 8 ) . V e n o u s r e t u r n p r o b a b l y i n c r e a s e s d u r i n g swimming, b u t t h e r e a r e as y e t no m e a s u r e s o f v e n o u s f i l l i n g p r e s s u r e s i n v i v o i n t e l e o s t s . Ample s t o r e s o f a d r e n a l i n e a n d n o r a d r e n a l i n e p l u s an as y e t u n i d e n t i f i e d c a t e -c h o l a m i n e ( " c a t e c h o l - 4") h a v e b e e n r e p o r t e d i n t e l e o s t t i s s u e , ( O s t l u n d , 1954; v o n E u l e r a n d Fa.nge,1961; Nakano and T o m l i n s o n , 1967; Gannon and B u r n s t o c k , 1 9 6 9 ) . S i g n i f i c a n t e l e v a t i o n s o f p l a s m a c a t e c h o l a m i n e c o n c e n -t r a t i o n s h a v e b e e n f o u n d i n c o r r e s p o n d e n c e w i t h d i u r n a l a c t i v i t y r h y t h m s i n t h e c h a n n e l c a t f i s h ^ I c t a l u r u s p u n c t a t u s } ( B o e h l k e e t al_.,1967) an d i n r e s p o n s e t o i n d u c e d e x e r c i s e i n t h e r a i n b o w t r o u t (Nakano and T o m l i n s o n , 1 9 6 7 ) . I t seems p r o b a b l e t h a t m o b i l i z a t i o n o f t h e s e hormones i s a t l e a s t p a r t i a l l y r e s p o n s i b l e f o r t h e m a i n t e n a n c e o f h i g h c a r d i a c d e l i v e r y d u r i n g swimming. A r g u m e n t s were p r e s e n t e d i n t h e g e n e r a l i n t r o d u c t i o n t h a t a d r e n a l i n e and n o r a d r e n a l i n e a r e a l s o r e s p o n s i b l e f o r v a s o d i l a t i o n o f t h e b r a n c h i a l c a p i l l a r y n e t w o r k and s t i m u l a t i o n o f l a m e l l a r b l o o d f l o w . I n c r e a s e d p a s s a g e o f 4 9 Figure 6 V a r i a t i o n s i n dorsal a o r t i c blood pressure over the experimental periods i n r e s t i n g , a c t i v e , and recovery groups of t r o u t . F i r s t hour values for recovery f i s h were obtained during t h e i r i n i t i a l chasing treatment. Means - 1 standard e r r o r . Area mean blood pressure = 2 ( d i a s t o l i c ) + 1 s y s t o l i c 3 40 H 30-^ O) I E E UJ or Z> UI UI LU o: Q . Q Q CQ 20 H 10 30-^ 20-g O 10 < 30 H < 8 z < LU Z 20H < LU < 10 o 15 O 60 15 REST N=7 30 45 GO ACTIVE N=8 30 • = ACTIVE FISH A= RECOVERY FISH -1 s t HOUR L 45 60 RECOVERY N=7 75 90 TIME (MINUTES) 105 120 50 b l o o d t h r o u g h t h e s e r e s p i r a t o r y pathv;ays s h o u l d i n t u r n f a c -i l i t a t e o x y g e n an d c a r b o n d i o x i d e e x c h a n g e . I t w o u l d t h e r e f o r e a p p e a r t h a t c a t e c h o l a m i n e s a r e i n s t r u m e n t a l i n e f f e c t i n g c i r -c u l a t o r y a d a p t a t i o n t o t h e i n c r e a s e d m e t a b o l i c demands o f e x e r c i s e . D o r s a l a o r t i c b l o o d p r e s s u r e v a r i e d g r e a t l y b e t w e e n i n d i v i d u a l a n i m a l s b u t t h e mean g e n e r a l l y r e m a i n e d s t a b l e o r f e l l s l i g h t l y o v e r t h e e x p e r i m e n t a l p e r i o d ( F i g . 6 ) . E x p r e s s i o n o f t h e d a t a i n r e l a t i o n t o r o u t i n e v a l u e s ( T a b l e I ) r e v e a l e d t h a t e x e r c i s e d t r o u t m a i n t a i n e d p r e s s u r e s s l i g h t l y a b o v e r e s t i n g l e v e l s d e s p i t e t h e s e r i a l r e m o v a l o f b l o o d demanded b y t h e e x p e r i m e n t a l p r o t o c o l . T h i s r e d u c t i o n i n b l o o d v o l u m e e x p l a i n s t h e p r o g r e s s i v e f a l l i n p r e s s u r e o b s e r v e d i n r e s t i n g a n i m a l s ( T a b l e I ) . S i m i l a r e f f e c t s h a v e b e e n n o t e d i n s a l m o n ( S m i t h e t a l . , 1 9 6 7 ; R a n d a l l and S m i t h , 1 9 6 7 ) , t h e d r o p i n b l o o d p r e s s u r e b e i n g p r o p o r t i o n e d t o t h e v o l u m e w i t h d r a w n . D u r i n g r e c o v e r y , " ^ r o u t i n e " p r e s s u r e s were l e a s t i m m e d i a t e l y a f t e r t e r m i n a t i o n o f c h a s i n g a n d d i d n o t d e c r e a s e i n r e s p o n s e t o f u r t h e r d e p l e t i o n o f c i r c u l a t o r y f l u i d . When a p p r o p r i a t e c o r r e c t i o n s f o r t h e e f f e c t s o f b l o o d s a m p l i n g a r e a p p l i e d t o t h e p r e s s u r e c h a n g e s m e a s u r e d i n t h e p r e s e n t s t u d y , t h e data, f o l l o w t r e n d s s i m i l a r t o t h o s e r e p o r t e d d u r i n g m o d e r a t e e x e r c i s e a n d r e c o v e r y u n d e r more c o n t r o l l e d c o n d i t i o n s ( S t e v e n s a n d R a n d a l l , 1 9 6 7 a; D a v i s , 1 9 6 8 ) ; i n t h e s e s t u d i e s , p r e s s u r e c h a n g e s c o u l d be c o r r e l a t e d w i t h v a r i a t i o n s i n c a r d i a c o u t p u t . B o t h b r e a t h i n g r a t e ( F i g . 7) and b u c c a l p r e s s u r e ( F i g . 8) r e m a i n e d c o n s t a n t i n t h e r e s t i n g g r o u p o f t r o u t . C h a s e d f i s h d e m o n s t r a t e d a s l i g h t p o l y p n e a (10%) and v e r y l a r g e i n c r e a s e s i n b u c c a l p r e s s u r e (70%) ( T a b l e I ) ; t h e s e t r e n d s w e r e 51 Figure 7 V a r i a t i o n s i n v e n t i l a t i o n rate over the experimental periods i n r e s t i n g , a c t i v e , and recovery groups of t r o u t . F i r s t hour values for recovery f i s h were obtained during t h e i r i n i t i a l chasing treatment. Means - 1 standard e r r o r . 9 0 - i 8 OH REST N=10 LU i— ZD 70 -00 LJ 100H DC ZD 9 U X I-ZD O 2 LU CC 9 0 H 80H O o 15 30 15 3 0 4 5 ACTIVE N=11 6 0 • --ACTIVE FISH A= RECOVERY FISH -1st HOUR 4 5 60 O 1 0 0 i Lu 9 0H > 8 0 -RECOVERY N = 11 7 0 -LL 6 0 75 9 0 105 120 TIME (MINUTES) 52 F i g u r e 8 V a r i a t i o n s i n b u c c a l p r e s s u r e amplitude over the e x p e r i m e n t a l p e r i o d s i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . F i r s t hour v a l u e s f o r r e c o v e r y f i s h were o b t a i n e d d u r i n g t h e i r i n i t i a l c h a s i n g t r e a t m e n t . Means - 1 s t a n d a r d e r r o r . REST N=10 •= ACTIVE FISH A = RECOVERY FISH -1st HOUR I I O 15 30 4 5 6 0 4-fc RECOVERY N=10 60 75 9 0 TIME(MINUTES) 105 120 q u i c k l y r e v e r s e d d u r i n g r e c o v e r y . E v e n t h e s h o r t i n t e r v a l s o f r e s t a t e a c h b l o o d s a m p l i n g t i m e p r o d u c e d m a r k e d r e d u c t i o n s i n b o t h c o m p o n e n t s . I n c r e a s e s i n v e n t i l a t i o n a r e commonly a s s o c i a t e d w i t h e x e r c i s e i n t e l e o s t s ( S a u n d e r s , 1 9 6 2 ; S t e v e n s a n d R a n d a l l , 1 9 6 7 a, b; D a v i s , 1 9 6 8 ) and may be e f f e c t e d b y e i t h e r a m e c h a n i s m s i m i l a r t o t h e H a r r i s o n j o i n t - t e n d o n r e f l e x o f mammals ( S t e v e n s and R a n d a l l , 1 9 6 7 a) o r a d i r e c t s t i m u l a t o r y a c t i o n o f c i r c u l a t o r y c a t e c h o l a m i n e s on c e n t r a l r e s p i r a t o r y c e n t r e s ( W a i t z e n e g g e r , 1 9 6 7 ) . The r a t e i n c r e a s e s r e p o r t e d h e r e ( 1 0 % ) a r e l o w e r t h a n t h o s e ( 30%) o b s e r v e d b y S t e v e n s a n d R a n d a l l (1967 a ) , b u t i n s p e c t i o n o f r e c o r d i n g s t a k e n d u r i n g a c t u a l c h a s i n g i n d i c a t e t h a t t h e i m m e d i a t e l y p o s t - e x e r c i s e v a l u e s r e p o r t e d a r e s i g n i -f i c a n t u n d e r e s t i m a t i o n s o f mean v e n t i l a t o r y f r e q u e n c i e s a t t a i n e d b y t h e e x e r c i s e d t r e a t m e n t g r o u p . E l e v a t i o n s o f b u c c a l p r e s s u r e , h o w e v e r , a r e s i m i l a r t o t h o s e m e a s u r e d a t m o d e r a t e t o f a t i g u e swimming s p e e d s i n s a l m o n ( D a v i s , 1 9 6 8 ) . E x t r a p o l a t i o n f r o m t h e d a t a p r e s e n t e d i n a r e c e n t s t u d y o f v e n t i l a t i o n i n t h e r a i n b o w t r o u t (Hughes and S a u n d e r s , 1 9 7 0 ) s u g g e s t s t h a t c h a s e d f i s h e l e v a t e d t h e i r b r e a t h i n g v o l u m e s 2.5 - 3.0 f o l d i n t h e p r e s e n t s t u d y . A 4 f o l d i n c r e m e n t i n v e n t i l a t o r y f l o w v-7as c a l c u l a t e d f o r m o d e r a t e l y swimming t r o u t b y S t e v e n s a n d R a n d a l l (1967 a, b ) . However, i t i s l i k e l y t h a t v e n t i l a t i o n v o l u m e w o u l d be e n h a n c e d b y "ram" v e n t i l a t i o n ( M u i r and K e n d a l l , 1 9 6 8 ) d u r i n g t h e mouth o p e n i n g p h a s e o f t h e b r e a t h i n g c y c l e when swimming a g a i n s t a c o n s t a n t c u r r e n t i n a w a t e r t u n n e l . The d a t a r e p o r t e d a b o v e a d d * n o t h i n g new t o o u r know-l e d g e o f t e l e o s t p h y s i o l o g y b y t h e m s e l v e s , b u t do d e m o n s t r a t e 54 t h a t t h e d e s i r e d e f f e c t s were p r o d u c e d . W i t h t h e e x c e p t i o n o f a s l i g h t f a l l i n d o r s a l a o r t i c p r e s s u r e a t t r i b u t a b l e t o s e r i a l b l o o d s a m p l i n g , t h e r e s t i n g t r e a t m e n t g r o u p r e m a i n e d i n t h e " r o u t i n e " c o n d i t i o n t h r o u g h o u t t h e e x p e r i m e n t a l p e r i o d . T h e v e n t i l a t o r y and c a r d i o v a s c u l a r c o r r e l a t e s o f c h a s i n g were v e r y s i m i l a r t o t h o s e p r e v i o u s l y d o c u m e n t e d i n r a i n b o w t r o u t d u r i n g c o n t r o l l e d swimming a t m o d e r a t e s p e e d s ( S t e v e n s and R a n d a l l , 1 9 6 7 a, b ) . The l a t t e r w o r k e r s m e a s u r e d a 5 f o l d r i s e i n m e t a b o l i c r a t e a t t h i s e x e r c i s e l e v e l ; i t d o e s n o t seem u n r e a s o n a b l e t o e s t i m a t e a s i m i l a r i n c r e a s e i n o x y g e n consump-t i o n i n t h e c h a s e d a n i m a l s . R e c o v e r y was c h a r a c t e r i z e d b y a r e t u r n t o r e s t i n g l e v e l s i n t h e p a r a m e t e r s m e a s u r e d . B. The E f f e c t o f E x e r c i s e on B r a n c h i a l Sodium F l u x e s B e f o r e p r e s e n t a t i o n a n d e v a l u a t i o n o f t h e s e r e s u l t s , u s e o f t h e t e r m " b r a n c h i a l " i n r e f e r e n c e t o t h e m e a s u r e d f l u x e s n e e d s j u s t i f i c a t i o n , f o r i o n s may move b e t w e e n i n t e r n a l and e x t e r n a l m e d i a a c r o s s f o u r m a i n r e g i o n s o f a t e l e o s t : t h e g i l l , e p i t h e l i u m , t h e u r i n a r y s y s t e m , t h e i n t e s t i n a l s y s t e m , and t h e s k i n o f t h e g e n e r a l b o d y s u r f a c e . I n t h e s e e x p e r i m e n t s , u r i n a r y r e l e a s e o f e l e c t r o l y t e s was p r e v e n t e d by c a t h e t e r i z a t i o n . I n t e s t i n a l a b s o r p t i o n o f s o d i u m was n e g a t e d by t h e f a c t t h a t r a i n b o v ; t r o u t do n o t d r i n k i n f r e s h x^7ater ( S h e h a d e h and Gordon,19695. P r e - e x p e r i m e n t a l s t a r v a t i o n e l i m i n a t e d f a e c a l c o n t a m i n a t i o n o f t h e e x t e r n a l medium, b u t d u r i n g some t r i a l s , a g e l a t i n o u s t u b e o f m u c o i d m a t e r i a l was v e n t e d f r o m t h e a n u s . Howaver S h e h a d e h and G o r d o n (1969) h a v e d e m o n s t r a t e d t h a t t h i s m a t e r i a l , w h i c h n o r m a l l y e n c l o s e s f a e c e s i n f e d f i s h , i s d e v o i d o f s o d i u m . The i m p e r m e a b i l i t y o f Salmo g a i r d n e r i s k i n t o 55 s o d i u m h a s b e e n p r o v e n r e p e a t e d l y (Holmes.,1959; Fromm,1968). Th e a s s u m p t i o n o f an e x c l u s i v e l y b r a n c h i a l o r i g i n f o r t h e o b s e r v e d f l u x e s w o u l d , t h e r e f o r e , seem s o u n d . The p h y s i c a l d i m e n s i o n s o f t r o u t i n e a c h e x p e r i m e n t a l g r o u p a r e t a b u l a t e d i n T a b l e I I ; t h e mean s i z e o f r e s t i n g f i s h was o b v i o u s l y s l i g h t l y l a r g e r t h a n t h a t o f t h e o t h e r two s e t s . However c o e f f i c i e n t s o f c o n d i t i o n f o r t h e g r o u p s d i d n o t d i f f e r s i g n i f i c a n t l y , i n d i c a t i n g a common b o d y w e i g h t t o g i l l s u r f a c e a r e a r e l a t i o n s h i p f o r t h e n a r r o w w e i g h t r a n g e u s e d , a n d t h e r e -f o r e p e r m i t t i n g c o m p a r i s o n o f f l u x r a t e s b e t w e e n g r o u p s on a p e r 100 g b a s i s . D a t a h a s b e e n e x p r e s s e d i n ug/100 g / m i n u t e f o r c o n v e n i e n c e i n d i s c u s s i n g t h e movements o f v e r y s m a l l amounts o f s o d i u m o v e r s h o r t t i m e i n t e r v a l s . B r a n c h i a l s o d i u m f l u x r a t e s a r e p r e s e n t e d f o r t h e r e s t i n g , a c t i v e , and r e c o v e r y t r e a t m e n t g r o u p s i n F i g . 9 a n d a r e s u m m a r i z e d i n T a b l e I I I . A v e r a g e e x t e r n a l s o d i u m c o n c e n -t r a t i o n ( T a b l e I I I ) d i d n o t d i f f e r s i g n i f i c a n t l y among t h e t h r e e e x p e r i m e n t a l g r o u p s a n d t h u s was n o t a f a c t o r c a u s i n g t h e o b s e r v e d d i f f e r e n c e s i n f l u x r a t e s . R e s t i n g a n i m a l s m a i n t a i n e d a s t a t e o f s o d i u m e q u i l i b r i u m a t t h e g i l l s , i n f l u x (17.62 ug/100 g / m i n u t e ) a n d e f f l u x (16.88 ug/100 g / m i n u t e ) b e i n g a p p r o x i m a t e l y e q u a l s o t h a t t h e r e was o n l y a v e r y s l i g h t mean n e t u p t a k e o f t h e i o n . D u r i n g a c t i v i t y , h o w e v e r , b r a n c h i a l e f f l u x i n c r e a s e d m a r k e d l y ( 7 0 % , p < 0.01) w h i l e i n f l u x r e m a i n e d i d e n t i c a l t o r e s t i n g l e v e l s . C o n s e q u e n t l y , t h e r e was an e x t r e m e l y s i g n i f i c a n t (p < .001) n e t l o s s o f s o d i u m a c r o s s t h e g i l l s . O v e r t h e r e c o v e r y p e r i o d , a f t e r an h o u r o f e x e r c i s e , t h e f i s h r e t u r n e d t o a s t a t e o f p o s i t i v e b a l a n c e t h r o u g h a r e d u c t i o n (p < 0.001) i n t h e e f f l u x p a r a m e t e r t o 56 Table I I . Physical dimensions of trout i n the three experimental groups of Section I. Means - standard e r r o r . Resting Active Recovery N = 10 N = 11 N = 11 Body weight (g) 259.66 ± 12.79 233.95 - 11.19 228.17 - 8.05 P 1 = n.s. p^< .05 P 2 = n.s. Length (cm) 29.95 ± 0.50 29.65 - 0.49 28.81 - 0.45 P 1 s= n.s. = n.s. p2 = n.s. Fork length 28.63 - 0.47 28.01 - 0.51 27.62 - 0.40 (cm) (cm) o f condition P 1 = n.s. p 1 = n.s, P 2 = n.s, Max.depth 6.18 - 0.14 5.91 ± 0.14 5.87 t 0.09 P 1 = n.s. p x = n.s, P 2 = n.s. C o e f f i c i e n t 1.101 - 0.022 1.062 - 0.028 1.084 i 0.029 p ^ j ^ n . s . p 1 = n.s, v;eight x 100-(fork length) &2 = n*S' p 1 = s i g n i f i c a n c e with respect to corresponding r e s t i n g value. P 2 = s i g n i f i c a n c e with respect to corresponding a c t i v e value. 57 F i g u r e 9 B r a n c h i a l sodium f l u x r a t e s over c o n s e c u t i v e i n t e r -v a l s o f the e x p e r i m e n t a l p e r i o d s i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . B l a c k b a r s = mean b r a n c h i a l sodium i n f l u x r a t e s ; d o t t e d b a r s «= mean b r a n c h i a l sodium e f f l u x r a t e s ; c l e a r b a r s = mean b r a n c h i a l sodium n et f l u x r a t e s . The v e r t i c a l l i n e s r e p r e s e n t 1 s t a n d a r d e r r o r o f each mean. S t a t i s t i c a l Comparisons: (Numbers r e f e r t o means o f i n t e r v a l s as l a b e l l e d a t the head o f the graph.) R e s t i n g : I n f l u x Rate. F = 1.20, n.s. 4 5 2 3 1 E f f l u x Rate. F = 0 . 5 3 , n . s . 3 5 4 2 1 Net F l u x Rate. F = 0.34, n.s. 4 2 5 1 3 A c t i v e : I n f l u x Rate. F = 1.37, n.s. 4 3 2 5 1 E f f l u x Rate. F = 0.48, n.s. 2 3 1 5 4 Net F l u x Rate. F = 1.25, n.s. 1 2 3 5 4 Recovery: I n f l u x Rate. F = 2.44, n.s. 3 5 4 2 1 E f f l u x Rate. F = 1.48, n.s. 3 4 5 2 1 Net F l u x Rate. F = 0.80, n.s, 3 5 4 1 2 A = s i g n i f i c a n t l y d i f f e r e n t from c o r r e s p o n d i n g r e s t i n g v a l u e (p < .05) B = s i g n i f i c a n t l y d i f f e r e n t from c o r r e s p o n d i n g a c t i v e v a l u e (p < .05) — = not s i g n i f i c a n t l y d i f f e r e n t from o t h e r c o r r e s -p onding v a l u e s (p "7 .05) T I M E PERIOD O F DETERMINATION ( M I N U T E S ) 1 2 3 4 5 0-5 average RCCT IMP 5-15 15-30 30-45 45-60 0-60 ACTIVE FISH 60-65 65-75 75-90 90-105 105-120 60-120 : P p ^ V E R Y <D C C D o o U J X z> Q O to I < X u z •30 : I +20 +10 - -, 0 » • -10 mm V 3 C -20 : • i.t -30 1 n=10 -30 : 5 -10-+30 +20 + 0 -10 -20 h -30 : I n=10 •5 n=10 r n=ll I _ _ B n=10 n=K) »7 X n=11 A A n=ll B B I n=ll 1 S n=ll _ B B n=9 n=9 J n=ll _ B B n=10 n=ll Pi _ A A n=ll _ B B RESTING ACTIVE RECOVERY 58 Table I I I . Average b r a n c h i a l sodium f l u x rates over the experimental periods. Means - 1 standard e r r o r . Resting Active Recovery External Sodium N = 10 N = 11 N = 11 centrat (ug/ml) Con ion 1.550 - 0.151 1.612 - 0.151 1.851 - 0.254 = n.s. p 1 = n . s . P 2 = n.s. Sodium Influx N = 10 N = 11 N = 11 Rate (ug/100 g/min) + 17.62 - 1.15 + 16.41 - 1.49 + 19.24 ± 2.86 P 1 = n . s . p = n.s, P 2 = n.s, Sodium E f f l u x N = 10 N = 11 N = 11 Rate (ug/100 g/min) - 16.88 - 1.57 - 28.50 ± 3.55 - 14.70 ± 2.36 p 1 < .01 p^ = n.s. P 2 < .001 Sodium Net N = 10 N = 11 N = 11 Flux Rate (ug/100 g/min) + 0.74 - 1.43 - 12.14 - 2.94 +4.54 - 1.99 P 1 <.01 p^ = n.s, P 2 < .001 p^ = s i g n i f i c a n c e with respect to corresponding r e s t i n g value, ^2 = s i g n i f i c a n c e with respect to corresponding a c t i v e value r e s t i n g v a l u e s , a g a i n w i t h o u t s i g n i f i c a n t c h a n g e o f t h e i n f l u x p a r a m e t e r . I t w o u l d a p p e a r , t h e r e f o r e , t h a t b r a n c h i a l s o d i u m i n f l u x i s i n s e n s i t i v e , b u t e f f l u x e x t r e m e l y l a b i l e , t o some f a c t o r o r f a c t o r s a s s o c i a t e d w i t h e x e r c i s e . The p r e s e n t r e s u l t s c l a r i f y t h e o b s e r v a t i o n s o f R a n d a l l e t aJL.(1969) who 22 n o t e d t h a t a c t i v i t y a u g m e n t e d t h e r e l e a s e o f i n j e c t e d Na f r o m t h e g i l l s o f f r e s h w a t e r a d a p t e d t r o u t b u t were u n a b l e t o d e c i d e w h e t h e r t h e e f f e c t r e p r e s e n t e d a s t i m u l a t i o n o f s o d i u m t u r n o v e r r a t e o r o f t h e e f f l u x component a l o n e . D a t a p r e s e n t e d h e r e i n d i c a t e s t h e l a t t e r t o be t r u e . I n e a c h t r e a t m e n t g r o u p , f l u x e s were m e a s u r e d o v e r t h e f i r s t 5, t h e n e x t 10, a n d t h e f o l l o w i n g t h r e e 15 m i n u t e t i m e p e r i o d s o f t h e e x p e r i m e n t a l h o u r ( F i g . 9 ) . The e r r o r i n e s t i m a t i n g e x c h a n g e r a t e s o v e r t h e i n i t i a l 5 m i n u t e i n t e r v a l was h i g h a n d i s m a n i f e s t e d by t h e l a r g e s t a n d a r d e r r o r s on a l l t h r e e f l u x c o m p o n e n t s f o r t h i s p e r i o d i n e a c h s e t o f f i s h . T h i s i n a c c u r a c y c a n be t r a c e d t o a number o f c a u s e s : t h e c h a n g e i n t o t a l s o d i u m an d r a d i o s o d i u m c o n c e n t r a t i o n o f t h e w a t e r were m i n i m a l a n d s u b j e c t t o l i m i t a t i o n s o f a n a l y t i c a l p r e c i s i o n ; t h e m e a s u r e m e n t s assumed i n s t a n t a n e o u s a n d c o m p l e t e m i x i n g o f t h e l a b e l l e d s o l u t i o n w i t h t h e o r i g i n a l l y u n l a b e l l e d e x t e r n a l medium, w h i c h was p r o b a b l y u n t r u e ; most i m p o r t a n t l y , t h e r e 22 c o u l d h a v e o c c u r r e d a s l i g h t e x c h a n g e o f Na i o n s v ; i t h t h e 2 3 s m a l l number o f Na i o n s a d s o r b e d t o t h e mucus o f t h e a n i m a l ' s e p i t h e l i u m (Fromm,1968). T h i s l a t t e r f a c t o r w o u l d o n l y h a v e b e e n e f f e c t i v e u n t i l t h e s p e c i f i c a c t i v i t y o f a d s o r b e d s k i n s o d i u m e q u i l i b r a t e d w i t h t h a t o f f r e e s o d i u m i n t h e w a t e r , b u t o v e r t h i s s h o r t i n t e r v a l w o u l d h a v e b e e n d e t e c t e d as an i n f l u x due t o t h e d i s a p p e a r a n c e o f r a d i o t r a c e r f r o m t h e e x t e r n a l 60 c o m p a r t m e n t . As e f f l u x was n o t d i r e c t l y m e a s u r e d , b u t com-p u t e d as t h e d i f f e r e n c e b e t w e e n i n f l u x a n d n e t f l u x , a r t i f i c i a l e n h a n c e m e n t o f i n f l u x w o u l d h a v e a u t o m a t i c a l l y e l e v a t e d t h i s c o m p o n e n t . T h e r e was i n f a c t a t e n d e n c y f o r h i g h e r u n i -d i r e c t i o n a l f l u x e s d u r i n g t h e f i r s t 5 m i n u t e s t h a n d u r i n g s u b -s e q u e n t p e r i o d s f o r a l l t h r e e g r o u p s , b u t t h e s e e l e v a t i o n s w e r e n o t s t a t i s t i c a l l y s i g n i f i c a n t i n t h e r e s t i n g and a c t i v e t r o u t . I n t h e r e c o v e r y g r o u p , t h e i n i t i a l h i g h i n f l u x a t t a i n e d b o r d e r l i n e s i g n i f i c a n c e ( D u n c a n ' s T e s t , 5% p r o t e c t i o n l e v e l , a l t h o u g h n o t r e f l e c t e d i n w i t h r e s p e c t t o v a l u e s f o r t h e f i n a l t h r e e i n t e r v a l s o f m e a s u r e m e n t . However, i n l i g h t o f t h e a b o v e d i s c u s s i o n , no b i o l o g i c a l i m p o r t a n c e i s a t t a c h e d t o t h i s d i f f e r e n c e . F i g u r e 9, a n d t h e a c c o m p a n y i n g s i g n i f i c a n c e t e s t s , t h e r e f o r e i n d i c a t e t h a t , w i t h i n t h e d e t e c t i o n l i m i t s o f t h e m e t h o d s u s e d , t h e r e o c c u r r e d no v a r i a t i o n o f i n f l u x , e f f l u x , a n d n e t f l u x c o m p o n e n t s o f g i l l s o d i u m e x c h a n g e w i t h i n e a c h t r e a t m e n t g r o u p o v e r t h e e x p e r i m e n t a l h o u r . T h i s i n t u r n i m p l i e s t h a t t h e l a g p h a s e s i n t h e c h a n g e o v e r f r o m a b r a n c h i a l f l u x r a t e p a t t e r n d i s t i n c t i v e o f r e s t t o t h a t c h a r a c t e r i s t i c o f a c t i v i t y , o r f r o m t h e l a t t e r t o t h e t y p i c a l r e c o v e r y a r r a n g e -ment, were e x t r e m e l y s h o r t . An e x a m i n a t i o n o f n e t f l u x r a t e s i n t h e r e c o v e r y g r o u p ( F i g . 10) i s ' e s p e c i a l l y p e r s u a s i v e o f t h e p o i n t , f o r m e a s u r e -m e nts o f t h i s p a r a m e t e r w e r e b a s e d s o l e l y on f l a m e p h o t o m e t r i c a n a l y s e s w h i c h , d u r i n g t h e f i r s t 5 m i n u t e p e r i o d , were f a r more a c c u r a t e t h a n i s o t o p e u p t a k e d e t e r m i n a t i o n s ( a n d t h e r e f o r e , u n i d i r e c t i o n a l f l u x e s ) . T h f s e d a t a d e m o n s t r a t e * t h a t t h e s w i t c h f r o m a n e g a t i v e t o a p o s i t i v e s o d i u m b a l a n c e w i t h t h e o n s e t o f 61 F i g u r e 10 B r a n c h i a l sodium n et f l u x r a t e s over c o n s e c u t i v e i n t e r v a l s o f the e x p e r i m e n t a l p e r i o d f o r the r e c o v e r y t r e a t m e n t group. The v e r t i c a l l i n e s r e p r e s e n t 1 s t a n d a r d e r r o r o f each mean. C h a s i n g ceased a t 60 minutes. S t a t i s t i c a l Comparisons: (Numbers r e f e r t o means o f i n t e r v a l s as l a b e l l e d a t the head o f the graph.) F = 4.68, p < .005 1 3 5 2 4 8 10 9 6 7 BRANCHIAL NET SODIUM FLUXES (jjg/lOOg/min.) O ^ h O O c o O - ^ N J o b b b b b b b T rO -U- O CO o b b b b T T T T" T T -r O Cn i _ rO Cn Cn CO o CO 73 -m-O O < m _3_ co O i 4x Cn Cn i Cn CO O O i O Cn O Cn i Cn ¥ o Cn O 00 r e c o v e r y o c c u r r e d a l m o s t i n s t a n t a n e o u s l y . The n e t f l u x e s o f t h e r e c o v e r y t r o u t c h a n g e d s i g n i f i c a n t l y b e t w e e n t h e l a s t 15 m i n u t e p e r i o d o f c h a s i n g and t h e f i r s t 5 m i n u t e s o f r e c o v e r y . F i g u r e 10 a l s o c o n f i r m s t h a t r e c o v e r y f i s h , d u r i n g t h e i r i n i t i a l h o u r o f e x e r c i s e , s u f f e r e d a n e t b r a n c h i a l s o d i u m d e f i c i t s i m i l a r t o t h a t o f t h e a c t i v e g r o u p ( F i g . 9 ) . T h e s e e x t r e m e l y r a p i d e f f e c t s , w h i c h a p p a r e n t l y i m p l i c a t e d o n l y b r a n c h i a l s o d i u m e f f l u x , were p r o b a b l y a s s o c -i a t e d w i t h a r e a d j u s t m e n t o f t h e r e s p i r a t o r y / o s m o r e g u l a t o r y c o m p r o m i s e a t t h e g i l l s . R e f e r e n c e t o F i g s . 5 - 8 and T a b l e I i n d i c a t e s t h a t t h e v e n t i l a t o r y a n d c a r d i o v a s c u l a r c o r r e l a t e s o f t h e s e c h a n g e s h a d o c c u r r e d b y 5 m i n u t e s a f t e r t h e i n c e p t i o n o f e x e r c i s e o r r e c o v e r y . As o u t l i n e d e a r l i e r ( p p . 8 - 1 0 ) an o s m o t i c d e f i c i t s h o u l d be c o n c o m i t a n t w i t h e l e v a t i o n o f g a s e x c h a n g e b e c a u s e o f i n c r e a s e d b l o o d p e r f u s i o n o f t h e h i g h s u r f a c e a r e a , t h i n w a l l e d r e s p i r a t o r y l a m e l l a e . A p r i n c i p a l mani-f e s t a t i o n o f s u c h a d e f i c i t w o u l d be an i n c r e a s e d s i m p l e d i f f u s i o n o f s o d i u m , t h e m a j o r p l a s m a c a t i o n , f r o m i n t e r n a l t o e x t e r n a l m i l i e u x . The 10% r i s e i n b r a n c h i a l s o d i u m e f f l u x f r o m 16.88 t o 28.50 ug/100 g / m i n u t e d u r i n g e x e r c i s e i s i n t e r -p r e t e d i n t h e s e t e r m s . T h e r e e x i s t , as y e t , no m e a s u r e m e n t s o f t h e d i f f u s i o n c o e f f i c i e n t f o r s o d i u m i n t e l e o s t g i l l t i s s u e so i t h a s n o t b e e n p o s s i b l e t o d e t e r m i n e w h e t h e r t h e o b s e r v e d i n c r e a s e i n s o d i u m e f f l u x was a t t r i b u t a b l e t o s i m p l e d i f f u s i o n on a t h e o r e t i c a l b a s i s . However, a v e r y t e n t a t i v e c a l c u l a t i o n , b a s e d on a number o f u n p r o v e n s u p p o s i t i o n s , was u n d e r t a k e n t o s e e i f t h i s e x p l a n a t i o n o f t h e e n h a n c e d e f f l u x was i n any way r e a s o n a b l e . T h e s e s u p p o s i t i o n s i n c l u d e d t h a t o f a b r a n c h i a l s o d i u m d i f f u s i o n c o e f f i c i e n t i d e n t i c a l t o t h a t o f mammalian c a p i l l a r i e s ( P a p p e n h e i m e r , 1 9 5 3 ) b e c a u s e o f t h e m a r k e d s i m i l a r -i t i e s b e t w e e n l a m e l l a r a n d c a p i l l a r y s t r u c t u r e ( N e w s t e a d , 1 9 6 7 ) . O t h e r p & s s u m p t i o n s c o m p r i s e d t h e u s e o f t h e l a m e l l a r a r e a o f Hughes (1966) f o r Salmo t r u t t a , t h e d i f f u s i o n d i s t a n c e o f N e w s t e a d (1967) f o r O n c h o r h y n c h u s k i s u t c h , a n d t h e t r a n s -e p i t h e l i a l p o t e n t i a l o f K e r s t e t t e r et. a_l . (1970) f o r a n a e s t h -e t i z e d r a i n b o w t r o u t a t c o m p a r a b l e e x t e r n a l s o d i u m c o n c e n t r a t i o n s . T h i s c o m p u t a t i o n y i e l d e d a maximum d i f f u s i o n a l e f f l u x o f a p p r o x i m a t e l y 3 ug/100 g / m i n u t e ; K e r s t e t t e r e t _ a l . ( 1 9 7 0 ) , b y m e t h o d s u n s t a t e d , e s t i m a t e d a v e r y s i m i l a r d i f f u s i o n a l l o s s (2 ug/100 g / m i n u t e ) . A c t i v e t r o u t i n t h e p r e s e n t s t u d y i n c r e a s e d b r a n c h i a l e f f l u x b y 12 ug/100 g / m i n u t e . I n l i g h t o f t h e u n c e r t a i n t i e s i n t h e a s s u m p t i o n s t a k e n , a g r e e m e n t b e t w e e n c a l c u l a t e d a n d o b s e r v e d v a l u e s w i t h i n an o r d e r o f m a g n i t u d e was e n c o u r a g i n g . R e s t i n g a n i m a l s m a i n t a i n e d o n l y a n e g l i g i b l e n e t b r a n c h i a l u p t a k e o f s o d i u m (0.74 ug/100 g / m i n u t e ) y e t p r e s u m a b l y s u f f e r e d g r e a t e r r e n a l l o s s ( S e c t i o n I I I ) ; on a w h o l e b o d y b a s i s , t h e t r o u t w e r e i n n e g a t i v e s o d i u m b a l a n c e , a s i t u a t i o n w h i c h o b v i o u s l y c o u l d n o t be i n d e f i n i t e l y e n d u r e d . T h i s c o n d i t i o n h a s b e e n e n c o u n t e r e d i n many o t h e r s t u d i e s ( e . g . M a e t z , 1 9 5 6 ; M a e t z et, aJL.,1964 a; L a h l o u a n d Sawyer, 1969) a n d h a s g e n e r a l l y b e e n a t t r i b u t e d t o s h o c k , s t r e s s , o r h a n d l i n g e f f e c t s w i t h o u t f u r t h e r e x p l a n a t i o n . I t i s p r o b a b l e t h a t i n c r e a s e s i n r e s p i r a t o r y e x c h a n g e w e r e a s s o c i a t e d w i t h r e c o v e r y f r o m a n a e s t h e t i z a t i o n and c a n n u l a t i o n ( s e e S e c t i o n I I I , F i g . 25) a n d c a u s e d d i s t u r b a n c e o f t h e b r a n c h i a l r e s p i r a t o r y / o s m o r e g u l a t o r y a d j u s t m e n t w i t h c o n c o m i t a n t i n c r e a s e s i n d i f f u s i o n a l s o d i u m 64 e f f l u x . H o u s t o n e_t a l . , (1969) h a v e d e t e c t e d v e r y m a r k e d d i s t u r b a n c e s i n w a t e r a n d e l e c t r o l y t e c o n c e n t r a t i o n s i n p l a s m a an d t i s s u e o f t h e b r o o k t r o u t , S a l v e l i n u s f o n t i n a l i s , f o r up t o 72 h o u r s a f t e r MS 222 a n a e s t h e s i a and v a s c u l a r c a t h e t e r -i z a t i o n , t h e same p r o c e d u r e s t o w h i c h r a i n b o w s i n t h e p r e s e n t s t u d y h a d b e e n s u b j e c t e d 10 - 48 h o u r s " p r i o r t o e x p e r i m e n t a t i o n . F o r i n d i v i d u a l r e s t i n g f i s h , n e t f l u x r a t e b o r e no r e l a t i o n s h i p t o i n f l u x r a t e b u t was p o s i t i v e l y c o r r e l a t e d ( r = 0.713, p < .05) w i t h e f f l u x r a t e , i n d i c a t i n g t h a t t h e s t a t e o f b a l a n c e f o r a p a r t i c u l a r t r o u t was d e t e r m i n e d l a r g e l y b y t h e m a g n i t u d e o f e f f l u x . T h i s c o r r e l a t i o n was a c c e n t u a t e d d u r i n g e x e r c i s e ( r = 0.915, p <z . 0 1 ) . D e s p i t e t h e f a c t t h a t r e s t i n g a n i m a l s w ere n o t i n a t r u l y " n o r m a l " s t a t e , d i f f e r e n c e s d e m o n s t r a t e d b e t w e e n g r o u p s o f s i m i l a r l y c a n n u l a t e d t r o u t s h o u l d s t i l l r e p r e s e n t e f f e c t s i n d e p e n d e n t o f t h o s e c a u s e d b y t h e common p r e - e x p e r i m e n t a l t r e a t m e n t . A r g u m e n t s h a v e b e e n p r e s e n t e d p r e v i o u s l y t h a t t h e mob-i l i z a t i o n o f c a t e c h o l a m i n e s d u r i n g e x e r c i s e i s r e s p o n s i b l e f o r b o t h t h e b r a n c h i a l v a s o d i l a t i o n i n c r e a s i n g t h e e f f e c t i v e p erme-a b i l i t y o f t h e r e s p i r a t o r y e x c h a n g e r a n d f o r t h e e l e v a t i o n o f c a r d i a c o u t p u t . T h e r e f o r e i t i s o f i n t e r e s t t o a s k w h e t h e r t h e t r u e c o u r s e o f v a r i a t i o n i n p l a s m a l e v e l s o f t h e s e s u b -s t a n c e s c a n be c o r r e l a t e d w i t h t h e a l m o s t i n s t a n t a n e o u s c h a n g e s i n b r a n c h i a l s o d i u m e f f l u x a n d h e a r t f u n c t i o n . The work o f Nakano and T o m l i n s o n (1967) on r a i n b o w t r o u t d e m o n s t r a t e d a r a p i d i n c r e a s e ( l e s s t h a n 10 m i n u t e s ) i n p l a s m a l e v e l s a t t h e o n s e t o f e x e r c i s e , b u t t h i s e l e v a t i o n was m a i n t a i n e d f o r a t l e a s t 3 h o u r s i n t o r e c o v e r y . S o d i u m e f f l u x ( F i g . 9 ) , h e a r t r a t e ( F i g . 5 ) , a n d c a r d i a c o u t p u t ( S t e v e n s a n d R a n d a l l , 1 9 6 7 b) d r o p r a p i d l y a f t e r t e r m i n a t i o n o f swimming. T h u s c a t e c h o l a -m i n e s may w e l l be i n v o l v e d i n t h e i n i t i a l b r a n c h i a l a n d c a r d i a c a d a p t a t i o n t o t h e r e s p i r a t o r y demands o f a c t i v i t y , b u t o t h e r f a c t o r s may o v e r - r i d e t h e s e a d r e n e r g i c e f f e c t s as s o o n as t h e y a r e no l o n g e r r e q u i r e d . The p e r s i s t e n c e o f h i g h c i r c u l a t o r y c o n c e n t r a t i o n s o f a d r e n a l i n e and n o r a d r e n a l i n e a f t e r e x e r c i s e may r e f l e c t a l o w a c t i v i t y o f b r e a k d o w n m e c h a n i s m s i n t e l e o s t t i s s u e . One c o u l d a l s o a r g u e t h a t c a t e c h o l a m i n e s e x e r t o n l y p a r t i a l c o n t r o l o v e r c a r d i a c a c t i v i t y a n d b r a n c h i a l p e r m e a b i l i t y a n d a c t a s p o t e n t i a t o r s f o r t h e o b s e r v e d e f f e c t s . T h u s an i n c r e a s e d c a r d i a c o u t p u t c o u l d be c a u s e d b y g r e a t e r v e n o u s r e t u r n a t t h e o n s e t o f a c t i v i t y . , b u t f a c i l i t a t e d b y t h e a c t i o n o f a d r e n a l i n e on t h e m y o c a r d i u m t o f a v o u r a b l y c h a n g e t h e r e l a t i o n s h i p b e t w e e n s t r o k e v o l u m e an d f i l l i n g p r e s s u r e ( B e n n i o n , 1 9 6 8 ) . A t t h e same t i m e , c a t e c h o l a m i n e s w o u l d s t i m -u l a t e t h e d i l a t i o n o f r e s p i r a t o r y s h u n t s a t t h e g i l l s , b u t t h e f i l l i n g o f a p a r t i c u l a r l a m e l l a w o u l d s t i l l be d e p e n d e n t u p o n a s p e c i f i c o p e n i n g p r e s s u r e . A t r e c o v e r y , v e n o u s r e t u r n , c a r d i a c o u t p u t , a n d v e n t r a l a o r t i c p r e s s u r e w o u l d t e n d t o f a l l i n c a u s a t i v e s e q u e n c e , an d t h u s t h e number o f r e s p i r a t o r y l a m e l l a e p e r f u s e d ( i . e . b r a n c h i a l p e r m e a b i l i t y ) w o u l d be r e d u c e d d e s p i t e t h e c o n t i n u a n c e o f h i g h c a t e c h o l a m i n e l e v e l s i n p l a s m a . C l e a r l y f u r t h e r r e s e a r c h on t h e n a t u r e o f a c t i o n o f c a t e c h o l a m i n e s a n d t h e i n t e g r a t i o n o f c a r d i o v a s c u l a r a d j u s t -ment t o e x e r c i s e i n t e l e o s t s i s n e c e s s a r y . I o n e x c h a n g e m e c h a n i s m s o f t h e f i s h g i l l a r e p o o r l y u n d e r s t o o d a t p r e s e n t a n d t h e l i t t l e k n o w l e d g e a v a i l a b l e i s c o n f o u n d e d by o b v i o u s s p e c i e s d e p e n d e n t d i f f e r e n c e s ; e x c h a n g e d i f f u s i o n , a c t i v e t r a n s p o r t , a c t i v e c o u p l e d t r a n s p o r t , b a c k -t r a n s p o r t , d r i n k i n g , a n d s i m p l e d i f f u s i o n h a v e a l l b e e n i m p l i -c a t e d i n s o d i u m f l u x e s b e t w e e n i n t e r n a l a n d e x t e r n a l m i l i e u x i n d i f f e r e n t r a d i o t r a c e r s t u d i e s ( M a e t z , 1 9 5 6 ; H o u s e , 1 9 6 3 ; M a e t z a n d G a r c i a - R o m e u , 1 9 6 4 ; G a r c i a - R o m e u a n d M a e t z , 1 9 6 4 ; G a r c i a - R o m e u and M o t a i s , 1 9 6 6 ; M o t a i s e t a l . , 1 9 6 6 ; E v a n s , 1 9 6 7 ; M a e t z , 1 9 6 9 ; P o t t s e t a l , 1 9 7 0 ; M o r r i s a n d B u l l , 1 9 7 0 ; K e r s t e t t e r e t a l , 1 9 7 0 ) . T h e o n l y g e n e r a l c o n c l u s i o n p e r t i n e n t t o t h e p r e s e n t s t u d y w h i c h c a n be drawn f r o m t h e s e i n v e s t i g a t i o n s i s t h a t b r a n c h i a l s o d i u m i n f l u x i n f r e s h w a t e r o c c u r s b y an a c t i v e t r a n s p o r t m e c h a n i s m w h i c h may i n some way be l i n k e d t o t h e e x t r u s i o n o f a n o t h e r c a t i o n (NH*.: M a e t z a n d G a r c i a - R o m e u , 1 9 6 4 ; G a r c i a - R o m e u a n d M o t a i s , 1966; H + : K e r s t e t t e r e t a_l,19 70) and w h i c h i s i n d e p e n d -e n t o f c h l o r i d e t r a n s p o r t ( G a r c i a - R o m e u and M a e t z , 1 9 6 4 ) . E x c h a n g e d i f f u s i o n , i n t h e s e n s e o f M o t a i s e t aJL.(1966) ( a n " o r g a n i z e d l e a k i n e s s " i n w h i c h u n i d i r e c t i o n a l s o d i u m f l u x e s a r e l i n k e d on a one f o r one b a s i s b y a h y p o t h e t i c a l c a r r i e r ) i s c h a r a c t e r i s t i c o f some e u r y h a l i n e f o r m s b u t h a s n o t b e e n o b s e r v e d when t h e a n i m a l s were a d a p t e d t o f r e s h w a t e r ( M o t a i s e t a l . , 1 9 6 6 ; E v a n s , 1 9 6 7 ) . I n l i g h t o f t h i s p a u c i t y o f i n f o r m a t i o n , a n a l y s i s o f u n i d i r e c t i o n a l b r a n c h i a l s o d i u m f l u x r a t e s , w h i c h h a v e n o t p r e v i o u s l y b e e n m e a s u r e d i n i n t a c t Salmo g a i r d n e r i must p r o c e e d f r o m v e r y b a s i c c o n s i d e r a t i o n s . R e c e n t m e a s u r e m e n t s o f t r a n s -e p i t h e l i a l p o t e n t i a l s i n f r e s h w a t e r a d a p t e d r a i n b o w s ( K e r s t e t t e r e t _ al.,1970; R a n d a l l and C o n t e , p e r s o n a l c o m m u n i c a t i o n ) h a v e r e v e a l e d t h a t i n t e r n a l f l u i d s a r e s l i g h t l y p o s i t i v e w i t h r e s p e c t t o t h e e x t e r n a l medium. T h e r e f o r e t h e i n w a r d movement o f s o d i u m o c c u r s a g a i n s t b o t h an e l e c t r i c a l a n d a c h e m i c a l g r a d i e n t . A p p l i c a t i o n o f t h e U s s i n g e q u a t i o n ( U s s i n g , 1 9 4 9 a ) t o t h i s s i t u a t i o n ( [Na] i = 117.97 u E q / m l ; | N a j o = .067 u E q / m l ; T.E.P. = +6.0 mv.) s u g g e s t s t h a t t h e e f f l u x / i n f l u x r a t i o s h o u l d a p p r o x i m a t e 2244 i f o n l y p a s s i v e m e c h a n i s m s a r e i n v o l v e d . On t h e c o n t r a r y , t h e r a t i o f o r r e s t i n g t r o u t i s a l m o s t u n i t y , and n o t g r e a t l y d i f f e r e n t d u r i n g e x e r c i s e o r r e c o v e r y ; c l e a r l y t h e U s s i n g c r i t e r i o n f o r t h e c o n t r i b u t i o n o f a c t i v e t r a n s p o r t m e c h a n i s m s t o t h e i n w a r d f l u x o f s o d i u m i s s a t i s f i e d . R i c h a r d s an d Fromm (19 70) h a v e r e c e n t l y d e m o n s t r a t e d in_ v i t r o t h a t t h e s o d i u m u p t a k e o f t h e p e r f u s e d t r o u t g i l l i s an-A.T.P. d e p e n d e n t p r o c e s s . T h u s a t l e a s t p a r t o f t h e m e a s u r e d s o d i u m i n f l u x r a t e must be a t t r i b u t a b l e t o a c t i v e t r a n s p o r t ; t h e r e m a i n d e r , i f any, c o u l d c o n s i s t o f s i m p l e d i f f u s i o n ( n e g l i g i b l e ) and e x c h a n g e d i f f u s i o n . T h i s l a t t e r m e c h a n i s m i s e s s e n t i a l l y p a s s i v e and w o u l d s i m p l y e x c h a n g e i n t e r n a l and e x t e r n a l s o d i u m i o n s (no n e t t r a n s p o r t o f t h e e l e c t r o l y t e ) , b u t w o u l d be d e t e c t e d i n b o t h i n f l u x and e f f l u x p a r a m e t e r s by t h e r a d i o -t r a c e r t e c h n i q u e . As s u c h , i t w o u l d c o n t r i b u t e e q u a l l y t o t h e two u n i d i r e c t i o n a l f l u x e s . E x c h a n g e d i f f u s i o n c o u l d h y p o t h e t i c a l l y u t i l i z e e i t h e r t h e same c a r r i e r as a c t i v e t r a n s -p o r t o r a c o m p l e t e l y s e p a r a t e a g e n t ( M o t a i s et, a_l.,1966; M a e t z , 1 9 6 9 ) . A p r i o r i , an a c t i v e t r a n s p o r t c o n t r i b u t i o n t o e f f l u x seems most u n l i k e l y , and h a s n e v e r b e e n d e m o n s t r a t e d i n f r e s h w a t e r t e l e o s t s ; e f f l u x s h o u l d , t h e r e f o r e , c o n s i s t o f s i m p l e d i f f u s i o n a n d e x c h a n g e d i f f u s i o n i f p r e s e n t . The 70% r i s e i n e f f l u x d u r i n g e x e r c i s e was n o t a s s o c i a t e d w i t h any c h a n g e i n i n f l u x r a t e and t h u s w o u l d n o t seem t o i n v o l v e e x c h a n g e d i f f -u s i o n . C o n s e q u e n t l y t h e i n c r e m e n t i n e f f l u x p r o b a b l y c o n s i s t e d e n t i r e l y o f s i m p l e d i f f u s i o n . 68 E f f e c t i v e b r a n c h i a l p e r m e a b i l i t y t o e i t h e r i o n s o r g a s e s w i l l be d e t e r m i n e d by t h e f a c t o r AD ( a r e a x d i f f u s i o n X c o e f f i c i e n t / d i s t a n c e , p . 4 ) . As c o n c e n t r a t i o n g r a d i e n t s f o r b o t h o x y g e n ( S t e v e n s and R a n d a l l , 1 9 6 7 b) a n d s o d i u m w i l l r e m a i n e s s e n t i a l l y u n c h a n g e d d u r i n g e x e r c i s e , s i m p l e d i f f u s i o n f l u x e s may be t a k e n as r e p r e s e n t a t i v e o f e f f e c t i v e p e r m e a b i l i t i e s and v i c e v e r s a . C h a n g e s i n A and X s h o u l d h a v e t h e same e f f e c t on t h e d i f f u s i o n o f b o t h s o d i u m and o x y g e n . I f i t i s assumed t h a t D e i t h e r r e m a i n s s t a b l e o r c h a n g e s e q u a l l y f o r t h e two s t i b s t a n c e s d u r i n g a ugmented l a m e l l a r b l o o d f l o w , t h e n t h e f o l l o w i n g a r g u m e n t s may be a d v a n c e d . (1) A p a r t i c u l a r i n c r e a s e i n t h e s i m p l e d i f f u s i o n a l e f f l u x o f s o d i u m w i l l i m p l y a s i m i l a r r i s e i n t h e o x y g e n t r a n s f e r f a c t o r ( w h i c h i s d i r e c t l y p r o p o r t i o n a l t o o x y g e n up-t a k e as t h e g r a d i e n t i s i n v a r i a n t ) . T h u s i f a l l b r a n c h i a l s o d i u m e f f l u x o c c u r s b y s i m p l e d i f f u s i o n , t h e n a 70% r i s e d u r i n g e x e r c i s e s h o u l d be a s s o c i a t e d w i t h o n l y a 70% i n c r e a s e i n m e t a b o l i c r a t e . Y e t t h i s seems i m p o s s i b l e as t r o u t more t h a n d o u b l e t h e i r o x y g e n u p t a k e i n r e s p o n s e t o o n l y m i n o r d i s t u r b a n c e . V e n t i l a t o r y a n d c a r d i o v a s c u l a r d a t a p r e s e n t e d i n t h e f i r s t p a r t o f t h i s s e c t i o n was i n d i c a t i v e o f a 5 - f o l d r i s e ( S t e v e n s and R a n d a l l , 1 9 6 7 a, b) i n o x y g e n u p t a k e d u r i n g c h a s i n g . T h u s t h e 70% e l e v a t i o n o f e f f l u x must r e p r e s e n t an a p p r o x i m a t e l y 5 - f o l d i n c r e a s e i n t h e s i m p l e d i f f u s i o n component ( Y ) o f e f f l u x . T h i s s t a t e m e n t i n t u r n i m p l i e s t h e e x i s t e n c e o f an e x c h a n g e d i f f u s i o n component ( J 3 ) t o e f f l u x ; t h e f o l l o w -i n g s i m p l e c a l c u l a t i o n may be p e r f o r m e d : A t r e s t Y + £ = 17 ug/100 g/ m i n . D u r i n g a c t i v i t y 5 Y +^ = 29 ug/100 g/min. 69 Y = 3 ug/100 g/min. £ = 14 ug/100 g/min. This very elementary analysis would i n d i c a t e that, i f the above assumptions are correct, only a small portion of the e f f l u x at r e s t was caused by simple d i f f u s i o n , the majority being due to exchange d i f f u s i o n . Consequently i n f l u x would also be l a r g e l y exchange d i f f u s i o n (14 ug/100 g/min.) with only about 3 ug/100 g/ min. of active uptake. The fa c t that exchange d i f f u s i o n has not previously been demonstrated i n fresh water t e l e o s t s must weigh against t h i s hypothesis. (2) Again presuming an i n t e r l o c k i n g of D for oxygen and sodium i n the g i l l s , i t could a l t e r n a t e l y be hypothesized that the only e f f l u x process present i s simple d i f f u s i o n . Thus an approximately 5-fold e l e v a t i o n of sodium e f f l u x d i d i n fa c t occur, but the techniques used were incapable of detecting most of t h i s increase. Such a s i t u a t i o n can occur i f a back-transport pump i s operative, as has been postulated i n the ammocoete, Lampetra p l a n e r i (Morris and Bull,1970). Under t h i s system, escaping i n t e r n a l sodium ions d i f f u s i n g through the branchial t i s s u e are back-transported toy the unsaturated active sodium pump before they can e f f e c t i v e l y enter the ex-te r n a l medium. ' Adrenaline stimulates the net sodium uptake of the i s o l a t e d perfused trout g i l l (Richards and Fromm,1970). In the present study, no increase i n i n f l u x was observed during exercise when plasma adrenaline l e v e l s are known to r i s e (Nakano and Tomlinson,1967). This r e s u l t could well be explained by back-transport i n the following manner. Active inward transport of sodium was i n fa c t augmented by the stim-u l a t o r y action of catecholamines during a c t i v i t y , but t h i s 70 a d d i t i o n a l a c t i v i t y was o c c u p i e d i n b a c k - t r a n s p o r t i n g i o n s m o v i n g o u t t h r o u g h i n c r e a s e d s i m p l e d i f f u s i o n . C o n s e q u e n t l y no i n c r e a s e i n i n f l u x and o n l y a r e l a t i v e l y s m a l l e l e v a t i o n ( 7 0 % ) o f e f f l u x were o b s e r v e d . A g a i n s t t h i s a r g u m e n t , h o w e v e r , must be s t a t e d t h e f a c t t h a t t h e s i t e s o f maximum d i f f u s i o n a l l o s s ( r e s p i r a t o r y l a m e l l a e ) a n d o f a c t i v e t r a n s p o r t ( i n t e r -l a m e l l a e f i l a m e n t a l e p i t h e l i u m ) a r e s p a t i a l l y s e p a r a t e d i n t h e t e l e o s t g i l l ( C o n t e , 1 9 6 9 ) . I f t h e a s s u m p t i o n s on w h i c h t h e a b o v e a r g u m e n t s a r e b a s e d a r e v a l i d , t h e n t h e r e a l s i t u a t i o n s h o u l d be r e p r e s e n t -a t i v e o f e i t h e r C a s e 1, C a s e 2, o r some c o m b i n a t i o n o f t h e two s c h e m e s . I f t h e a s s u m p t i o n s a r e i n v a l i d , t h e n some comp-l e t e l y d i f f e r e n t m e c h a n i s m c o u l d be i n v o l v e d . The most t e n u o u s s u p p o s i t i o n u s e d i n t h e s e c o n s i d e r a t i o n s i s t h a t o f c o - v a r i a t i o n i n o x y g e n and s o d i u m d i f f u s i o n a l c o e f f i c i e n t s , on w h i c h t h e r e a p p e a r s t o be no r e l e v a n t e v i d e n c e . I n a s y s t e m w h e re g a s e s c a n move d i r e c t l y t h r o u g h t h e p l a s m a membrane b u t i o n s must p a s s t h r o u g h r e s t r i c t i v e " p o r e s " , i t i s p o s s i b l e t o i m a g i n e t h a t r e c r u i t m e n t o f new e x c h a n g e a r e a d u r i n g a c t i v i t y c o u l d c h a n g e one c o e f f i c i e n t more t h a n t h e o t h e r . U n t i l more i s known a b o u t t h e p h y s i c a l p r o p e r t i e s o f t h e g i l l s , c o n s i d e r -a t i o n o f t h i s s u b j e c t w i l l r e m a i n s u p p o s i t i o n . S i m u l t a n e o u s u n i d i r e c t i o n a l f l u x e s o f s o d i u m h a v e n o t p r e v i o u s l y b e e n d e t e r m i n e d ' " a c r o s s t h e g i l l s o f i n t a c t Salmo  g a i r d n e r i , s o c o m p a r i s o n o f t h e p r e s e n t d a t a w i t h r e p o r t e d m e a s u r e m e n t s f o r t h e few o t h e r t e l e o s t s p e c i e s w h i c h h a v e b e e n e x a m i n e d i n f r e s h w a t e r seems w o r t h w h i l e ( T a b l e I V ) . F o r t h e s a k e o f c o n v e n i e n c e , f l u x r a t e s h a v e b e e n e x p r e s s e d i n b o t h ug/100 g / m i n . and uEq/100 g / h r . , t h e u n i t p o p u l a r i z e d b y M a e t z T a b l e IV. S p e c i e s Salmo  g a i r d n e r i S a l v e l i n u s  f o n t i n a l i s Salmo s a l a r ( s m o l t s ) Fundulus  h e t e r o c l i t u s Fundulus  h e t e r o c l i t u s P l a t i c h t h y s  f l e s u s P l a t i c h t h y s  f l e s u s A n g u i l l a  a n g u i l l a A n g u i l l a  a n g u i l l a C a r a s s i u s  a u r a t u s C a r a s s i u s a u r a t u s Summary o f b r a n c h i a l u n i d i r e c t i o n a l sodium f l u x r a t e s i n f r e s h water t e l e o s t s . Weight (g) I n f l u x r a t e E f f l u x r a t e I n f l u x r a t e E f f l u x r a t e E x t . N a + R e f e r e n c e uEq/lOOg/hr UEq/lOOg/hr ug/lOOg/min ug/lOOg/min mEq/L 180-350 0.91-7.72 20-45 2.0-5.0 9 - 2 0 85-115 60-220 107-378 60-120 300-670 80-330 46.0 59.5 68.0 58.0 23.0 12.4 14.0 21.3 4.0 21.4 20.2 44.1 66.0 12.3 19.4 17.6 22.8 26.0 22.2 8.8 4.7 5.4 8.2 1.5 8.2 7.7 16.9 0.07 p r e s e n t s t u d y 0.10 Packer & Dunson(1970) 25.3 0.20 P o t t s e t a l . (1970) 1.00 P o t t s & Evans(1967) 1.00 Maetz e t a l . (1967b) 0.43 M o t a i s & Maetz(1964) - 0.45 M o t a i s e t a l . (1966T 0.55 Garcia-Romeu, Motais(1966) 0.12 Maetz et. a l . (1967a) 4.7 0.70 Maetz(1956) 7.4 0.90 Garcia-Romeu & Maetz(1964) Table IV (Continued) Species Carassius  auratus Carassius  auratus Carassius  auratus Carassius auratus Weight (g) Influx rate E f f l u x rate Influx rate E f f l u x rate Ext.Na + Reference uEq/lOOg/hr uEq/lOOg/hr ug/lOOg/min ug/lOOg/min mEq/L 80-330 80-225 15-80 40-120 34.1 10.8 16.0 16.8 20.6 14.6 25.0 13.1 4.1 6.1 6.4 7.9 5.6 9.6 0.90 0.65 0.12 0.50 Maetz & Garcia-Romeu (1964) Maetz et a l . (1964aT~ Lahlou et a l . (1969) Lahlou & Sawyer(1969) * E f f l u x rates are not tabulated for many reports as workers f a i l e d to d i s t i n g u i s h between bran c h i a l and whole organism e f f l u x e s . 72 and h i s co-workers. A l l values f a l l within the same order of magnitude, but there i s wide v a r i a b i l i t y , much of which may be ascribed to a s i z e e f f e c t . G i l l area per unit body weight, and presumably the fluxes for which the surface i s responsible, decrease with' i n c r e a s i n g body weight (Muir,1968). Thus on a per 100 g b a s i s , very small f i s h w i l l have apparently greater turnovers than those of l a r g e r animals. Branchial sodium fluxes of 260 g Salmo g a i r d n e r i from the present study were r e l a t i v e l y large and comparable to rates observed i n very small f i s h i n other i n v e s t i g a t i o n s . Even more s u r p r i s i n g i s the f a c t that these high rates for rainbow trout were ascertained at external sodium l e v e l s 1/2 — 1/20 of those used by other workers; over the concentration range normally encountered i n fresh water, there i s a d e f i n i t e p o s i t i v e r e l a t i o n s h i p between i n f l u x rate and external sodium l e v e l s (Maetz,1956; Chester Jones e_t a_l.,1969). The magnitude of both u n i d i r e c t i o n a l fluxes i n the rainbow trout r e l a t i v e to other euryhaline forms (e.g. A n g u i l l a a n g u i l l a , P l a t i c h t h y s flesus) lends support to hypothesis (1) stated previously ( i . e . presence of exchange d i f f u s i o n ) . Further consideration of the mechanisms of sodium exchange i n Salmo g a i r d n e r i w i l l be applied i n Section II when data r e l a t i n g to the concentration dependence of the fluxes are presented. Augmentation of branchial permeability to gases and sodium should also enhance the net osmotic entry of water. Urine production may be considered equivalent to the t o t a l i n f l u x of water as long as the f i s h does not drink (Hickman and Trump,1969). The work of Shehadeh and Gordon (1969) renders t h i s a r e l a t i v e l y safe assumption for rainbow t r o u t . Urine 73 F i g u r e 11 Mean u r i n e flow r a t e s over the e x p e r i m e n t a l p e r i o d s i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . F i r s t hour v a l u e s f o r r e c o v e r y f i s h were o b t a i n e d d u r i n g t h e i r i n i t i a l c h a s i n g t r e a t m e n t . The v e r t i c a l l i n e s r e p r e s e n t - 1 s t a n d a r d e r r o r o f each mean. S t a t i s t i c a l Comparisons: (Numbers r e f e r ' t o means as l a b e l l e d on the graph.) F ss 1.01, n.s. 1 4 2 3 10.0-"E ^acH g 6 . 0 -z 4.0-2.0-n=7 n=8 RESTING 1 ACTIVE n=7 n=7 RECOVERY (isthOJR) 3 RECOVERY te^HOUR) 4 74 f l o w ( F i g . 11) t e n d e d t o r i s e d u r i n g e x e r c i s e and d e c r e a s e d u r i n g r e c o v e r y , a l t h o u g h l a r g e v a r i a b i l i t y i n t h e d a t a p r e -c l u d e d s i g n i f i c a n c e . The h i g h e r p r o d u c t i o n r a t e s by r e c o v e r y t r o u t d u r i n g t h e i r h o u r o f e x e r c i s e t h a n b y a c t i v e f i s h may be a t t r i b u t e d t o t h e c o n t i n u a l r e m o v a l o f f l u i d i n s e r i a l b l o o d s a m p l i n g t h r o u g h o u t t h e e x p e r i m e n t a l p e r i o d i n t h e l a t t e r g r o u p . The e f f e c t o f e x e r c i s e on u r i n e f l o w a n d w a t e r f l u x e s h a s b e e n e x a m i n e d i n much g r e a t e r d e t a i l i n S e c t i o n I I I so t h e t o p i c w i l l n o t be p u r s u e d a t p r e s e n t . C. The E f f e c t o f E x e r c i s e on Sodium and W a t e r D i s t r i b u t i o n Many o f t h e r e s u l t s p r e s e n t e d i n t h i s s e c t i o n were o b t a i n e d t h r o u g h t h e s e r i a l r e m o v a l o f s m a l l b l o o d s a m p l e s f r o m t h e f i s h v i a t h e d o r s a l a o r t i c c a t h e t e r . I n t e r p r e t a t i o n o f t h e s e v a l u e s i s c o m p l i c a t e d b y t h e e f f e c t o f t h e r e p e t i t i v e b l o o d r e m o v a l n e c e s s a r y t o a s c e r t a i n them. The s l i g h t f a l l i n b l o o d p r e s s u r e o v e r t h e e x p e r i m e n t a l h o u r i n r e s t i n g f i s h ( T a b l e I) i m p l i e s t h a t t h e r e r e s u l t e d some d e c r e a s e i n b l o o d v o l u m e . H e m a t o c r i t d a t a ( F i g . l 2 ) w e r e i n f o r m a t i v e i n t h i s r e s p e c t f o r i t was i m p r o b a b l e t h a t t h e t r o u t c o u l d m o b i l i z e e r y t h r o c y t e s t o r e p l a c e s a m p l i n g l o s s e s o v e r t h e sh o r t , e x p e r i -m e n t a l t i m e p e r i o d ( S t e v e n s 1968 b ) . I f t h e a n i m a l ' s b l o o d v o l u m e s i m p l y d e c r e a s e d as a f u n c t i o n o f t h e amount r e m o v e d , t h e n t h e r e w o u l d h a v e o c c u r r e d no n e t c h a n g e i n r e d c e l l c o n c e n t r a t i o n . On t h e c o n t r a r y , p a c k e d r e d c e l l v o l u m e s d e c l i n e d p r o g r e s s i v e l y o v e r t h e s a m p l i n g p e r i o d i n a l l t h r e e g r o u p s ( F i g . 1 2 ) ; t h e f i s h must h a v e o b v i o u s l y e f f e c t e d comp-e n s a t o r y c h a n g e s t o h e l p m a i n t a i n t h e c i r c u l a t o r y v o l u m e . The d i f f e r e n c e i n u r i n e f l o w s b e t w e e n t h e r e c o v e r y g r o u p d u r i n g 75 F i g u r e 12 C h a n g e s i n h e m a t o c r i t o v e r t h e e x p e r i m e n t a l p e r i o d s i n r e s t i n g , a c t i v e , a n d r e c o v e r y g r o u p s o f t r o u t . Means - 1 s t a n d a r d e r r o r . 2CH 15H Resting 10- _ j 60 0 15 30 45 ^ 2CH Active 20H i i 10-1 L. Recovery 60 75 90 TIME (MINUTES) 105 120 76 t h e i r h o u r o f e x e r c i s e ( o n l y 0.16 m l / b l o o d / f i s h removed) and t h e a c t i v e g r o u p (1.20 m l / b l o o d / f i s h removed) i n d i c a t e d t h a t t h i s o c c u r r e d a t l e a s t p a r t i a l l y t h r o u g h w a t e r r e t e n t i o n . F l u i d s h i f t s f r o m t h e i n t r a c e l l u l a r t o e x t r a c e l l u l a r p h a s e s ( H o u s t o n , 1 9 64) c o u l d a l s o h a v e b e e n i m p o r t a n t i n t h i s r e s p e c t . T h u s i n a l l t h r e e g r o u p s , p l a s m a c o n s t i t u e n t s were e x p e c t e d t o h a v e u n d e r g o n e some p r o g r e s s i v e d i l u t i o n d u r i n g t h e e x p e r i -ment. However, as s a m p l i n g r e g i m e s were s i m i l a r i n a l l e x p e r i m e n t s , t h e n t h e r e l a t i v e d i f f e r e n c e s o b s e r v e d s h o u l d s t i l l be v a l i d . H e m a t o c r i t c h a n g e s a l s o p r o v i d e d a b a s i s f o r e s t i m a t i o n o f t h e e f f e c t i v e b l o o d v o l u m e o r m i x i n g p o o l f r o m w h i c h s a m p l e s w e r e r e m o v e d o v e r a p a r t i c u l a r i n t e r v a l . I f , f o r t h e p u r p o s e s o f c o m p a r i s o n , t h e a s s u m p t i o n was t a k e n t h a t v o l u m e d i d n o t d e c l i n e i n r e s p o n s e t o s a m p l i n g , t h e n t h e s i z e o f t h e b l o o d p o o l c o u l d be c a l c u l a t e d : Y = b l o o d p o o l / 1 0 0 g 100 ( H i Y - Hx ZV) = Y H * = i n i t i a l h e m a t o c r i t 100 100 Hx = a v e r a g e h e m a t o c r i t o f s a m p l e s b e t w e e n H i and H f H f ( i n c l u d i n g H i ) r H f = f i n a l h e m a t o c r i t 2Tv = t o t a l v o l u m e o f b l o o d removed/100 g b e t w e e n H i and H f ( i n c l u d i n g t h e H i s a m p l e ) B e c a u s e t h e a s s u m p t i o n was n o t e n t i r e l y t r u e , t h e c o m p a r t m e n t s c a l c u l a t e d may r e p r e s e n t o v e r - e s t i m a t i o n s . N e v e r t h e l e s s , t h e y a l l o w l e g i t i m a t e c o m p a r i s o n s o f b l o o d p o o l s i z e s b e t w e e n d i f f -e r e n t t r e a t m e n t g r o u p s and e x p e r i m e n t a l i n t e r v a l s on a r e l a t i v e b a s i s . The b l o o d p o o l s c a l c u l a t e d f r o m t h e h e m a t o c r i t d e c l i n e o v e r 0 - 3 0 m i n u t e s ( o r 60 - 90 m i n u t e s ) and o v e r 15 - 60 m i n u t e s ( o r 75 - 120 m i n u t e s ) a r e p r e s e n t e d i n T a b l e V. T h e s e v a l u e s , 77 T a b l e V. E f f e c t i v e b l o o d p o o l s c a l c u l a t e d from h e m a t o c r i t changes over the f i r s t 30 and f i n a l 45 minute p e r i o d s o f the expe r i m e n t s . E f f e c t i v e b l o o d p o o l s (ml/100 g) R e s t i n g (N = 9) F i r s t measurement 0 - 30 . . o r 6 0 - 9 o m i n u t e s + 1.98 - 0.19 Second measurement 1 5 - 6 0 . ^ o r 7 5 _ 1 2 0 m i n u t e s 2.78 - 0.38 p < 0.10 A c t i v e (N = 9) 1.81 - 0.22 2.01 - 0.34 p = n.s. Recovery (N = 11) 1.82 - 0.35 2.83 - 0.39 p< 0.10 p = s i g n i f i c a n c e w i t h r e s p e c t t o f i r s t measurement. d e s p i t e t h e p r o b a b l e e x a g g e r a t i o n i n h e r e n t i n t h e c o m p u t a t i o n , a r e i n f e r i o r t o t o t a l b l o o d v o l u m e f i g u r e s o b t a i n e d b y d i r e c t m e a s u r e m e n t i n s a l m o n i d s ( S m i t h and B e l l , 1 9 6 4 ; S m i t h , 1 9 6 6 ; H o u s t o n and D e w i l d e , 1 9 6 9 ) . I t i s p o s s i b l e t h a t t h e d i s t r i b -u t i o n v o l u m e " o f e r y t h r o c y t e s i s l o w e r t h a n t h a t o f t h e w h o l e b l o o d due t o " s k i m m i n g " i n c a p i l l a r y b e d s ; C o n t e (1963) i n f a c t m e a s u r e d l o w e r b l o o d v o l u m e s w i t h l a b e l l e d r e d b l o o d c e l l s t h a n w i t h l a b e l l e d p l a s m a p r o t e i n s . However, a more l i k e l y e x p l a n a t i o n may be f o u n d i n t h e work o f S m i t h (1966) who d e m o n s t r a t e d t h a t t h e b l o o d v o l u m e o b t a i n e d was d e p e n d e n t on t h e t i m e a l l o w e d f o r m i x i n g o f t h e l a b e l i n t h e c o m p a r t m e n t . H i s d y e d i l u t i o n c u r v e s e x h i b i t e d one, a n d o c c a s i o n a l l y two , c h a n g e s i n s l o p e b e f o r e s t a b i l i z a t i o n 2 - 3 h o u r s a f t e r i n j e c -t i o n o f t h e m a r k e r . T h e s e s h i f t s were p r o b a b l y r e f l e c t i v e o f p o o l s w i t h d i f f e r e n t t u r n o v e r r a t e s c o m p r i s i n g t h e t o t a l c i r c u l a t i o n , a f a s t m i x i n g p o o l i n t h e l a r g e r v e s s e l s , and a t l e a s t one s l o v ; m i x i n g c o m p a r t m e n t i n t h e p e r i p h e r a l c a p i l l -a r i e s . T he p r e s e n t v a l u e s ( T a b l e V) w e r e t a k e n o v e r o n l y 30 a n d 45 m i n u t e " m i x i n g " i n t e r v a l s , a n d t h e r e f o r e p r o b a b l y d e a l t l a r g e l y w i t h t h e f a s t e q u i l i b r a t i n g p o o l o f t h e m a j o r a r t e r i e s a n d v e i n s . As t h e r e c o u l d be no d i s t i n c t d i v i s i o n b e t w e e n t h e component p o o l s , t h e v o l u m e s d e t e r m i n e d o v e r a s h o r t i n t e r v a l w o u l d be d e p e n d e n t on t h e t i m e a l l o w e d f o r i n t e r c h a n g e . T h u s t h e g r e a t e r v o l u m e s (p < 0.1) f o r t h e s e c o n d m e a s u r e d p e r i o d (45 m i n u t e s ) i n r e s t i n g a n d a c t i v e t r o u t ( T a b l e V) were a t t r i b u t a b l e t o t h i s t i m e d e p e n d e n t m i x i n g e f f e c t . The f a c t t h a t t h i s i n c r e a s e d i d n o t o c c u r i n t h e a c t i v e f i s h was i n d i c a t i v e o f a v o l u m e r e d u c t i o n o f t h e p o o l . S t e v e n s (1968 a) i n f a c t o b s e r v e d a h a e m o c o n c e n t r a t i o n a s s o c -i a t e d w i t h e x e r c i s e i n Salmo g a i r d n e r i w h i c h he, a t t r i b u t e d t o a d e c r e a s e i n t h e w a t e r c o n t e n t o f t h e v a s c u l a r f l u i d s . The d a t a o f S e c t i o n I I I i n d i c a t e s t h a t t h i s b l o o d v o l u m e r e d u c t i o n d u r i n g swimming was c a u s e d b y an i m b a l a n c e b e t w e e n n e t w a t e r i n f l u x a n d e f f l u x , u r i n a r y o u t p u t e x c e e d i n g b r a n c h i a l i n f l u x . V a r i a t i o n s i n p l a s m a s o d i u m l e v e l s o v e r t h e e x p e r i -m e n t a l p e r i o d a r e p r e s e n t e d i n F i g . 13. P r e - e x p e r i m e n t a l c o n c e n t r a t i o n s ( z e r o t i m e ) w e r e i d e n t i c a l t o t h o s e r e p o r t e d b y Toews (1969) f o r r a i n b o w s a f t e r l o n g t e r m a c c l i m a t i o n t o 1 4 ° - 1 6 ° C . D a t a v a r i a b i l i t y p r e c l u d e d s i g n i f i c a n c e , b u t t h e r e was a p r o g r e s s i v e f a l l i n p l a s m a s o d i u m c o n c e n t r a t i o n i n r e s t i n g t r o u t ; t h i s t r e n d was p r o b a b l y e f f e c t e d b y t h e d i l u t i o n o f s e r i a l s a m p l i n g . D u r i n g a c t i v i t y , h o w e v e r , t h i s d i m i n u t i o n f a i l e d t o o c c u r , d e s p i t e t h e e x i s t e n c e o f i n c r e a s e d b r a n c h i a l ( T a b l e I I I ) a n d r e n a l ( S e c t i o n I I I ) s o d i u m l o s s i n a d d i t i o n t o t h e s y s t e m a t i c i t f i t h d r a w a l o f b l o o d . I n r e c o v e r y t r o u t , w h i c h w e r e n o t s a m p l e d d u r i n g t h e f i r s t h o u r , t h e r e was i n f a c t an i n c r e a s e i n p l a s m a s o d i u m l e v e l s d u r i n g e x e r c i s e f o l l o w e d b y a s i g n i f i c a n t d e c l i n e o v e r t h e p o s t - e x e r c i s e h o u r . A n a l y s e s o f t i s s u e s a m p l e s p r o v i d e no e v i d e n c e f o r t h e move-ment o f i n t r a c e l l u l a r s o d i u m i n t o t h e v a s c u l a r c o m p a r t m e n t d u r i n g e x e r c i s e , s o t h e p l a s m a s o d i u m r i s e a s s o c i a t e d w i t h a c t i v i t y may be a t t r i b u t e d t o a r e d u c t i o n , c o m p u t e d p r e v i o u s l y , i n b l o o d v o l u m e t h r o u g h i n e q u a l i t y o f n e t w a t e r f l u x e s . T h i s c o n c e p t i s s u p p o r t e d b y t h e work o f Rao (1969) who f o u n d a s i g n i f i c a n t i n c r e a s e i n p l a s m a o s m o l a r i t y a f t e r e x e r c i s e i n r a i n b o w t r o u t . Rao p o s t u l a t e d t h a t t h i s o s m o c o n c e n t r a t i o n was r e l a t e d t o t h e i n c r e a s e d r e l e a s e o f m e t a b o l i t e s d u r i n g 80 F i g u r e 13 C h a n g e s i n p l a s m a s o d i u m c o n c e n t r a t i o n o v e r t h e e x p e r i m e n t a l p e r i o d s i n r e s t i n g , a c t i v e , a n d r e c o v e r y g r o u p s o f t r o u t . Means - 1 s t a n d a r d . e r r o r . S t a t i s t i c a l C o m p a r i s o n s : (Numbers r e f e r t o t h e s a m p l e t i m e s o f t h e r e s p e c t i v e means.) R e s t i n g : F = 0.52, n . s . 60 15 45 30 5 0 A c t i v e : F = 0.15, n . s . 15 45 5 60 0 30 R e c o v e r y : F = 2.31, p < . 0 5 120 105 90 75 0 65 60 81 a c t i v i t y , b u t d i d m e a s u r e a s l i g h t e l e v a t i o n o f p l a s m a c h l o r i d e l e v e l s ; h i s r e s u l t s c a n w e l l be e x p l a i n e d b y a r e d u c t i o n o f p l a s m a w a t e r . F a r m e r a n d B e a m i s h ( 1 9 6 9 ) , h o w e v e r , o b s e r v e d a n o n - s i g n i f i c a n t d r o p i n o s m o l a r i t y a f t e r e x e r c i s e i n f r e s h w a t e r a d a p t e d T i l a p i a n i l o t i c a ; i n t h i s s p e c i e s , t h e r e may be a g r e a t e r l o s s o f e l e c t r o l y t e s a c r o s s t h e b r a n c h i a l e p i t h e l i u m a n d / o r l e s s e r a b i l i t y o f t h e k i d n e y t o h a n d l e w a t e r l o a d s . T e r m i n a l c o n c e n t r a t i o n s o f s o d i u m and w a t e r i n p l a s m a a n d t i s s u e a r e s u m m a r i z e d i n T a b l e V I . T h e r e o c c u r r e d no s i g n i f i c a n t d i f f e r e n c e b e t w e e n t h e t h r e e g r o u p s i n any o f t h e p a r a m e t e r s m e a s u r e d , d e s p i t e t h e p r e d i c t i o n o f l o w e r p l a s m a w a t e r l e v e l s i n e x e r c i s e d t r o u t b y t h e p r e c e d i n g s t a t e m e n t s . However p l a s m a w a t e r v a l u e s were h i g h e r t h a n p r e v i o u s m e a s u r e -m e n ts i n s a l m o n i d s ( H o u s t o n , 1 9 5 9 ; S t e v e n s , 1 9 6 8 a; M i l e s a n d S m i t h , 1 9 6 8 ; Toews,1969) p r o b a b l y due b o t h t o t h e d i l u t i o n o f s e r i a l s a m p l i n g a n d t h e p r o t e i n c a t a b o l i s m a s s o c i a t e d w i t h p r e -e x p e r i m e n t a l s t a r v a t i o n . D i f f e r e n c e s i n w a t e r c o n c e n t r a t i o n s u f f i c i e n t t o e x p l a i n t h e s l i g h t l y h i g h e r t e r m i n a l p l a s m a s o d i u m l e v e l s i n a c t i v e f i s h w o u l d h a v e f a l l e n w e l l b e l o w t h e a n a l y t i c a l a c c u r a c y o f t h e r e f r a c t o m e t e r . I n an a t t e m p t t o d e t e c t c h a n g e s i n p l a s m a w a t e r l e v e l s d u r i n g e x e r c i s e w i t h o u t t h e c o n f o u n d i n g e f f e c t s o f r e p e t i t i v e s a m p l i n g , t h e z e r o t i m e a n d 60 m i n u t e s a m p l e s f r o m r e c o v e r y f i s h w ere a n a l y z e d i n a number o f e x p e r i m e n t s . The r e s u l t s w e r e e n c o u r a g i n g , b u t n o t c o n c l u s i v e : w a t e r c o n c e n t r a t i o n d e c r e a s e d i n f o u r t r o u t , i n c r e a s e d i n two, a n d r e m a i n e d s t a b l e i n o n e . The d i f f e r e n c e i n t h e means (96.48 ml/100 g p l a s m a v s . 96.30 ml/100 g p l a s m a ) was s u f f i c i e n t t o a c c o u n t f o r t h e o b s e r v e d e l e v a t i o n o f p l a s m a 8 2 T a b l e V I . T e r m i n a l c o n c e n t r a t i o n s o f sodium and water i n plasma and t i s s u e . Means - 1 s t a n d a r d e r r o r . R e s t i n g A c t i v e Recovery T e r m i n a l plasma sodium conc'n. (mEq/L) N = 1 0 1 1 5 . 0 5 - 2 . 7 1 N ss 7 N ss 9 1 2 0 . 6 4 - 3 . 9 7 1 1 5 . 1 9 ± 2 . 8 7 P , ss P . P . p^ ss n.s, P 2 = n.s, T i s s u e sodium c o n c e n t r a t i o n (mEq/kg wet t i s s u e ) N ss 9 8 . 1 3 - 0 . 5 1 N 1 1 N ss 1 1 8 . 9 3 - 0 . 5 1 8 . 0 3 - 0 . 5 0 P 1 = n.s. p^ =s n.s. p_ = n.s. Plasma water N = 1 0 N = 1 1 N = 1 1 c o n c e n t r a t i o n (ml/lOOg plasma) c o n c e n t r a t i o n 9 6 . 9 0 ± 0 . 2 9 9 7 . 1 5 - 0 . 1 4 9 6 . 8 5 ± 0 . 2 0 p^ ss n.s. p^ = n.s. P 2 •= n.s. T i s s u e water N = 1 0 N = 1 1 N = 1 1 ? ° w ? n n r a ^ ° n \ 8 1 . 4 2 0 ± 0 . 3 2 9 8 1 . 5 6 9 ± 0 . 4 5 2 8 2 . 1 0 7 ± 0 . 3 9 9 iml/lUOg t i s s u e ) ss n.s. p^ ss n.s. P 2 = n.s. Sodium space N = 9 N = 1 1 N = 1 1 f g ^ a t e r / k g / w e t 7 2 . 3 8 ± 3 . 9 9 7 6 . 5 7 ± 4 . 8 0 7 1 . 1 4 ± 3 . 7 1 weight) s n.s. = n.s, P 2 = n.s. p^ s= s i g n i f i c a n c e w i t h r e s p e c t t o c o r r e s p o n d i n g r e s t i n g v a l u e , P 2 = s i g n i f i c a n c e w i t h r e s p e c t t o c o r r e s p o n d i n g a c t i v e v a l u e . s o d i u m l e v e l s . S t e v e n s (1968 a) w i t n e s s e d a t r i p h a s i c f l u c t u -a t i o n i n p l a s m a w a t e r l e v e l s a t t h e o n s e t o f e x e r c i s e i n t r o u t , c u l m i n a t i n g i n a f i n a l g r a d u a l d e c r e a s e as swimming t i m e was p r o l o n g e d . T i s s u e w a t e r l e v e l s were a b o u t 2% h i g h e r t h a n commonly q u o t e d v a l u e s f o r s a l m o n i d s ( H o u s t o n , 1 9 5 9 ; H o u s t o n e t al.,1968; Toews, 1969) ; a g a i n t h e h y d r a t i o n was a p r o b a b l e c o n s e q u e n c e o f s t a r v a t i o n ( B r e t t , p e r s o n a l c o m m u n i c a t i o n ) , t h e a p p a r e n t l y h i g h e r w a t e r c o n t e n t s b e i n g due t o a r e d u c t i o n i n t h e f a t c o n t e n t o f t h e t i s s u e s . M u s c l e s o d i u m l e v e l s , h o w e v e r , a g r e e d w e l l w i t h p r e v i o u s l y r e p o r t e d f i g u r e s (Toews,1969) f o r r a i n b o w s a c c l i m a t e d a t 1 4 ° - 1 6 ° C . As t h e r e i s l i t t l e i n t r a -c e l l u l a r s o d i u m ( M a n e r y , 1 9 5 4 ) , m u s c l e s o d i u m s h o u l d be l a r g e l y r e f l e c t i v e o f c o n c e n t r a t i o n s i n p l a s m a . I n b o t h r e s t i n g and r e c o v e r y g r o u p s , t h e r e o c c u r r e d s i g n i f i c a n t p o s i t i v e c o r r e l -a t i o n s ( r = 0.754, p < .01; r = 0.678, p <. .05 r e s p e c t i v e l y ) b e t w e e n p l a s m a a n d t i s s u e l e v e l s o f t h e e l e c t r o l y t e i n i n d i v i -d u a l a n i m a l s . T h i s r e l a t i o n s h i p , h o w e v e r , d i d n o t e x i s t f o r a c t i v e t r o u t ( r = .033, n . s . ) i n d i c a t i n g a p o s s i b l e b u f f e r i n g d u r i n g e x e r c i s e o f t h e t i s s u e s f r o m c h a n g e s i n e l e c t r o l y t e l e v e l s i n t h e f a s t - m i x i n g p l a s m a p o o l . An i s c h e m i a o f " w h i t e " m u s c l e d u r i n g swimming ( S t e v e n s , 1 9 6 8 b) w o u l d be a p r o b a b l e c a u s e f o r t h e phenomenon; a d d i t i o n a l e v i d e n c e f o r t h i s phenom-• 22 e n o n was p r o v i d e d b y Na d i s t r i b u t i o n d a t a w h i c h w i l l be d i s c u s s e d p r e s e n t l y . As t h e p a r a m e t e r s f r o m w h i c h t h e s o d i u m s p a c e e s t i m a t e o f e x t r a c e l l u l a r f l u i d v o l u m e were c a l c u l a t e d d i d n o t show s i g n i f i c a n t v a r i a t i o n , E . C . F . V ' s w e r e s i m i l a r i n a l l t h r e e t r e a t m e n t g r o u p s . Toews (1969) h a s d e m o n s t r a t e d t h a t i n f r e s h w a t e r t e l e o s t s , u n l i k e mammals, s o d i u m s p a c e p r o v i d e s a more a c c u r a t e m e a s u r e o f E . C . F . V . t h a n c h l o r i d e o r c h l o r i d e - p o t a s s i u m s p a c e b e c a u s e o f t h e s i g n i f i c a n t c h l o r i d e c o n t e n t o f t h e i n t r a c e l l u l a r p h a s e . 22 The e v o l u t i o n o f t h e Na s p a c e w i t h t i m e d u r i n g r e s t , a c t i v i t y , a n d r e c o v e r y i s i l l u s t r a t e d i n F i g . 14, w h i l e t h e t e m p o r a l s e q u e n c e o f t h e a c c u m u l a t i o n i n p l a s m a o f s o d i u m t r a n s p o r t e d f r o m t h e e x t e r n a l w a t e r ("plasma s o d i u m i n c o r p o r a t i o n " ) i s p r e s e n t e d i n F i g . 15. P l a s m a s o d i u m i n c o r p o r a t i o n i s a 22 f a c t o r w h i c h p e r m i t s t h e c o m p a r i s o n o f p l a s m a Na l e v e l s b e t w e e n i n d i v i d u a l f i s h , w h i c h w o u l d n o t be v a l i d t h r o u g h u s e o f j u s t a c t i v i t y v a l u e s due t o d i f f e r e n c e s i n e x t e r n a l s p e c -i f i c a c t i v i t y b e t w e e n e x p e r i m e n t s . As s u c h , t h i s f a c t o r i s 22 t h e r a t i o b e t w e e n p l a s m a Na l e v e l s a n d t h e a v e r a g e e x t e r n a l s p e c i f i c a c t i v i t y p r i o r t o t h e m e a s u r e m e n t t i m e . T h u s v a l u e s a r e e x p r e s s e d i n t e r m s o f t h e a c t u a l c o n c e n t r a t i o n o f s o d i u m f r o m t h e e x t e r n a l medium r e s i d e n t i n t h e i n t e r n a l medium a t t h e p a r t i c u l a r s a m p l e t i m e . The a n a l o g o u s v a l u e s f o r t i s s u e ( " t i s s u e s o d i u m i n c o r p o r a t i o n " ) a r e s u m m a r i s e d i n T a b l e V I I t o g e t h e r w i t h t h e r a d i o s o d i u m s p a c e a n d p l a s m a s o d i u m i n c o r p -o r a t i o n v a l u e s a t 60 ( o r 120) m i n u t e s f o r e a c h e x p e r i m e n t a l g r o u p . T h e t i m e c o u r s e o f t h e r a d i o s o d i u m s p a c e e x p a n s i o n i n t e l e o s t s h a s b e e n f o l l o w e d i n o n l y one o t h e r s t u d y (Mayer a n d N i b e l l e , 1 9 6 9 ) w h i l e t h e r e l a t i v e i n c o r p o r a t i o n o f e x t e r n a l s o d i u m i n t o p l a s m a a n d t i s s u e r e p r e s e n t s a c o m p l e t e l y new a p p r o a c h . - I n t e r p r e t a t i o n o f t h f s e d a t a must t h e r e f o r e p r o c e e d f r o m a b a s i c l e v e l . The f o r m o f t h e e v o l u t i o n c u r v e ( F i g . 14) i s s i m i l a r i n t h e t h r e e t r e a t m e n t s a l t h o u g h t h e m a g n i t u d e s o f t h e component p o i n t s d i f f e r b e t w e e n e x p e r i m e n t a l g r o u p s . 85 F i g u r e 14 The e v o l u t i o n o f the r a d i o s o d i u m space w i t h time i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . Means - 1 s t a n d a r d e r r o r . A s= s i g n i f i c a n t l y d i f f e r e n t from c o r r e s p o n d i n g r e s t i n g v a l u e (p < .05) Resting TIME (MINUTES) 86 F i g u r e 15 The e v o l u t i o n with time o f the c o n c e n t r a t i o n i n plasma o f sodium t r a n s p o r t e d from the e x t e r n a l environment ("plasma sodium i n c o r p o r a t i o n " ) i n r e s t i n g , a c t i v e , and r e c o v e r y groups o f t r o u t . Means - 1 s t a n d a r d e r r o r . A = s i g n i f i c a n t l y d i f f e r e n t from c o r r e s p o n d i n g r e s t i n g v a l u e (p < .05) The g e n e r a l c o n f i g u r a t i o n o f t h e o b s e r v e d c h a n g e s w i l l be d e a l t w i t h f i r s t . By d e f i n i t i o n , t h e r a d i o s o d i u m s p a c e i s t h e r a t i o b e t w e e n t h e amount o f r a d i o i s o t o p e i n t h e w h o l e a n i m a l and t h e . 2 2 amount p e r ml o f p l a s m a . The p r e c i p i t o u s i n c r e a s e m Na d i s t r i b u t i o n v o l u m e o v e r t h e f i r s t 5 m i n u t e i n t e r v a l was p r o b a b l y 22 23 . r e l a t e d t o t h e i n i t i a l e x c h a n g e o f Na i o n s w i t h Na i o n s a d s o r b e d t o t h e s k i n o f t h e a n i m a l . T h i s a p p a r e n t i n f l u x w o u l d t e n d t o e l e v a t e t h e v a l u e o f t h e t e r m (Qo - Q) ( s e e M e t h o d s p . 3 8 ) d i s p r o p o r t i o n a t e l y t o t h e r a d i o a c t i v i t y o f t h e p l a s m a 22 (Na /ml p t ) , t h e r e b y e x a g g e r a t i n g t h e c a l c u l a t e d d i s t r i b u t i o n s p a c e . A r r i v a l o f t h e e x p a n s i o n c u r v e a t a z e n i t h , o r a t l e a s t a p l a t e a u , 45 m i n u t e s a f t e r i n t r o d u c t i o n o f r a d i o t r a c e r , 22 i s h o w e v e r , more d i f f i c u l t t o e x p l a i n , f o r t h e v o l u m e o f Na d i s t r i b u t i o n a t e q u i l i b r i u m i s a b o u t 34 ml/100 g ( S e c t i o n I I ) , c o n s i d e r a b l y g r e a t e r t h a n t h i s a p p a r e n t p e a k a t 17 - 21 m l s / 1 0 0 g . R e f e r e n c e t o t h e p l a s m a s o d i u m i n c o r p o r a t i o n d a t a ( F i g . 15) p r o v i d e s t h e o b v i o u s m a t h e m a t i c a l e x p l a n a t i o n f o r t h e phenom-e n o n . The e v o l u t i o n c u r v e o f p l a s m a s o d i u m i n c o r p o r a t i o n 2? ( r e p r e s e n t a t i v e o f p l a s m a Na "* c o n c e n t r a t i o n ) u n d e r w e n t an a b r u p t u p w a r d d e f l e c t i o n a t t h e same p o i n t (45 m i n u t e s ) as t h e l e v e l l i n g o f t h e r a d i o s o d i u m s p a c e c u r v e . C o n s e q u e n t l y , t h e r e p r o b a b l y o c c u r r e d a l a r g e i n c r e a s e i n t h e p a r a m e t e r 22 Na /ml p t r e l a t i v e t o t h e r i s e i n (Qo - Q), r e s u l t i n g i n a 22 l o w e r t e r m i n a l e s t i m a t e o f Na d i s t r i b u t i o n v o l u m e . The b i o l o g i c a l r e a s o n f o r t h i s e v e n t , h o w e v e r , r e m a i n s u n c l e a r . Up t o 45 m i n u t e s , t h e s l o p e s o f t h e p l a s m a i n c o r p o r a t i o n c u r v e s t e n d e d t o s l o w l y d e c l i n e as r a d i o s o d i u m became d i s -t r i b u t e d o v e r an i n c r e a s i n g v o l u m e , p r e s u m a b l y t h r o u g h t h e n a t u r a l e n l a r g e m e n t w i t h t i m e o f t h e e f f e c t i v e v a s c u l a r m i x i n g p o o l a n d t h e c o n c o m i t a n t d i f f u s i o n a l d i s p e r s a l t o a g r e a t e r t i s s u e mass. T h e a c c l i v i t y o f t h e c u r v e a f t e r 45 m i n u t e s c o u l d be due t o e i t h e r an i n c r e a s e i n t h e r a t e o f i n f l u x o f e x t e r n a l s o d i u m a c r o s s t h e g i l l s i n t o t h e p l a s m a p o o l , o r a d e c r e a s e i n t h e r a t e o f movement o u t o f t h e p o o l . I t seems u n l i k e l y t h a t t h e r e w o u l d be any s i g n i f i c a n t b a c k f l u x o f i n f l u x e d s o d i u m f r o m t h e t i s s u e s i n t o t h e m i x i n g c o m p a r t m e n t ) . I t h a s a l r e a d y b e e n shown,however, t h a t b r a n c h i a l i n f l u x r a t e r e m a i n e d c o n s t a n t ( F i g . 9) o v e r t h e i n t e r v a l i n q u e s t i o n , so t h e s e c o n d i n t e r p r e t a t i o n must a p p l y . The most p r o b a b l e r e a s o n f o r a d e c r e a s e d r a t e o f movement o u t o f t h e m i x i n g p o o l i s t h a t t h e s i z e o f t h i s c o m p a r t m e n t a p p r o a c h e d o r a t t a i n e d c o n s t a n c y s u c h t h a t d i s p e r s a l o f i n f l u x e d s o d i u m became l i m i t e d b y d i f f u s i o n i n t o t h e e x t r a v a s c u l a r E.C.F.V. s p a c e s and p e r h a p s t h e i n t r a -c e l l u l a r p h a s e . S m i t h ( 1 9 6 6 ) , i n u s i n g t h e d i l u t i o n o f E v a n ' s B l u e d y e t o m e a s u r e b l o o d v o l u m e s i n s a l m o n i d s f o u n d t h a t t h e i n t e r s e c t i o n o f t h e i n i t i a l " m i x i n g p l u s e x c r e t i o n " s l o p e w i t h t h e s t a b l e " e x c r e t i o n " s l o p e o f t h e d y e d i l u t i o n c u r v e t o o k p l a c e " a b o u t one h o u r a f t e r i n j e c t i o n " . A l t h o u g h S m i t h ' s e x p e r i m e n t s d i f f e r e d f r o m t h o s e r e p o r t e d h e r e i n t h e i n c i d e n c e o f o n l y a s i n g l e i n j e c t i o n o f m a r k e r r a t h e r t h a n c o n s t a n t e n t r y o f i t a c r o s s t h e g i l l s , i t i s t e m p t i n g t o s p e c u l a t e t h a t t h e p l a t e a u o f t h e r a d i o s o d i u m s p a c e c u r v e was a t t r i b u t a b l e t o a s i m i l a r s t a b i l i z a t i o n o f t h e m i x i n g comp-a r t m e n t . T h e o n l y p r e v i o u s e x a m i n a t i o n o f r a d i o s o d i u m s p a c e e v o l u t i o n i n t e l e o s t s i s t h a t o f M a y e r and N i b e l l e (1969) i n t h e e e l , A n g u i l l a a n g u i l l a . T h e s e w o r k e r s d e m o n s t r a t e d t h a t 89 t h e r a t e o f c o m p l e t i o n o f t h e r a d i o s o d i u m s p a c e , b u t n o t i t s e q u i l i b r i u m v a l u e , d e p e n d e d upon t h e s i t e o f i n t r o d u c t i o n o f t h e l a b e l . T h e y a r g u e d t h a t c a p i l l a r y b a r r i e r s were n e g l i g i b l e 22 i n t h e e v o l u t i o n o f t h e Na d i s t r i b u t i o n v o l u m e , and t h a t t h e " f i l l i n g u p " o f t h e c o m p a r t m e n t ( r a d i o s o d i u m s p a c e ) c o u l d be l i k e n e d t o t h e d i f f u s i o n o f e l e c t r o l y t e s i n an i o n i z e d s o l u t i o n . The p r e s e n c e o f a p l a t e a u e f f e c t i n t h e p r e s e n t d a t a c a s t s some d o u b t on t h i s i n t e r p r e t a t i o n . However, M a y e r and N i b e l l e (1969) t o o k o n l y w i d e l y s p a c e d s a m p l e s a n d t h u s w o u l d h a v e b e e n u n a b l e t o d e t e c t an i n t e r m e d i a t e l e v e l l i n g o f t h e c u r v e . I n l i g h t o f t h e w i d e s p r e a d u s e o f r a d i o s o d i u m s p a c e v a l u e s as t h e " i n t e r n a l c o m p a r t m e n t " i n t h e c a l c u l a t i o n o f b r a n c h i a l f l u x r a t e s a n d e x c h a n g e a b l e s o d i u m p o o l s ( e . g . M a e t z , 1 9 5 6 ; M o t a i s , 1 9 6 7 ) , more d e t a i l e d s t u d i e s on t h e k i n e t i c s o f r a d i o s o d i u m s p a c e e v o l u t i o n a r e u r g e n t l y r e q u i r e d . U n t i l t h e work o f M a yer and N i b e l l e ( 1 9 6 9 ) , t h e r e h a d a p p a r e n t l y b e e n no s y s t e m -a t i c a t t e m p t t o f i n d e v e n t h e e q u i l i b r i u m v a l u e s o f t h i s p a r a m e t e r i n a p a r t i c u l a r s p e c i e s , d e s p i t e i t s u b i q u i t o u s a p p l i c a t i o n t o t h e s t u d y o f t e l e o s t i o n i c r e g u l a t i o n f o r o v e r t w e l v e y e a r s . F o r e x a m p l e , t h e d a t a o f Wood and R a n d a l l (19 71) i n d i c a t e t h a t t h e commonly u s e d r a d i o s o d i u m s p a c e v a l u e o f t h e f l o u n d e r ( M o t a i s e t a l _ . ,1966; M o t a i s , 1967) , on w h i c h p e r h a p s t h e m a j o r i t y o f i o n e x c h a n g e work h a s b e e n p e r f o r m e d ( M a e t z , 1 9 6 9 ) , may w e l l be a s i g n i f i c a n t u n d e r e s t i m a t i o n o f t h e e q u i l i -b r i u m v o l u m e . 22 D i f f e r e n c e s i n t h e e v o l u t i o n o f t h e Na d i s t r i b u t i o n v o l u m e b e t w e e n t r e a t m e n t g r o u p s may now be e x a m i n e d . The c u r v e s ( F i g . 14) f o r a c t i v e and r e c o v e r y t r o u t f o l l o w e d a s i m i l a r c o u r s e ; h o w e v e r t h e r a d i o s o d i u m s p a c e e x p a n s i o n l a g g e d 90 noticeably behind t h i s pattern during r e s t , the d i f f e r e n c e becoming s i g n i f i c a n t by the terminal sample. It i s not poss-i b l e , however, to say whether the equilibrium values would also have d i f f e r e d ; i n any case, the point i s somewhat hypo-t h e t i c a l as an a c t i v e f i s h would stop swimming at some time, and a recovery f i s h would eventually return to the r e s t i n g 2? c o n d i t i o n . The hxgher Na " d i s t r i b u t i o n volumes during exercise and post~exercise cannot be r e l a t e d d i r e c t l y to the plasma volume changes discussed e a r l i e r for at l e a s t two reasons. F i r s t l y the l a r g e r spaces were c h a r a c t e r i s t i c of both active and recovery s t a t e s , while the reduction of blood volume through dehydration occurred only during exercise (Table V). Secondly,, a decrease i n the s i z e of the plasma 22 volume alone would increase the concentration of Na on a simple d i l u t i o n b a s i s , and, i n addition, would tend to depress the d i f f u s i o n of the isotope out of the vascular pool into the t i s s u e s . The net e f f e c t of hemoconcentration would be an i n h i b i t i o n , rather than a stimulation, of the radiosodium space evolution. Plasma sodium incorporation values ( F i g . 15) -i n d i c a t e that the reverse was i n f a c t true; by the end of the 22 experiment, plasma "Na concentrations" were s i g n i f i c a n t l y lower than the r e s t i n g value i n both active and recovery t r o u t , 22 thereby generating the higher Na d i s t r i b u t i o n volume. It must be noted that t h i s e f f e c t cannot be r e l a t e d to slower entry rates of sodium, for i n f l u x e s were i d e n t i c a l i n a l l three groups (Table IV). Thus there must have occurred a greater emigration rate of previously i n f l u x e d sodium out of the sampled plasma pool during a c t i v i t y and recovery than at r e s t , despite the probable decrease i n s i z e of t h i s compartment d u r i n g e x e r c i s e . T he t e r m i n a l e p a x i a l m u s c l e s a m p l e s were 22 a n a l y z e d f o r Na as a p o s s i b l e r e c e p t i o n s i t e f o r t h i s l o s t s o d i u m ; t h e r e s u l t s , e x p r e s s e d as t i s s u e s o d i u m i n c o r p o r a t i o n on a wet w e i g h t b a s i s , a r e p r e s e n t e d i n T a b l e V I I . " W h i t e " m u s c l e o b v i o u s l y d i d n o t r e c e i v e t h i s e x t r a s o d i u m , t h e i n c o r p -o r a t i o n b e i n g somewhat l o w e r i n t h e a c t i v e t r o u t t h a n i n t h e r e s t i n g a n i m a l , a n d s i g n i f i c a n t l y s m a l l e r i n t h e r e c o v e r y f i s h . ( "White" m u s c l e i s a m i s n o m e r i n s a l m o n i d s , a s Webb ( p e r s o n a l c o m m u n i c a t i o n ) h a s f o u n d t h a t t h i s t i s s u e may c o n t a i n up t o 1 7 % r e d m u s c l e f i b r e s b y v o l u m e ) . The t i s s u e i n c o r p o r a t i o n d a t a i s t h u s r e f l e c t i v e o f p l a s m a i n c o r p o r a t i o n v a l u e s . However, c o r r e c t i o n o f t i s s u e i n c o r p o r a t i o n m e a s u r e m e n t s f o r h y p o t h e t i c a l e n c l o s e d p l a s m a v o l u m e s o f 1 - 4% d i d n o t c h a n g e t h e f a c t t h a t t h e e x t r a v a s c u l a r r e g i o n o f " w h i t e " m u s c l e a c c -u m u l a t e d l e s s i n f l u x e d s o d i u m d u r i n g e x e r c i s e and r e c o v e r y t h a n d u r i n g r e s t . I t must t h e r e f o r e be c o n c l u d e d t h a t t h e h i g h e r r a d i o s o d i u m s p a c e s r e s u l t e d f r o m a g r e a t e r a c c u m u l a t i o n o f i n f l u x e d s o d i u m , a n d t h u s t h e r a d i o i s o t o p e , i n o t h e r r e g i o n s o f t h e b o d y w i t h an a c c o m p a n y i n g d e c r e a s e i n " w h i t e " m u s c l e i n c o r p o r a t i o n . Due t o t h e t i m e l a g i n m o v i n g f r o m t h e g i l l s t o t h e t i s s u e s , t h e m a j o r i t y o f r a d i o s o d i u m f o u n d i n m u s c l e a f t e r 60 m i n u t e s p r o b a b l y e n t e r e d t h e a n i m a l d u r i n g t h e e a r l i e r p o r t i o n o f t h e e x p e r i m e n t a l h o u r when e x t e r n a l s p e c i f i c a c t i v i t i e s w ere g r e a t e s t . U s e o f t h e a v e r a g e e x t e r n a l s p e c i f i c a c t i v i t y f i g -u r e s o v e r t h e w h o l e h o u r t o c a l c u l a t e t i s s u e s o d i u m i n c o r p o r a -t i o n may t h e r e f o r e h a v e b e e n r e s p o n s i b l e f o r a s y s t e m a t i c o v e r -e s t i m a t i o n o f t h i s p a r a m e t e r . However, s u c h an e r r o r w o u l d h a v e b e e n common t o a l l t h r e e g r o u p s , a n d w o u l d i n f a c t t e n d t o 92 T a b l e V I I . M e a s u r e s o f i n t e r n a l d i s t r i b u t i o n o f i n f l u x e d s o d i u m a t 60 m i n u t e s a f t e r i n t r o d u c t i o n o f Na . Means i 1 s t a n d a r d e r r o r , R e s t i n g A c t i v e R e c o v e r y N a 2 2 s p a c e N = 8 N = 9 N = 10 (ml / 1 0 0 g) 15.73 - 1.05 18.45 - 0.70 19.56 - 0.90 (60 m i n u t e s ) p < 0.05 p x <C 0.05 P 2 = n . s . P l a s m a s o d i u m N = 9 . N = 9 N = 10 i n c o r p o r a t i o n 64.86 - 3.83 51.99 - 3.81 49.17 - 4.09 (u g / m l ) P t < 0 . 0 5 p , < 0.02 (60 m i n u t e s ) p 2 = n . s . T i s s u e s o d i u m N = 10 N = 10 N = 10 i n c o r p o r a t i o n 3.077--0.243 2.579 0.351 2.218 - 0.203 ( u g / k g / w e t t i s s u e ) p = n . s # p, <0.02 (60 m i n u t e s ) P 2 = n . s . p ^ = s i g n i f i c a n c e w i t h r e s p e c t t o c o r r e s p o n d i n g r e s t i n g v a l u e . P 2 = s i g n i f i c a n c e w i t h r e s p e c t t o c o r r e s p o n d i n g a c t i v e v a l u e . T a b l e V I I I . B a l a n c e s h e e t o f f a t e o f i n f l u x e d s o d i u m a t 60 m i n -22 u t e s a f t e r i n t r o d u c t i o n o f Na . So d i u m i n f l u x e d / l O O g o v e r 60 m i n u t e s S o d i u m i n c o r p o r a t e d i n p l a s m a (3 ml/100 g) S o d i u m i n c o r p o r a t e d i n t i s s u e (97 g/100 g) T o t a l i n t i s s u e s a n d p l a s m a % o f t o t a l s o d i u m i n f l u x r e p r e s e n t e d R e s t i n g A c t i v e R e c o v e r y 105 7.2 ug 984.6 ug 1154.4 u g 194.6 ug 156.0 u g 147.5 u g 298.5 ug 250.2 u g 215.2 u g 493.1 ug 406.2 ug 362.7 u g 4 6 . 6 4 % 4 1 . 2 5 % 31.42% I t h a s b e e n assumed i n t h e a b o v e c a l c u l a t i o n t h a t a l l t i s s u e s o d i u m i n c o r p o r a t i o n was e q u a l t o " w h i t e " m u s c l e s o d i u m i n c o r p -o r a t i o n a n d t h a t p l a s m a v o l u m e i n t h e m a j o r v e s s e l s was 3 ml/100 g . e n f o r c e t h e s u b s t a n c e o f t h e f o l l o w i n g a r g u m e n t . I f a g e n e r o u s e s t i m a t e o f 3 ml/100 g b o d y w e i g h t f o r p l a s m a i n t h e m a j o r v e s s e l s and t h e a s s u m p t i o n o f t i s s u e i n c o r p o r a t i o n v a l u e s e q u a l t o t h a t o f e p a x i a l m u s c l e f o r t h e r e m a i n d e r o f t h e b o d y mass a r e t a k e n , t h e n t h e b a l a n c e s h e e t s o f T a b l e V I I I may be c o n s t r u c t e d f o r t h e t r o u t i n e a c h g r o u p a t 60 m i n u t e s a f t e r i n t r o d u c t i o n o f t h e i s o t o p e . E v e n a t r e s t , s u c h a scheme a c c o u n t s f o r t h e f a t e o f l e s s t h a n 4 7 % o f t h e i n f l u x e d s o d i u m ; t h i s f i g u r e d e c r e a s e s t o 31.5% i n t h e p o s t -e x e r c i s e c o n d i t i o n . I t i s a p p a r e n t t h a t u n d e r a l l c o n d i t i o n s some t i s s u e s must e x c h a n g e s o d i u m f a s t e r t h a n t h e " w h i t e " m u s c l e , an d t h a t t h i s e f f e c t i s a c c e n t t i a t e d d u r i n g a c t i v i t y and r e c o v e r y by a f u r t h e r r e d u c t i o n o f s o d i u m t u r n o v e r i n " w h i t e " m u s c l e an d an i n c r e a s e i n t h e t u r n o v e r r a t e s o f o t h e r unknown t i s s u e s . The s o d i u m t u r n o v e r r a t e o f a p a r t i c u l a r t i s s u e m i g h t w e l l be p r o p o r t i o n a l t o i t s b l o o d s u p p l y . I f t h i s i s t r u e , t h e n t h e d i s c r e t e r e d m u s c l e an d c a r d i a c m u s c l e , w h i c h , on a u n i t w e i g h t b a s i s , c o n t a i n 2~i t i m e s as much b l o o d as " w h i t e " m u s c l e ( S t e v e n s , 1 9 6 8 a), may p r e f e r e n t i a l l y a c c u m u l a t e s o d i u m . Th e i n c r e a s e d b l o o d f l o w t o t h e s e t i s s u e s d u r i n g e x e r c i s e c o u l d t h e r e f o r e a c c o u n t f o r t h e l o w e r c o n c e n t r a t i o n s o f i n -2 2 f l u x e d s o d i u m i n t h e p l a s m a , an d h i g h e r Na d i s t r i b u t i o n v o l u m e s m e a s u r e d d u r i n g e x e r c i s e . T h i s e f f e c t c o u l d be f u r t h e r a u g m e n t e d b y an i s c h e m i a o f t h e " w h i t e " m u s c l e , as i n d i c a t e d b y t h e r e d u c e d s o d i u m i n c o r p o r a t i o n o f t h i s t i s s u e , and t h e l a c k o f c o r r e l a t i o n b e t w e e n p l a s m a and t i s s u e l e v e l s o f t o t a l s o d i u m d i s c u s s e d p r e v i o u s l y . I t i s d i f f i c u l t , h o w e v e r , t o s e e how t h i s e x p l a n a t i o n c o u l d a l s o a p p l y t o t h e s i m i l a r s o d i u m s p a c e e l e v a t i o n a n d d e c r e a s e d p l a s m a a n d " w h i t e " m u s c l e s o d i u m i n c o r p o r a t i o n d e t e r m i n e d d u r i n g r e c o v e r y , when b l o o d f l o w p a t t e r n s s h o u l d r e t u r n t o a more r e s t i n g c o n f i g u r a t i o n . T h u s 22 b l o o d f l o w v a r i a t i o n may c o n t r i b u t e t o t h e o b s e r v e d Na s p a c e d i f f e r e n c e s , b u t i s p r o b a b l y n o t t h e m a j o r f a c t o r i n v o l v e d . A p r o p e r t y common t o b o t h a c t i v e a n d r e c o v e r y c o n d i t i o n s i s t h e p r e s e n c e o f h i g h c i r c u l a t i n g l e v e l s o f c a t e c h o l a m i n e s (Nakano a n d T o m l i n s o n , 1 9 6 7 ) , s u b s t a n c e s w h i c h a r e known t o s t i m u l a t e t h e a c t i v e t r a n s p o r t o f s o d i u m a c r o s s t r o u t g i l l s i n v i t r o ( R i c h a r d s and Fromm,1970). I t i s p o s s i b l e t h a t t h e s e h o r mones may a l s o p r o m o t e t h e u p t a k e o r t u r n o v e r o f s o d i u m b y s p e c i f i c s i n k s i n t h e s y s t e m , t h e r e b y c o n t r i b u t i n g t o t h e e l e v a t i o n o f r a d i o s o d i u m s p a c e . A g a i n , s u c h s i t e s c o u l d w e l l be t h o s e t i s s u e s c o n t a i n i n g h i g h b l o o d v o l u m e s , s u c h as t h e l i v e r , s p l e e n , r e d m u s c l e , a n d c a r d i a c m u s c l e ( S t e v e n s , 1 9 6 8 a ) . 95 SUMMARY I 1. The v e n t i l a t o r y and cardiovascular responses of trout to chasing i n the present study were s i m i l a r to those reported to occur during normal swimming a c t i v i t y i n other studies. 2. U n i d i r e c t i o n a l branchial sodium fluxes of Salmo g a i r d n e r i v/ere higher than those recorded for other fresh water t e l e o s t s of comparable s i z e despite the extremely low external sodium concentrations used i n t h i s study. 3. The uptake of sodium by the g i l l s was apparently an active transport process. 4. Resting trout maintained a state of sodium equilibrium at the g i l l s . During one hour of exercise there occurred a net branchial sodium l o s s which was reversed during recovery. 5. The a l t e r a t i o n s i n net f l u x rate at the onset of exercise and the onset of recovery occurred extremely r a p i d l y (within 5 minutes). 6. Branchial, sodium i n f l u x r a t e remained constant during r e s t , exercise, and recovery. 7. Branchial sodium e f f l u x rate increased 10% with swimming a c t i v i t y , causing a negative balance s i t u a t i o n . This u n i -d i r e c t i o n a l outward movement decreased to s l i g h t l y below r e s t -ing l e v e l s during one hour recovery. 8. The e l e v a t i o n of e f f l u x apparently occurred through i n -creased simple d i f f u s i o n r e s u l t i n g from an augmented branchial permeability. 9 . C a l c u l a t i o n s based on hematocrit changes suggested that blood volume decreased during exercise. 10. Plasma sodium l e v e l s tended to increase i n exercised f i s h even though there was a net loss of sodium. This e f f e c t was apparently caused by the blood volume decrease. 11. Terminal t i s s u e sodium and water l e v e l s , and sodium space (E.C.F.V.), were s i m i l a r i n r e s t i n g , a c t i v e , and recovery animals. 12. In a l l groups, the evolution of the Na" d i s t r i b u t i o n volume reached a temporary plateau 45 - 60 minutes a f t e r i n t r o -duction of the radioisotope. This l e v e l l i n g e f f e c t corres-ponded to an a c c l i v i t y i n the plasma sodium incorporation curve. 13. Sodium gained from the external environment over the experi mental period was p r e f e r e n t i a l l y accumulated (on a per unit weight basis) i n t i s s u e s other than "white" muscle i n a l l t r e a t ments. 14. Radiosodium space expansion during r e s t lagged behind that occurring under active and recovery conditions, the d i f f e r e n c e becoming s i g n i f i c a n t at 60 minutes a f t e r addition of the tr a c e r The opposite course was seen i n plasma sodium incorporation values, t h i s f a c t o r i n active and recovery f i s h becoming s i g n i f i c a n t l y i n f e r i o r to r e s t i n g values by 60 minutes. A p a r a l l e l trend occurred i n t i s s u e sodium incorporation values for the three groups. Thus greater amounts of i n f l u x e d sodium were taken up by " s i t e s " other than"white"muscle during a c t i v i t y and recovery than during r e s t . 97 SECTION I I THE E F F E C T OF EXTENDED EXERCISE ON SODIUM BALANCE INTRODUCTION I I The e x p e r i m e n t s o f S e c t i o n I d e m o n s t r a t e d t h e o c c u r -r e n c e o f a n e t b r a n c h i a l s o d i u m l o s s d u r i n g e x e r c i s e . The r e s u l t s s t r o n g l y i n d i c a t e d t h a t t h i s n e g a t i v e b a l a n c e was c a u s e d b y an i n c r e a s e d s i m p l e d i f f u s i o n a l e f f l u x due t o a r e a d j u s t m e n t o f e f f e c t i v e g i l l p e r m e a b i l i t y n e c e s s i t a t e d b y t h e i n c r e a s e d m e t a b o l i c demands o f a c t i v i t y . O v e r a one h o u r p e r i o d t h e b r a n c h i a l s o d i u m d e f i c i t ( 1 2 .14 ug/100 g/min.) amounted t o o n l y 31.68 uEq/100 g o r a b o u t l / 2 0 t h o f t h e t o t a l p l a s m a s o d i u m c o n t e n t (600 uEq/100 g ) . The e f f e c t o f t h i s s m a l l l o s s was a p p a r e n t l y n e g a t e d b y a d e c r e a s e i n p l a s m a v o l u m e t h r o u g h a r e d u c t i o n o f w a t e r c o n t e n t , t h e r e b y p r o d u c i n g a s l i g h t augment-a t i o n o f p l a s m a s o d i u m c o n c e n t r a t i o n . However, i f s u c h a n e t b r a n c h i a l e f f l u x r a t e were m a i n t a i n e d d u r i n g p r o l o n g e d swimming, t h e t r o u t w o u l d s o o n s u f f e r o s m o r e g u l a t o r y e m b a r a s s m e n t . A f t e r o n l y 6 - 7 h o u r s , a b o u t 1/3 o f t h e t o t a l p l a s m a s o d i u m w o u l d be l o s t , a s i t u a t i o n o b v i o u s l y d i s a d v a n t a g e o u s t o t h e f i s h . I n a d d i t i o n , t h e swimming a n i m a l ' s p r o b l e m s w o u l d be compounded b y an i n c r e a s e d u r i n a r y s o d i u m l o s s , w h i c h was s u s -p e c t e d a t t h e t i m e t h e s e e x p e r i m e n t s were p e r f o r m e d (Hammond, 1969; H i c k m a n and Trump,1969) a n d c o n f i r m e d b y t h e d a t a o f S e c t i o n I I I . T h u s t h e s o d i u m d e f i c i t , i f u n c h e c k e d , w o u l d 98 c l e a r l y l i m i t t h e d u r a t i o n o f e x e r c i s e t o a m a t t e r o f h o u r s . Y e t t h e r e e x i s t s a g r e a t d e a l o f e v i d e n c e ( s e e B r e t t , 1 9 6 4 ) t h a t f r e s h w a t e r s a l m o n i d s c a n swim a l m o s t i n d e f i n i t e l y a t s u b -f a t i g u e s p e e d s . T h e i n d u c t i o n o f some c o m p e n s a t o r y m e c h a n i s m t o r e d u c e s o d i u m l o s s d u r i n g e x t e n d e d e x e r c i s e was t h e r e f o r e i n d i c a t e d ; t h e e x p e r i m e n t s o f t h i s s e c t i o n were d e s i g n e d t o t e s t t h e v a l i d i t y o f t h i s a s s u m p t i o n . As a c o r r e c t i o n o f t h e n e g a t i v e s o d i u m b a l a n c e c o u l d o c c u r t h r o u g h a m o d i f i c a t i o n o f i n f l u x , e f f l u x o r b o t h p a r a -m e t e r s , i t was a g a i n d e s i r a b l e t o s e p a r a t e t h e u n i d i r e c t i o n a l movements o f t h e i o n b y r a d i o t r a c e r t e c h n i q u e s . The e m p l o y -ment o f t h e s e m e t h o d s o n c e more demanded t h e u s e o f a r e l a t i v e l y s m a l l w a t e r v o l u m e w i t h i t s a t t e n d a n t d i f f i c u l t i e s i n s u p p o r t i n g swimming a c t i v i t y . M a n u a l c h a s i n g was p r e c l u d e d b y t h e e x t e n d e d l e n g t h o f t h e e x e r c i s e p e r i o d s . T h e s e p r o b l e m s were e v e n t u a l l y o v e r c o m e t h r o u g h t h e d e v e l o p m e n t o f a s m a l l r e v o l v -i n g chamber i n w h i c h t r o u t w o u l d swim c o n t i n u o u s l y , a l b e i t a t l o w s p e e d s , f o r many h o u r s . A means f o r d i s t i n g u i s h i n g b e t w e e n b r a n c h i a l and r e n a l c o n t r i b u t i o n t o t h e w h o l e b o d y e f f l u x was a l s o n e c e s s a r y . C o l l e c t i o n o f u r i n e o u t s i d e t h e e x p e r i m e n t a l chamber t h r o u g h an i m p l a n t e d c a t h e t e r as i n S e c t i o n I w o u l d h a v e b e e n t h e most a c c u r a t e s o l u t i o n , b u t was p r e v e n t e d b y t h e u s e o f a c o n s t a n t l y r e v o l v i n g s y s t e m i n w h i c h t h e f i s h r e p e a t e d l y c h a n g e d i t s p o s i t i o n . T h e r e f o r e a more i n d i r e c t a p p r o a c h was t a k e n . S o d i u m f l u x r a t e s were m e a s u r e d d u r i n g l o n g t e r m e x e r c i s e i n b o t h n o r m a l u n e n c u m b e r e d i n d i v i d u a l s and i n a n i m a l s i n w h i c h t h e u r o g e n i t a l p a p i l l a e h a d b e e n o c c l u d e d , t h e r e b y e l i m i n a t i n g t h e r e l e a s e o f u r i n e i n t o t h e e x t e r n a l c o m p a r t m e n t . The d i f f e r e n c e 99 i n mean e f f l u x r a t e s b e t w e e n n o r m a l and l i g a t e d f i s h w o u l d t h u s r e p r e s e n t t h e r e n a l component o f s o d i u m l o s s u n d e r a p a r t i c u l a r c o n d i t i o n . U r i n a r y b l o c k a g e h a s b e e n u s e d p r e v i o u s l y t o e l i m i n a t e r e n a l d i s c h a r g e o f e l e c t r o l y t e s i n s e v e r a l s t u d i e s o f o s m o r e g u l a t i o n i n r a i n b o w t r o u t ( H o l m e s , 1 9 5 9 ; R a n d a l l e_t a_l.,1969) and i n f a c t h a s b e e n r e c e n t l y recommended ( K i r s c h n e r , 1 9 70) a s an a c c e p t a b l e t e c h n i q u e f o r p a r t i t i o n i n g u n i d i r e c t i o n a l f l u x e s i n h y p e r t o n i c r e g u l a t o r s . However none o f t h e s e w o r k e r s h a v e c o n s i d e r e d t h e p o s s i b l e t r a u m a t i c e f f e c t s o f t h i s t r e a t m e n t on t h e a n i m a l , e f f e c t s w h i c h c o u l d d i s t u r b n o r m a l i o n i c b a l a n c e . T h u s a t h i r d g r o u p o f t r o u t (shams) w e r e s u b j e c t e d t o u r i n a r y i n t e r v e n t i o n t o e v a l u a t e t h e i n f l u e n c e o f t h i s p r o c e d u r e a l o n e o n s o d i u m e x c h a n g e s . W e i g h t c h a n g e s o v e r t h e e x p e r i m e n t a l p e r i o d were d e t e r m i n e d on t h e u r i n a r y b l o c k a g e and sham f i s h , a n d t e r m i n a l s a m p l e s f o r d e t e r m i n a t i o n o f h e m a t o c r i t , p l a s m a s o d i u m , a n d p l a s m a and t i s s u e w a t e r c o n -c e n t r a t i o n s were t a k e n f r o m t h e e x p e r i m e n t a l t r o u t . T h e s e m e a s u r e m e n t s were d e s i g n e d t o t e s t w h e t h e r t h e u r i n a r y i n t e r -v e n t i o n a s s o c i a t e d w i t h l i g a t i o n , a n d / o r t h e o c c l u s i o n i t s e l f , p r o d u c e d d i s r u p t i o n s o f i n t e r n a l h o m e o s t a s i s l i k e l y t o d i s t u r b n o r m a l s o d i u m f l u x r a t e s . B e c a u s e o f t h e e x t e n d e d d u r a t i o n o f t h e e x p e r i m e n t s , t h e n e t s o d i u m f l u x e s o f t h e t r o u t i n many c a s e s b r o u g h t a b o u t l a r g e a l t e r a t i o n s o f e x t e r n a l s o d i u m c o n c e n t r a t i o n s ; a m a r k e d c o n c e n t r a t i o n d e p e n d e n c e o f b r a n c h i a l f l u x r a t e s was n o t e d as a r e s u l t o f t h e s e c h a n g e s . The i n f o r m a t i o n p r o v i d e d b y t h e s e o b s e r v a t i o n s h e l d c o n s i d e r a b l e p e r t i n e n c e t o a r g u m e n t s c o n -c e r n i n g t h e m e c h a n i s m s o f b r a n c h i a l s o d i u m e x c h a n g e p r e s e n t e d i n S e c t i o n I. In a d d i t i o n , t h e d a t a *aa»e n o t c o m p l e t e l y c o n s o n -100 a n t w i t h t h e r e s u l t s o f a r e c e n t e x a m i n a t i o n o f t h e c o n c e n -t r a t i o n d e p e n d e n c e o f s o d i u m f l u x e s a c r o s s t h e g i l l s o f a n a e s -t h e t i z e d p e r f u s e d Salmo g a i r d n e r i ( K e r s t e t t e r e t a i l . , 1 9 7 0 ) . . I n l i g h t o f t h e s e f a c t s , t h e r e s u l t s seemed w o r t h y o f a n a l y s i s i n some d e t a i l ; t h e t o p i c h a s b e e n d e a l t w i t h i n P a r t B o f R e s u l t s a n d D i s c u s s i o n i n t h i s S e c t i o n . 101 METHODS I I 1. E x p e r i m e n t a l A n i m a l s A n i m a l s u s e d i n t h i s s t u d y i n c l u d e d b o t h i m m a t u r e a n d s e x u a l l y m a t u r e r a i n b o w t r o u t ( S a l m o g a i r d n e r i ) w e i g h i n g b e t w e e n 160 and 280 g . Some o f t h e f i s h w e r e i n b r e e d i n g c o n d i t i o n . The t r o u t were o b t a i n e d , h e l d , and a c c l i m a t e d as d e s c r i b e d i n S e c t i o n I . D u r i n g t h e a c c l i m a t i o n p e r i o d , t h e f i s h w ere m a i n t a i n e d u n d e r a l m o s t c o n s t a n t i l l u m i n a t i o n t o s u s t a i n t h e d e s i r e d w a t e r t e m p e r a t u r e ( 1 4 . 5 i l . 5 ° C . ) . E x p e r i -m e n t s w e r e p e r f o r m e d d u r i n g December, 1969, a n d J a n u a r y a n d F e b r u a r y , 19 70. 2. O p e r a t i n g P r o c e d u r e s and C a n n u l a t i o n s Two g r o u p s o f t r o u t ( u r i n a r y b l o c k a g e and shams) s t u d i e d i n t h i s s e c t i o n were s u b j e c t e d t o x i r i n a r y c a t h e t e r -i z a t i o n , w h i l e a t h i r d g r o u p ( n o r m a l s ) were n o t h a n d l e d p r i o r t o t h e e x p e r i m e n t . U r i n a r y c a n n u l a e were i m p l a n t e d as i n S e c t i o n I , b u t were c u t o f f a p p r o x i m a t e l y 2 cm p o s t e r i o r t o t h e a n a l f i n . T he c a n n u l a stump was t h e n f i r m l y t i e d t o t h e a n a l f i n w i t h s e v e r a l s i l k s t i t c h e s . O p e r a t e d f i s h w ere a l l o w e d t o r e c o v e r f o r 24 t o 72 h o u r s . 3. E x p e r i m e n t a l S y s t e m S o d i u m i n f l u x , e f f l u x , and n e t f l u x r a t e s w e r e d e t -e r m i n e d h o u r l y f o r t h e 3 t r e a t m e n t g r o u p s on t r o u t p l a c e d i n d i v i d u a l l y i n a r e v o l v i n g swimming chamber f o r 8 h o u r s . S i m u l t a n e o u s r e c o r d s o f t h e f i s h ' s b e h a v i o u r were made, and t e r m i n a l b l o o d and t i s s u e s a m p l e s t a k e n . 102 ( a ) Swimming Chamber The e x e r c i s e chamber c o m p r i s e d a c i r c u l a r p o l y e t h y l e n e b o w l ( d i a m e t e r = 40 cm; d e p t h = 13.5 cm) m o u n t e d on a v a r i a b l e s p e e d m o t o r (kymograph) w h i c h p e r m i t t e d r o t a t i o n a t d i f f e r e n t v e l o c i t i e s ( F i g . 1 6 ) . A h i n g e d p o r t ( d i a m e t e r = 14 cm) t h r o u g h t h e p l e x i g l a s s l i d a l l o w e d a d d i t i o n o f t h e f i s h t o t h e b o w l . C o n t i n u o u s a e r a t i o n was e f f e c t e d b y an a i r s t o n e s u s p e n d e d t h r o u g h t h e c e n t r e o f t h e l i d ; a l e n g t h o f PE 60 t u b i n g a d j a c e n t t o t h e a i r s t o n e p e r m i t t e d p e r i o d i c w a t e r s a m p l i n g . W a t e r t e m p e r a t u r e was d e p e n d e n t on t h e r e l a t i v e l y c o n s t a n t a m b i e n t a i r t e m p e r a t u r e . A v e r a g e e x p e r i m e n t a l t e m p e r a t u r e was 1 5 . 2 ° C . w i t h e x t r e m e s o f 1 3 . 0 ° C . and 1 6 . 5 ° C ; maximum c h a n g e o b s e r v e d d u r i n g an 8 h o u r r u n was 1 . 8 ° C . (b) E x e r c i s e C o n d i t i o n s I n a l l e x p e r i m e n t s , t h e chamber was r o t a t e d a t 20.5 r e v o l u t i o n s / m i n u t e f o r t h e e n t i r e r u n . I n d i v i d u a l t r o u t swam i n o p p o s i t i o n t o t h e c u r r e n t f o r p e r i o d s r a n g i n g f r o m l e s s t h a n 60 m i n u t e s t o t h e f u l l 8 h o u r s . The most r a p i d l y swimming f i s h m a i n t a i n e d t h e i r p o s i t i o n i n t h e chamber r e l a t i v e t o e x t e r n a l c u e s , a n d t h u s a maximum v e l o c i t y o f a b o u t 32 c m / s e c o n d . B e h a v i o u r o f t h e a n i m a l d u r i n g e a c h h o u r p e r i o d was r e c o r d e d as one o f t h r e e w e l l d e f i n e d c a t e g o r i e s : swimming, n o t swimming, o r i n t e r m i t t e n t . The f i r s t two c a t e g o r i e s a r e s e l f - e x p l a n a t o r y ; t h e t h i r d r e f e r s b o t h t o p e r i o d s d u r i n g w h i c h t h e f i s h demon-s t r a t e d i n t e r r u p t e d b o u t s o f a c t i v i t y a n d t o p e r i o d s i n w h i c h t h e t r o u t was swimming a t t h e s t a r t , b u t h a d s t o p p e d b y t h e e n d , o f t h e h o u r . I n a few c a s e s , a " n o t swimming" f i s h w o u l d become a c t i v e a g a i n d u r i n g w a t e r s a m p l i n g , p r o b a b l y i n r e s p o n s e t o o v e r h e a d v i s u a l s t i m u l a t i o n . As t h e s e 103 Figure 16 A drawing of the small volume r e v o l v i n g chamber used for long term exercise of trout i n the experiments of Section I I . 104 swimming b o u t s w e r e e x t r e m e l y s h o r t ( 1 - 2 m i n u t e s ) , a s s i g n -ment t o t h e " n o t swimming" c a t e g o r y r e m a i n e d u n c h a n g e d . ( c ) W e i g h i n g P r o c e d u r e The w e i g h t c h a n g e s o f t h e shams an d u r i n a r y b l o c k a g e t r e a t m e n t g r o u p s o v e r t h e e x p e r i m e n t a l p e r i o d were r e c o r d e d as g r o s s m e a s u r e s o f n e t w a t e r f l u x e s . A t r o u t was r e m o v e d w i t h o u t a n a e s t h e s i a f r o m i t s r e c o v e r y t a n k and p l a c e d i n a b u c k e t o f w a t e r one h o u r b e f o r e t h e s t a r t o f an e x p e r i m e n t . The a n i m a l was t h e n p i c k e d up b y h a n d , s h a k e n b r i e f l y t o remove e x c e s s w a t e r , a n d a d d e d t o a t a r e d p l a s t i c s a c k c o n -t a i n i n g 500 m i s o f w a t e r . The b a g was s t a p l e d c l o s e d a n d w e i g h e d . The t r o u t was t h e n r e t u r n e d t o t h e b u c k e t and t h e p r o c e s s r e p e a t e d . A f t e r c o m p l e t i o n o f t h e w e i g h t d e t e r m i n -a t i o n s , t h e f i s h was p l a c e d b a c k i n i t s a q u a r i u m . An i d e n t -i c a l w e i g h i n g p r o c e d u r e was u s e d on t h e s t u n n e d a n i m a l a t t h e e n d o f t h e e x p e r i m e n t . D u p l i c a t e w e i g h t m e a s u r e m e n t s were a v e r a g e d , a n d t h e c h a n g e o v e r 9 h o u r s e x p r e s s e d i n g/100 g i n i t i a l w e i g h t . I t must be e m p h a s i z e d t h a t t h e p r o c e d u r e , a l t h o u g h a d e q u a t e f o r t h e p u r p o s e s o f t h i s s e c t i o n , was r e l a t i v e l y i n a c c u r a t e due t o v a r i a b l e amounts o f w a t e r a d -h e r i n g t o t h e s u r f a c e o f t h e f i s h ; 5 s u c c e s s i v e d e t e r m i n a t i o n s on a d e a d t r o u t r a n g e d f r o m 2 71.5 g t o 2 73.4 g . However t h o r o u g h d r y i n g o f t h e a n i m a l ( a s i n S e c t i o n I I I ) c o u l d v / e l l h a v e p r o d u c e d u n d e s i r a b l e s t r e s s e f f e c t s on i o n f l u x r a t e s . (d) E x p e r i m e n t a l P r o c e d u r e s and T r e a t m e n t G r o u p s P r i o r t o an e x p e r i m e n t , t h e swimming chamber was f i l l e d w i t h e x a c t l y 6 L o f d e c h l o r i n a t e d f r e s h w a t e r (mean s o d i u m c o n c e n t r a t i o n = 1.61 ug/ml) c o n t a i n i n g 15 - 25 uC o f Na , a n d t h e n s e a l e d w i t h t h e p l e x i g l a s s l i d . 105 ( i ) N o r m a l T r o u t « A f i s h was r e m o v e d d i r e c t l y f r o m t h e a c c l i m a t i o n t a n k and a l l o w e d t o s l i p t h r o u g h wet h a n d s i n t o t h e chamber t h r o u g h t h e p o r t . I t was t h e n g e n e r a l l y n e c e s -s a r y t o w a i t f o r t h e t r o u t t o p o s i t i o n i t s e l f n e a r t h e o u t s i d e o f t h e b o w l i n o p p o s i t i o n t o t h e p r o p o s e d d i r e c t i o n o f r e v o l u t i o n . The chamber was t h e n r o t a t e d s l o w l y a n d t h e d e s i r e d v e l o c i t y a t t a i n e d b y g r a d u a l i n c r e m e n t s i n s p e e d . The d e t a i l s o f t h e p r o c e d u r e v a r i e d w i t h t h e b e h a v i o u r o f t h e i n d i v i d u a l a n i m a l . E x a c t l y 10 m i n u t e s a f t e r a d d i t i o n o f t h e f i s h t o t h e b o w l , a w a t e r s a m p l e (10 ml) was drawn; f u r t h e r w a t e r s a m p l e s were t a k e n a t 60 m i n u t e i n t e r v a l s f o r 8 h o u r s 22 t o m e a s u r e t h e d e c l i n e o f Na a n d t h e c h a n g e i n t o t a l s o d i u m c o n c e n t r a t i o n o f t h e e x t e r n a l medium. W a t e r r a d i o a c t i v i t y d e c r e a s e d a p p r o x i m a t e l y 8 5 % d u r i n g t h e e x p e r i m e n t a l p e r i o d . O b s e r v a t i o n s o f t h e f i s h ' s b e h a v i o u r w e r e made t w i c e an h o u r as d e s c r i b e d a b o v e . A f t e r 8 h o u r s , t h e t r o u t was q u i c k l y r e m o v e d f r o m t h e chamber, s t u n n e d b y a b l o w on t h e h e a d , r i n s e d w i t h f r e s h w a t e r , and d r i e d w i t h p a p e r t o w e l s . A b l o o d s a m p l e (500 u l ) was drawn b y c a r d i a c p u n c t u r e i n t o a h e p a r i n i z e d s y r i n g e a n d c e n t r i f u g e d i m m e d i a t e l y ; t i s s u e s a m p l i n g , w e i g h i n g , a n d m e a s u r i n g p r o c e d u r e s were p e r f o r m e d a s i n S e c t i o n I . ( i i ) U r i n a r y B l o c k a g e T r o u t . A f t e r t h e w e i g h t d e t e r -m i n a t i o n s , a s t a i n l e s s s t e e l p i n was i n s e r t e d i n t o t h e stump o f t h e u r i n a r y c a n n u l a , a n d t h e f i s h r e t u r n e d t o a r e c o v e r y a q u a r i u m . E x a c t l y one h o u r l a t e r , t h e t r o u t was t r a n s f e r r e d t o t h e swimming chamber an d t h e e x p e r i m e n t a l p r o t o c o l f o l l o w e d a s f o r t h e n o r m a l g r o u p . A t t h e e n d o f t h e e x p e r i m e n t , t h e f i s h was a g a i n w e i g h e d t w i c e b e f o r e b l o o d a n d t i s s u e s a m p l i n g . 106 P a t e n c y o f t h e u r i n a r y c a n n u l a was c h e c k e d b y i n j e c t i o n o f d y e d s a l i n e . O f t h e 17 f i s h s u b j e c t e d t o u r i n a r y b l o c k a g e , h y d r o s t a t i c p r e s s u r e r e s u l t i n g f r o m t h e b u i l d - u p o f u r i n e h a d c a u s e d r u p t u r e o f t h e u r o g e n i t a l p a p i l l a i n 8. A l l d a t a f r o m t h e s e t r o u t w e r e d i s c a r d e d . ( i i i ) Sham T r o u t . T h e s e a n i m a l s were s u b j e c t e d t o t h e same e x p e r i m e n t a l r e g i m e as t h e u r i n a r y b l o c k a g e g r o u p . How-e v e r , t h e p r o c e d u r e o f p l u g g i n g t h e u r i n a r y c a n n u l a was m e r e l y m i m i c k e d t h r o u g h s e v e r a l f i r m t u g s on t h e t u b i n g ; t h e c a t h e t e r was c h e c k e d p o s t - e x p e r i m e n t a l l y t o e n s u r e t h a t i t h a d r e m a i n e d f r e e - d r a i n i n g . 4. A n a l y t i c a l P r o c e d u r e s D e t e r m i n a t i o n s o f t e r m i n a l h e m a t o c r i t , p l a s m a a n d t i s s u e w a t e r , p l a s m a a n d w a t e r s o d i u m , a n d w a t e r r a d i o a c t i v i t y w ere p e r f o r m e d a s i n S e c t i o n I . A l l f l a m e e m i s s i o n a n a l y s e s were done on t h e T e c h t r o n M o d e l AA 120 A t o m i c A b s o r p t i o n 22 S p e c t r o p h o t o m e t e r ( s e e S e c t i o n I ) . Na i n t e r m i n a l p l a s m a was a s s a y e d on d u p l i c a t e 25 uL a l i q u o t s w h i c h h a d b e e n d i l u t e d t o 1 ml w i t h w a t e r a n d d r i e d u n d e r a h e a t l a m p . 5. C a l c u l a t i o n s (a) S o d i u m F l u x R a t e s The m e t h o d d e s c r i b e d i n S e c t i o n I f o r c a l c u l a t i o n o f f l u x r a t e s i s c o m p l i c a t e d i n l o n g t e r m e x p e r i m e n t s b y t h e 22 r e t u r n o f t h e l a b e l l e d i s o t o p e Na f r o m t h e f i s h t o t h e w a t e r . I n t h e p r e s e n t s t u d y , t h e i n t e r n a l s p e c i f i c a c t i v i t y o f s o d i u m a p p r o a c h e d 35% o f t h e e x t e r n a l s p e c i f i c a c t i v i t y a f t e r 8 h o u r s . C o m p u t a t i o n o f i n f l u x r a t e w i t h o u t c o m p e n s a t i o n f o r b a c k f l u x o f t h e r a d i o i s o t o p e w o u l d y i e l d a v a l u e i n f e r i o r t o t h e t r u e 107 i n f l u x r a t e . T h u s i t was n e c e s s a r y t o u t i l i z e t h e e q u a t i o n o f M a e t z (1956) t o d e t e r m i n e i o n i n f l u x r a t e s i n f r e s h w a t e r d u r i n g l o n g t e r m e x p e r i m e n t s . The f o l l o w i n g d e s c r i p t i o n o f t h e t h e o r e t i c a l d e r i v a t i o n o f t h i s e q u a t i o n h a s b e e n m o d i f i e d f r o m M a e t z ( 1 9 5 6 ) . The a n a l y s i s i s b a s e d o n t h e a s s u m p t i o n t h a t t h e f i s h ( i n t e r n a l ) and t h e w a t e r ( e x t e r n a l ) r e p r e s e n t a two c o m p a r t m e n t s y s t e m b e t w e e n w h i c h a l l i o n movements o c c u r . S y m b o l s : Na e x t Na i n t Qo Q Q f At 22 T o t a l q u a n t i t y o f s o d i u m ( u g ) c o n t a i n e d i n t h e e x t e r n a l w a t e r a t a p a r t i c u l a r t i m e t . Q u a n t i t y o f e x c h a n g e a b l e s o d i u m ( u g ) c o n t a i n e d i n t h e f i s h a t t . 22 T o t a l q u a n t i t y o f Na (c.p.m.) a d d e d t o t h e e x t e r n a l w a t e r a t t i m e z e r o . 22 T o t a l q u a n t i t y o f Na (c.p.m.) r e m a i n i n g i n t h e e x t e r n a l w a t e r a t t . 2 2 T o t a l q u a n t i t y o f Na (c.p.m.) r e m a i n i n g i n t h e e x t e r n a l w a t e r a t t h e e n d o f t h e e x p e r i m e n t (8 h r s ) . T i m e p e r i o d o v e r w h i c h t h e i n f l u x r a t e i s m e a s u r e d (60 m i n u t e s ) . 22 Na /ml p f : C o n c e n t r a t i o n o f Na i n a t e r m i n a l p l a s m a s a m p l e ( c . p . m . / m l ) . Na/ml p f : C o n c e n t r a t i o n o f s o d i u m i n a t e r m i n a l p l a s m a s a m p l e ( u g / m l ) . F i : Na i n f l u x r a t e ( u g / m i n u t e ) . Fo : Na e f f l u x r a t e ( u g / m i n u t e ) . Fn : Na n e t f l u x r a t e ( u g / m i n u t e ) . A t t i m e t t h e s p e c i f i c a c t i v i t y o f s o d i u m i n t h e e x t e r n a l com-p a r t m e n t i s Q , w h i l e t h a t o f t h e i n t e r n a l c o m p a r t m e n t i s Na e x t 22 Qo - Q. T h u s o v e r A t , t h e amount o f Na e n t e r i n g t h e i n t e r -Na i n t n a l c o m p a r t m e n t may be e x p r e s s e d : F i x Q x A t (1) Na e x t 108 22 C o n v e r s e l y , t h e amount o f Na l e a v i n g t h e i n t e r n a l c o m p a r t -ment i s : Fo x (Qo - Q) x A t (2) Na i n t 22 T h u s t h e c h a n g e i n t o t a l e x t e r n a l Na (AQ) o v e r A t i s g i v e n b y t h e d i f f e r e n c e b e t w e e n e x p r e s s i o n s (1) a n d ( 2 ) : A Q = I - Q x F i x A t | + ] ( Q o - Q ) x F o x A t t | + M Qo - Q : _J [_ Na i n t •I (3) Na e x t I n f r e s h w a t e r t e l e o s t s , F i r a r e l y e q u a l s F o , a n d t h u s Fn d o e s n o t u s u a l l y e q u a l z e r o o v e r t h e t i m e i n t e r v a l o f an-ex-p e r i m e n t . C o n s e q u e n t l y , Na e x t v a r i e s w i t h t i m e i n a n o n -l i n e a r f a s h i o n , p r e v e n t i n g i n t e g r a t i o n o f e q u a t i o n ( 3 ) . I t i s t h e r e f o r e n e c e s s a r y t o c a l c u l a t e f l u x e s b y n u m e r i c a l r e s o l u t i o n o v e r e a c h t i m e i n t e r v a l . The n e t f l u x i s c o n -s i d e r e d p o s i t i v e when t h e amount o f s o d i u m i n t h e e x t e r n a l c o m p a r t m e n t d i m i n i s h e s : Fn = - ANa e x t At a n d r e p r e s e n t s t h e d i f f e r e n c e b e t w e e n F i and Fo Fn = F i — Fo S o l u t i o n o f e q u a t i o n (4) a n d (5) f o r Fo a n d s u b s t i t u t i o n o f t h i s t e r m i n (3) p r o d u c e s t h e f o l l o w i n g e q u a t i o n : AQ = At| -Q x F i + Qo - Q x ( F i + 4 Na e x t ) Na e x t Na i n t A t (4) (5) a n d b y s o l u t i o n f o r F i — - — AQ - Qo - Q 4 N a e x t A t Na i n t A t _ Qo - Q Q Na i n t Na e x t (6) (7) Fo may t h e n be d e d u c e d f r o m e q u a t i o n ( 5 ) . I t i s i n t e r e s t i n g t o n o t e t h a t d u r i n g a s h o r t t e r m e x p e r i m e n t , t h e q u a n t i t y (Qo - Q) i s n e g l i g i b l e , a n d e q u a t i o n s i m p l i f i e s t o : 109 A2, F i = - At (8) Q Na e x t w h i c h i s t h e r e l a t i o n s h i p u s e d t o c a l c u l a t e F i i n S e c t i o n I . A l l t e r m s i n e q u a t i o n (7) w i t h t h e e x c e p t i o n o f Na i n t , a r e 22 r e a d i l y e x t r a c t a b l e f r o m d a t a on c h a n g e s i n s o d i u m a n d Na c o n c e n t r a t i o n s i n t h e w a t e r . As Fn v a r i e s d u r i n g t h e e x p e r i -ment, Na i n t must v a r y t o m i r r o r c h a n g e s i n Na e x t . However, s i n c e Na i n t i s l a r g e r e l a t i v e t o Na e x t , t h e s e s l i g h t d e v -i a t i o n s may be i g n o r e d , and Na i n t may be a p p r o x i m a t e d f r o m t h e t e r m i n a l p l a s m a s a m p l e : Qo - Qf Na i n t X T 22 , .. _ (9) Na /ml p f /ml p f 22 (b) Na S p a c e The d i s t r i b u t i o n v o l u m e o f r a d i o s o d i u m ( V i n t ) was 22 c a l c u l a t e d a s i n S e c t i o n I f r o m t h e t o t a l mount o f Na i n . t h e f i s h a f t e r 8 h o u r s a n d t h e r a d i o a c t i v i t y o f t h e t e r m i n a l p l a s m a s a m p l e : V i n t = Qo - Q f (10) 22 Na /ml p f 110 RESULTS AND DISCUSSION II A. Sodium Flux Rates during Extended Exercise The r e s u l t s of t h i s s e c t i o n were obtained from a completely d i f f e r e n t set of rainbows from those used i n Section I; t h e i r p h y s i c a l dimensions are presented i n Table IX. The animals were generally smaller and thinner (as manifested by the low c o e f f i c i e n t s of condition) than the f i r s t group ( c f . Table II) and many were i n prime breeding condition. These batch d i f f e r e n c e s probably accounted for the s l i g h t l y higher sodium i n f l u x rates and plasma concentrations observed i n the present study. However Table IX demonstrates that body weights and c o e f f i c i e n t s of condition did not vary s i g n i f i c -antly among the three experimental groups of t h i s section, thereby again allowing comparison of f l u x rates between t r e a t -ments on a per 100 g body weight b a s i s . It was the object of t h i s i n v e s t i g a t i o n to measure on a temporal basis any progressive changes which occurred i n fl u x components i n response to long term swimming. Inter-p r e t a t i o n of the r e s u l t s was however complicated by several f a c t o r s . Flux rate values from a t y p i c a l experiment have been g r a p h i c a l l y presented i n F i g . 17 to i l l u s t r a t e the d i f f i -c u l t i e s encountered i n evaluation of data and the method of analysis applied. Indivi d u a l trout exhibited v a r i a b l e behaviour i n the exercise chamber, swimming for periods ranging from l e s s than one hour to the e n t i r e eight hours of the experi-ment. C l a s s i f i c a t i o n of a p a r t i c u l a r hourly flux rate value was therefore dependent not only on whether the animal was I l l T a b l e IX. P h y s i c a l dimensions o f t r o u t i n the t h r e e t r e a t m e n t groups o f S e c t i o n I I . Means - 1 s t a n d a r d e r r o r Normal Sham U r i n a r y Blockage N = 10 N = 10 N ° 9 Body weight (g) 186.92 - 5.42 190.60 - 10.19 180.09 - 6.95 Length (cm) 28.84 - 0.40 28.73 - 0.57 28.42 - 0.35 Fork l e n g t h 27.70 - 0.39 27.38 ± 0.49 27.26 - 0.33 (cm) Max.depth 5.50 i .08 5.52 - .08 5.65 - .11 (cm) C o e f f i c i e n t 0.882 - .026 0.928 ± .036 0.889 - .036 o f c o n d i t i o n weight x IQO3 ( f o r k l e n g t h ) No s i g n i f i c a n t d i f f e r e n c e s between c o r r e s p o n d i n g v a l u e s i n d i f f e r e n t groups 112 Figure 17 Results of a t y p i c a l experiment of Section II i l l u s t r a t i n g the method of data analysis applied. Black bars = sodium i n f l u x r a t e s ; dotted bars = sodium e f f l u x r a t e s ; c l e a r bars = sodium net f l u x r a t e s . Below approximately 0.8 ug Na +/ml, i n f l u x rare became dependent on external sodium concen-t r a t i o n . Fish 4 5 - S h a m ,180.6 g. £ 150 I - L ioo E £ u) Q50 x o L U ( J i £ D O C O 0.00 •50.0 •40.0 •30.0 •20.0 •10.0 0.0 -10.0 -20.0 -30.0 -40.0 a Swimming Behavior s w i m - s w , m -Classification ]st 2 n <^ hour hour swim. 0 swim. inter. inter. inter. inter. inter. n Q * swim. inter. hour recov. DJ not swim. not swim. 2nd hour recov. subse-quent hours recov. Time (hours) 8 swimming o r not, but on the l e n g t h o f time p r i o r t o the measurement p e r i o d d u r i n g which the animal had been a c t i v e o r r e s t i n g . I n s p e c t i o n o f d a t a from experiments i n which the t r o u t had swum f o r most o r a l l o f the e i g h t hours r e v e a l e d no marked v a r i a t i o n i n sodium movements a f t e r the f i r s t t h r e e hours o f e x e r c i s e . S i m i l a r l y , f l u x r a t e s o f f i s h which spent most o f t h e i r time at r e s t had s t a b i l i z e d by t h r e e hours a f t e r t h e c e s s a t i o n o f swimming. F i g . 18 p r e s e n t s c h a r a c t e r i s t i c examples o f t h e s e c a s e s . C o n s e q u e n t l y , h o u r l y d e t e r m i n a t i o n s were d i v i d e d i n t o the f o l l o w i n g s e l f - e x p l a n a t o r y c a t e g o r i e s : f i r s t hour swimming, second hour swimming, subsequent hours swimming, i n t e r m i t t e n t , f i r s t hour re c o v e r y , second hour r e c o v e r y , and subsequent hours r e c o v e r y . The c l a s s i f i c a t i o n p r o c e d u r e i s i l l u s t r a t e d by the experiment o u t l i n e d i n F i g . 17. A l l the v a l u e s o f a f l u x component f o r a p a r t i c u l a r c a t e g o r y from e v e r y animal i n the treatment group were then averaged. Each h o u r l y measurement was t h e r e f o r e weighted e q u a l l y i n the mean a l t h o u g h some f i s h o b v i o u s l y c o n t r i b u t e d more v a l u e s t o a p a r t i c u l a r c a t e g o r y than d i d o t h e r s . A f u r t h e r problem i n d a t a a n a l y s i s e v o l v e d from the l a r g e d i m i n u t i o n s i n e x t e r -n a l sodium c o n c e n t r a t i o n caused by the h i g h l y p o s i t i v e net f l u x r a t e s o f some t r o u t ; the e f f e c t was e s p e c i a l l y p r e v a l e n t i n the u r i n a r y b l o c k a g e group which s u f f e r e d no r e n a l e f f l u x . In a l l groups, t h e r e o c c u r r e d a marked d e p r e s s i o n o f b r a n c h i a l i n f l u x r a t e at low sodium l e v e l s o f the o u t s i d e water. I n -v e s t i g a t i o n o f the i n t e r a c t i o n between sodium c o n c e n t r a t i o n and i n f l u x r a t e r e v e a l e d t h a t a t average e x t e r n a l sodium l e v e l s g r e a t e r t h a t 0.8 ug/ml, the s l o p e o f the r e g r e s s i o n l i n e o f i n f l u x on c o n c e n t r a t i o n d i d not d i f f e r s i g n i f i c a n t l y from 114 Figure 18 Results of two experiments of Section I I . Black bars = sodium i n f l u x r a t e s ; dotted bars = sodium e f f l u x r a t e s ; c l e a r bars = sodium net fl u x r a t e s . Upper: Example of an animal which swam continuously for 8 hours. Sodium f l u x rates had s t a b i l i z e d by the t h i r d hour of exer c i s e . Lower": Example of an animal which was i n a c t i v e for most of the experimental period. Sodium f l u x rates had s t a b i l i z e d by the t h i r d hour a f t e r termination of exercise. c J CO 0) O or x E D O CO Fish 30 Sham, 181.8g. +50.0--40.0 +30.0 +20.0--10.0 0.0 -10.0 -20.0 -30.0 -40.0 -50.0 -60.0 (8162) 0 D SWIM MING-a fffs p n n n Time (hours) 8 c E «/> 0 O cr X ' 3 E 2 O CO Fish25 Normal,209.8g. +50.0 +40.0 + 30.0 +20.0 +10.0 0.0 -10.0 -20.0 -30.0--40.0 -50.0 -60.0 SWIM. ?3£ D 0 INTER. | +- NOT a SWIMMI NG m a 51 n n n 2 3 4 5 Time (hours) 8 115 zero, whereas below t h i s f i g u r e , there existed a d e f i n i t e p o s i t i v e c o r r e l a t i o n . In Part B of t h i s s e c t i o n , i t has been shown that the data agrees well with a t y p i c a l M i c h a e l i s -Menten curve ( c f . F i g . 20) which tends to approach the zero-order r e l a t i o n s h i p a f t e r 0.8 ug/ml. Comparison of i n f l u x rate means between and within groups was therefore v a l i d only i f a l l the components of the averages had been determined over that part of the curve where "substrate" concentration had l i t t l e e f f e c t on " v e l o c i t y " . A s i m i l a r argument must apply to net f l u x r a t e s , and to e f f l u x rates i f the l a t t e r are d i r e c t l y (exchange d i f f u s i o n ) or i n d i r e c t l y (back-transport) l i n k e d to i n f l u x r a t e s . Thus i t was necessary to d i s c a r d from the means a l l f l u x measurements taken at average external sodium concentrations l e s s than 0.8 ug/ml. ( F i g . 17). F i g . 19 d i s p l a y s the r e s u l t s of the above analysis for the three treatment groups. Sodium e f f l u x rates ( F i g . 19) were s l i g h t l y higher i n the shams and thus net movements marginally l e s s p o s i t i v e r e l a t i v e to the normals, but the d i f f e r e n c e s were generally not large enough to obtain s t a t i s t i c a l v a l i d a t i o n . These two sets of trout demonstrated extremely s i m i l a r trends of f l u x rate v a r i a t i o n i n response to the state of exercise. Dis-regarding for the present the data from the urinary blockage f i s h , a number of conclusions may be drawn from the sodium exchanges of these two groups. F i r s t l y , b r anchial sodium i n f l u x rate exhibited remarkable s t a b i l i t y over the experi- ' mental period. The only s t a t i s t i c a l l y s i g n i f i c a n t d i v e r -gence i n t h i s parameter occurred between 1st hour swimming and 2nd hour recovery values i n the normals, and between the 116 Figure 19 Sodium fl u x r a t e s , measured at external concentrations greater than 0.8 ug/ml, under d i f f e r e n t exercise con-d i t i o n s i n normal (10), sham (10), and urinary blockage (9) t r o u t . Black bars = sodium i n f l u x rates; dotted bars = sodium e f f l u x rates; c l e a r bars = sodium net flu x r a t e s . V e r t i c a l l i n e s represent 1 standard error of each mean. Each average includes a l l acceptable data i n the category; thus i t was possib l e f o r a s i n g l e f i s h to contribute more than one value to the mean i n c l a s s -i f i c a t i o n s 3, 4, and 7. S t a t i s t i c a l Comparisons: (Numbers r e f e r to means of exer-c i s e conditions as l a b e l l e d at the head of the graph.) Normal: Influx Rate. F = 1.59, n.s. 6 5 7 4 3 2 1 E f f l u x Rate. F = 13.90, p<.005 6 7 5 3 4 2 1 Net Flux Rate. F = 4.59, p< .005 1 2 4 5 3 7 6 Sham: Influx Rate. F = 1.61, n.s. 4 5 6 2 3 1 7 E f f l u x Rate. F = 5.63, p<.005 6 4 5 3 7 2 1 Net Flux Rate. F = 6.62, p<.005 1 2 4 3 5 7 6 Urinary Blockage:Influx Rate. F = 1.94, n.s. 7 6 5 4 2 1 E f f l u x Rate. F = 0.20, n.s. 5 2 7 1 6 4 Net Flux Rate. F = 1.52, n.s. 7 6 4 5 2 1 A = s i g n i f i c a n t l y d i f f e r e n t from corresponding normal value (p < .05) B = s i g n i f i c a n t l y d i f f e r e n t from corresponding sham value (p < .05) C = s i g n i f i c a n t l y d i f f e r e n t from both normal and sham values (p < .05) — = not s i g n i f i c a n t l y d i f f e r e n t from other corresponding values (p y .05) CO g + 3 C + "5+20 in +10 0 < OS g -1C+ -20f |-3C+ O C O +30 +20 + 10 0 -10 -20 -30 1 1 s t Hour Swimming n=9 n=10 I? n = 9 lbs; _ c c 2 2"dHour Swimming n=4 r n=8 . 1 f n = 3 _ C B 3 Subsequent Hours Swimming n=11 M n=16 No Dato Intermittent n=12 1-1 r n=!5 n=9 • i i — A A 5 1 s t Hour Recovery n=7 n = 6 n=5 n B C 6 2ndHour Recovery n=6 2 a n=6 .3 i a n=4 1 a 7 Subsequent Hours Recovery n=20 NORMAL a n=14 SHAM A A n=4 URINARY BLOCKAGE B i n t e r m i t t e n t a n d s u b s e q u e n t h o u r s r e c o v e r y f i g u r e s o f t h e shams. As t h e s e d i f f e r e n c e s a t t a i n e d o n l y b o r d e r l i n e s t a t -i s t i c a l c o n f i r m a t i o n ^ w e r e n o t c o n s i s t e n t b e t w e e n t h e two 1 t r e a t m e n t s , and were n o t c o n c o r d a n t w i t h any g e n e r a l t r e n d s i n t h e d a t a , i t seems d o u b t f u l t h a t t h e y r e p r e s e n t e d any m e a n i n g f u l v a r i a t i o n . An a u g m e n t a t i o n o f s p u r i o u s s t a t i s t -i c a l e f f e c t s i s u n f o r t u n a t e l y c o n c o m i t a n t w i t h t h e u n e q u a l c o n t r i b u t i o n o f d a t a f r o m s i n g l e s o u r c e s t o t h e mean. Th e i n s e n s i t i v i t y o f b r a n c h i a l s o d i u m i n f l u x r a t e t o f a c t o r s a s s o c -i a t e d w i t h s h o r t t e r m e x e r c i s e a n d r e c o v e r y ( o n e h o u r ) was e s t a b l i s h e d i n S e c t i o n I . T h i s c o n c l u s i o n may now be e x t e n d e d t o p r o l o n g e d swimming, a t l e a s t a t l o w v e l o c i t y , a n d t h e s u b s e q u e n t r e c o v e r y p e r i o d f o l l o w i n g s u c h e x e r c i s e . S o d i u m e f f l u x r a t e ( F i g . 19) was, h o w e v e r , v u l n e r -a b l e t o t h e i n f l u e n c e o f t h e p r e v a i l i n g e x e r c i s e c o n d i t i o n . U n i d i r e c t i o n a l out \v-ard movements were g r e a t e s t d u r i n g t h e f i r s t h o u r o f swimming b u t d e c l i n e d s i g n i f i c a n t l y t o p o s t - e x e r c i s e l e v e l s b y t h e t h i r d a n d s u b s e q u e n t h o u r s o f a c t i v i t y . V a r i -a t i o n s i n n e t f l u x r a t e s f o l l o w e d a s i m i l a r p a t t e r n . The h y p o t h e s i s w h i c h t h e s e e x p e r i m e n t s were d e s i g n e d t o t e s t , n a m e l y t h a t t h e t r o u t i s a b l e t o o v e r c o m e t h e n e t s o d i u m d e f i c i t a s s o c i a t e d w i t h s h o r t p e r i o d s o f swimming t h r o u g h t h e i m p l e m -e n t a t i o n o f c o m p e n s a t o r y m e c h a n i s m s d u r i n g p r o l o n g e d e x e r c i s e , was t h e r e f o r e c o n f i r m e d . T h i s a d a p t a t i o n a p p a r e n t l y o c c u r r e d e n t i r e l y t h r o u g h r e d u c t i o n o f t h e e f f l u x r a t e , t h e same f a c t o r whose e l e v a t i o n was o r i g i n a l l y r e s p o n s i b l e f o r t h e n e g a t i v e b a l a n c e s i t u a t i o n o v e r t h e i n i t i a l e x e r c i s e i n t e r v a l . The s o d i u m e x c h a n g e d a t a o f t r o u t #30 ( F i g . 18) w h i c h swam c o n t i n -u o u s l y t h r o u g h o u t t h e 8 h o u r s , p r o v i d e e x c e l l e n t i l l u s t r a t i o n 118 o f t h i s phenomenon; s o d i u m e f f l u x was e x t r e m e l y h i g h d u r i n g t h e f i r s t h o u r o f m e a s u r e m e n t p r o d u c i n g a p r o n o u n c e d n e t l o s s o f t h e e l e c t r o l y t e t o e n v i r o n m e n t . T h i s d e f i c i t p e r s i s t e d o v e r t h e s e c o n d h o u r d e s p i t e a l a r g e r e d u c t i o n i n t h e o u t w a r d m o v i n g c o m p o n e n t . By t h e t h i r d h o u r , f i s h #30 h a d r e t u r n e d t o a p o s i t i v e b a l a n c e s i t u a t i o n w h i c h was m a i n t a i n e d t h r o u g h o u t t h e f o l l o w i n g f i v e h o u r s o f e x e r c i s e . I t may be n o t e d i n F i g . 19 t h a t a t l e a s t f o r t h e n o r m a l g r o u p , t h e e f f l u x r a t e o f t h e i n t e r m i t t e n t c a t e g o r y was g r e a t e r t h a n t h a t o f s u b s e q u e n t h o u r s swimming, a d i f f e r -e n c e w h i c h was r e f l e c t e d b y t h e r e t u r n o f t h e n e x t f l u x t o a n e g a t i v e v a l u e . T h i s e f f e c t was p r o b a b l y e x p l a i n a b l e b y t h e b e h a v i o u r o f t r o u t i n t h e i n t e r m i t t e n t c a t e g o r y , w h i c h c o n s i s t e d o f s h o r t r a p i d b u r s t s o f swimming i n t o t h e c u r r e n t f o l l o w e d b y i n t e r v a l s o f r e s t . S u c h a c t i v i t y p r o d u c e s l a r g e i n c r e a s e s i n o x y g e n u p t a k e ( B r e t t , 1 9 6 4 ) , w h i c h , c o m b i n e d w i t h p o s s i b l e d i s r u p t i o n o f t h e c o m p e n s a t o r y phenomenon t h r o u g h t h e i r r e g u l a r n a t u r e o f t h e a c t i v i t y , c o u l d h a v e b e e n r e s p o n s i b l e f o r an i n c r e a s e i n t h e e f f l u x e l e m e n t . B o t h g r o u p s e x h i b i t e d a minimum e f f l u x v a l u e d u r i n g t h e s e c o n d h o u r o f r e c o v e r y ( F i g . 19) a c c o m p a n i e d b y a maximum p o s i t i v e n e t f l u x . S u b s e q u e n t h o u r s o f r e c o v e r y were c h a r a c t e r i z e d b y a r e t u r n t o a s l i g h t l y g r e a t e r e f f l u x a s s o c i a t e d w i t h a somewhat l o w e r n e t s o d i u m u p t a k e . A s i m i l a r i n c r e a s e i n n e t f l u x t h r o u g h r e d u c t i o n o f t h e b r a n c h i a l e f f l u x p a r a m e t e r d u r i n g r e c o v e r y was o b s e r v e d i n t h e e x p e r i m e n t s o f S e c t i o n I . I t must be e m p h a s i z e d t h a t t h e s o d i u m e f f l u x r a t e s d i s c u s s e d a b o v e were w h o l e o r g a n i s m m e a s u r e m e n t s f o r t h e n o r m a l s a n d shams and t h u s r e p r e s e n t e d t h e sum o f b r a n c h i a l a n d r e n a l c o n t r i b u t i o n s . T h e e x p e r i m e n t s w i t h u r i n a r y o c c l u d e d r a i n b o w s were p e r f o r m e d i n o r d e r t o a s c e r t a i n t h e r o l e o f e a c h c o n s t i t u e n t i n t h e o b s e r v e d r e s p o n s e s . R e j e c t i o n o f many f l u x r a t e d e t e r m i n a t i o n s f r o m t h e l i g a t e d f i s h was u n f o r t u n a t e l y n e c e s s i t a t e d b y t h e 0.8 ug/ml e x t e r n a l s o d i u m l e v e l c r i t e r i o n . T h e a c c e p t a b l e d a t a , w i t h one e x c e p t i o n , h o w e v e r , was w e l l d i s t r i b u t e d b e t w e e n d i f f e r e n t e x p e r i m e n t s a n d e x h i b i t e d o n l y m o d e r a t e v a r i a b i l i t y . On t h i s b a s i s , one may h a v e some c o n -f i d e n c e i n t h e r e p r e s e n t a t i v e n a t u r e o f t h e means c a l c u l a t e d f r o m t h e r e m a i n i n g m e a s u r e m e n t s ( F i g . 1 9 ) . B r a n c h i a l i n f l u x r a t e s o f l i g a t e d t r o u t showed no s i g n i f i c a n t v a r i a t i o n w i t h r e s p e c t t o e i t h e r d i f f e r e n t e x e r c i s e c o n d i t i o n s w i t h i n t h e t r e a t m e n t g r o u p , o r c o m p a r a b l e means o f t h e o t h e r two s e t s o f f i s h , w i t h t h e e x c e p t i o n o f t h e s u b -s e q u e n t h o u r s r e c o v e r y v a l u e . T h i s l o n e a n o m a l y , w h i c h was a l s o t r u e o f n e t f l u x r a t e , c a n be a s c r i b e d t o t h e f a c t t h a t t h r e e o f t h e f o u r v a l u e s i n t h e a v e r a g e came f r o m a s i n g l e a n i m a l w h i c h d e m o n s t r a t e d c h a r a c t e r i s t i c a l l y l o w i n f l u x r a t e s t h r o u g h o u t t h e e x p e r i m e n t . T h u s t h e i n w a r d movement o f s o d i u m a c r o s s t h e g i l l e p i t h e l i u m o f u r i n a r y b l o c k a g e a n i m a l s showed s i m i l a r m a g n i t u d e a n d s t a b i l i t y t o t h a t o f t h e u n l i g a t e d f i s h . S o d i u m e f f l u x r a t e s o f t h e o c c l u d e d t r o u t w e r e i n mo s t c a s e s s i g n i f i c a n t l y l o w e r t h a n t h e c o r r e s p o n d i n g v a l u e s f o r e i t h e r o r b o t h o f t h e o t h e r two t r e a t m e n t s , b u t r e m a i n e d e x t r e m e l y c o n s t a n t u n d e r d i f f e r e n t a c t i v i t y c o n d i t i o n s . I f t h e a s s u m p t i o n i s t a k e n t h a t b r a n c h i a l s o d i u m e f f l u x , l i k e i n f l u x , was u n a f f e c t e d b y u r i n a r y o c c l u s i o n , t h e n t h e o b s e r v e d c h a n g e s i n w h o l e b o d y u n i d i r e c t i o n a l l o s s e s d u r i n g p r o l o n g e d 120 swimming must be a t t r i b u t e d t o v a r i a t i o n i n t h e r e n a l e f f l u x c o m p o nent a l o n e . On t h i s b a s i s , t h e u r i n a r y e x c r e t i o n o f s o d i u m u n d e r d i f f e r e n t c o n d i t i o n s c o u l d b e a p p r o x i m a t e d b y s u b -t r a c t i o n o f u r i n a r y b l o c k a g e s o d i u m e f f l u x means f r o m sham e f f l u x means. T a b l e X p r e s e n t s t h e r e s u l t s o f t h i s c a l c u l -a t i o n . T h e s e e s t i m a t e s i n d i c a t e t h a t t h e r e n a l d i s c h a r g e o f s o d i u m was h i g h d u r i n g t h e f i r s t h o u r o f e x e r c i s e b u t h a d d e c r e a s e d t o r e c o v e r y l e v e l s b y t h e t h i r d a n d s u b s e q u e n t h o u r s o f swimming. T h e s e c o n c l u s i o n s s e r i o u s l y d i s a g r e e w i t h t h e r e s u l t s o f S e c t i o n I w h i c h d e m o n s t r a t e d a v e r y s i g n i f i c a n t a u g m e n t a t i o n o f t h e r a t e o f s o d i u m e f f l u x a c r o s s t h e g i l l s d u r i n g e x e r c i s e . T h i s d i s c r e p a n c y c o u l d b e e x p l a i n e d i f t h e b r a n c h i a l s o d i u m e f f l u x e s o f u r i n a r y o c c l u d e d r a i n b o w s were n o t r e p r e s e n t a t i v e o f r a t e s i n t h e n o r m a l s and shams; i . e . i f t h e e f f l u x v a r i a t i o n s o f t h e s e two g r o u p s d i d i n f a c t i n c l u d e a s i g n i f i c a n t b r a n c h i a l c o m p o nent w h i c h was n o t e v i d e n t i n t h e l i g a t e d i n d i v i d u a l s . A n a s s e s s m e n t o f t h e v a l i d i t y o f t h e c a l c u l a t e d r e n a l e f f l u x r a t e s ( T a b l e X) p r o v i d e s c o g e n t s u p p o r t f o r t h i s h y p o t h e s i s . I n S e c t i o n I I I , u r i n a r y s o d i u m o u t p u t s were m e a s u r e d d i r e c t l y t h r o u g h c o l l e c t i o n a n d a n a l y s i s o f t h e u r i n e o f r a i n b o w s d u r i n g r e s t , c o n t r o l l e d swimming a t v a r i o u s s p e e d s , a n d r e c o v e r y . T h e r e a c t u a l l y d i d o c c u r an i n c r e a s e d s o d i u m l o s s t h r o u g h t h e k i d n e y a s s o c i a t e d w i t h d i u r e s i s d u r i n g swimming, b u t t h e m a g n i t u d e o f t h i s d i s c h a r g e was e x t r e m e l y l o w r e l a t i v e t o t h e e s t i m a t e o f r e n a l e f f l u x c a l c u l a t e d i n t h e p r e s e n t s e c t i o n . T a b l e X I c o m p a r e s t h e maximum r e n a l d i s c h a r g e o f t h e e l e c t r o l y t e o b s e r v e d i n S e c t i o n I I I w i t h t h e u r i n a r y r e l e a s e c a l c u l a t e d b y s u b t r a c t i o n o f t h e s o d i u m e f f l u x r a t e o f t h e 121 T a b l e X. U r i n a r y sodium e f f l u x r a t e s o f shams under d i f f e r e n t e x e r c i s e c o n d i t i o n s e s t i m a t e d by s u b t r a c t i o n o f the mean b r a n c h i a l e f f l u x r a t e o f the u r i n a r y b l o c k a g e group from the mean whole animal e f f l u x r a t e o f the shams. E x e r c i s e c o n d i t i o n C a l c u l a t e d u r i n a r y sodium e f f l u x r a t e (ug/100 g/minute) • 1 s t hour swimming 21.72 2nd hour swimming 14.88 subsequent hours swimming 5.82 i n t e r m i t t e n t 3.39 1 s t hour r e c o v e r y 7.53 2nd hour r e c o v e r y 1.25 subsequent hours r e c o v e r y 6.86 * Computed assuming an e f f l u x r a t e f o r subsequent hours swimming i n u r i n a r y b l o c k a g e f i s h e q u a l t o 13.81 ug/100 g/minute, the average o f 2nd hour swimming and i n t e r m i t t e n t v a l u e s . 122 T a b l e X I . C o m p a r i s o n o f c a l c u l a t e d r e n a l s o d i u m e f f l u x r a t e s d u r i n g swimming i n shams w i t h r e p o r t e d d i r e c t m e a s u r e m e n t s o f maximum u r i n a r y s o d i u m d i s c h a r g e i n Salmo g a i r d n e r i • U r i n a r y S o d i u m e f f l u x r a t e . ( u g/100 g / m i n u t e ) C o n d i t i o n s M e t h o d R e f e r e n c e 6.86 c o n t r o l ( s u b s e q u e n t c a l c u l a t i o n p r e s e n t s t u d y h o u r s swimming) S e c t i o n I I * 21.72 1 s t h o u r swimming " " up t o 32 c m / s e c . * 14.88 2nd h o u r swimming " " up t o 32 c m / s e c . 1,95 c o n t r o l d i r e c t p r e s e n t s t u d y m e a s u r e m e n t S e c t i o n I I I * 3.51 1 s t h o u r swimming " " - 21.4 c m / s e c . * 2.61 1 s t h o u r swimming " " - 32.1 c m / s e c . * 2.83 1 s t h o u r swimming " " - 42.8 c m / s e c . 1.43 c o n t r o l 5.35 1 h o u r a f t e r a c u t e h y p o x i a d i r e c t Hunn (1969) m e a s u r e m e n t 0.30 c o n t r o l d i r e c t Hunn and W i l l -m e a s u r e m e n t f o r d (19 70) * 3.38 6 h o u r s a f t e r " " MS 222 a n a e s t h e s i a 4.71 *2 h o u r s a f t e r " " m e t h y l p e n t y n o l a n a e s t h e s i a * Maximum u r i n a r y s o d i u m l o s s u n d e r d i f f e r e n t e x p e r i m e n t a l t r e a t -m e n t s . 123 u r i n a r y b l o c k a g e f i s h f r o m t h e c o r r e s p o n d i n g sham v a l u e . A number o f o t h e r d i r e c t m e a s u r e m e n t s o f t h e maximum r e n a l s o d i u m l o s s o f Salmo g a i r d n e r i i n r e s p o n s e t o v a r i o u s s t r e s s e s h a s b e e n i n c l u d e d f r o m t h e work o f Hunn (Hunn,1969; Hunn and W i l l f o r d , 1 9 7 0 ) . T h e s e d a t a i n d i c a t e t h a t r a t h e r t h a n comp-r i s i n g o v e r h a l f t h e w h o l e o r g a n i s m e f f l u x r a t e d u r i n g t h e f i r s t a n d s e c o n d h o u r s o f e x e r c i s e , as t h e c a l c u l a t i o n s s u g g e s t , u r i n a r y s o d i u m l o s s c a n p r o b a b l y a c c o u n t f o r no more t h a n a b o u t 15% o f t h e u n i d i r e c t i o n a l o u t w a r d movement. T h i s e v i d e n c e , a l t h o u g h n o t c o n c l u s i v e , s t r o n g l y s u g g e s t s t h a t b r a n c h i a l s o d i u m e f f l u x r a t e s o f u r i n a r y b l o c k a g e f i s h w ere a b n o r m a l l y lo w ; a p o s s i b l e c a u s e f o r t h i s i r r e g u l a r i t y w i l l be a d v a n c e d p r e s e n t l y . C o n s e q u e n t l y , i n n o n - o c c l u d e d a n i m a l s , m o s t o f t h e v a r i a t i o n s i n e f f l u x r a t e a s s o c i a t e d w i t h swimming p r o b a b l y o c c u r r e d a t t h e g i l l s . T he b r a n c h i a l e f f l u x r a t e o f t h e shams w o u l d t h e r e f o r e h a v e b e e n a p p r o x i m a t e l y 30 ug/100 g / m i n . d u r i n g t h e f i r s t h o u r o f swimming, a f i g u r e n e a r l y i d e n t i c a l t o t h a t o b s e r v e d d u r i n g one h o u r o f c h a s i n g i n S e c t i o n I . I n a d d i t i o n , t h e unknown c o m p e n s a t o r y m e c h a n i s m r e s p o n s i b l e f o r t h e r e d u c t i o n o f e f f l u x d u r i n g p r o l o n g e d a c t i v i t y w o u l d h a v e b e e n l a r g e l y a c t i v e o n t h e b r a n c h i a l c omponent o f s o d i u m l o s s . D a t a d e r i v e d f r o m t h e w e i g h i n g p r o c e d u r e and a n a l y s i s o f t e r m i n a l b l o o d a n d t i s s u e s a m p l e s h a s b e e n s u m m a r i z e d i n T a b l e X I I . • The r a d i o s o d i u m s p a c e o f t h e n o r m a l r a i n b o w t r o u t , w h i c h a t 8 h o u r s a f t e r e x t e r n a l a d m i n i s t r a t i o n o f t h e r a d i o -i s o t o p e p r o b a b l y r e p r e s e n t e d an e q u i l i b r i u m v a l u e ( M a y e r an d N i b e l l e , 1 9 6 9 ) was v e r y s i m i l a r t o t h e few o t h e r m e a s u r e m e n t s r e p o r t e d f o r " i n t a c t " f r e s h w a t e r t e l e o s t s ( M a e t z , 1 9 5 6 ; M o t a i s , 22 1967; L a h l o u e t a l . , 1 9 6 9 ) . B o t h Na d i s t r i b u t i o n v o l u m e s 124 Table XII. Terminal measurements of i n t e r n a l sodium and water l e v e l s , radiosodium spaces, hematocrits, and weight changes over the experimental period. Means - 1 standard e r r o r . Normal Sham Urinary blockage N = 10 N = 10 N = 9 Plasma sodium 144.75 ± 5.23 132.62 ± 10.05 106.69 ± 3. 87 concentration P l < .001 (mEq/L) p-^  „== n.s. -P2 < .05 22 Na space 33.82 ± 1.83 29.86 ± 1.43 34.39 ± o. 78 (ml/100 g) p^ = n.s. P i " n.s. P 2 < .02 T o t a l exchange-Ill,426. 00 ± 89 ,957.50 ± 84,399.90 ± able i n t e r n a l 5,867. 11 6 ,629.68 3.808.42 sodium p 1< .05 .01 (ug/100 g) P i < P 2 " n.s. Plasma water "96.19 ± 0.26 95.90 ± 0.27 96.38 ± 0. 31 concentration p^ = n.s. '(ml/100g plasma) p l = n.s. P 2 - n.s. Hematocrit {%) 28.05 -3.17 33.75 ± 2.56 28.49 ± 3. 86 p^ = n.s. P l = n.s. P2 = n.s. Weight change - -2.57 ± 1 . 0 5 + 8 . 5 7 ± 0 . 9 3 (g/lOOg i n i t i a l weight) p l ~ p l ~ " P 2 < .001 Tissue water 81.047 ± 0.530 81.851 ± 0.570 83.899 ± 0.257 concentration n_ (ml/lOOg/tissue) P x =• n.s. P1< .oui P 2 < * 0 1 equals s i g n i f i c a n c e with respect to corresponding normal value p 2 equals s i g n i f i c a n c e with respect to corresponding sham value a n d p l a s m a s o d i u m l e v e l s were l o w e r i n t h e shams t h a n t h e n o r m a l s , a l t h o u g h n e i t h e r d i f f e r e n c e was s i g n i f i c a n t b y i t s e l f . T h e e f f e c t i v e p r o d u c t s o f t h e s e p a r a m e t e r s , t o t a l e x c h a n g e a b l e i n t e r n a l sodium, d i d h o w e v e r show a s t a t i s t i c a l l y c o n f i r m e d d e c r e a s e . D i s t u r b a n c e s i n e l e c t r o l y t e b a l a n c e f o r up t o 72 h o u r s a f t e r MS 222 a n a e s t h e s i a a n d o p e r a t i v e p r o c e d u r e s may be a s s o c i a t e d w i t h an i n c r e a s e i n e f f e c t i v e b r a n c h i a l p e r m e a b i l i t y a c c o m p a n y i n g e l e v a t i o n o f r e s p i r a t o r y e x c h a n g e d u r i n g t h e r e c o v e r y p e r i o d ( H o u s t o n e t a l . , 1 9 6 9 ) . As d i s c u s s e d i n S e c t i o n I , a g r e a t e r l e a k a g e o f s o d i u m o u t a c r o s s t h e g i l l c o u l d r e s u l t f r o m t h i s p e r m e a b i l i t y i n c r e a s e . The t r o u t b l a d d e r i s c o n t r a c t i l e i n n a t u r e ( L e d e r i s , 1 9 7 0 ) a n d p r o b a b l y r e l e a s e s u r i n e i n t e r m i t t e n t l y . R e c e n t u n p u b l i s h e d s t u d i e s ( H i r a n o , p e r s o n a l c o m m u n i c a t i o n t o D . J . R a n d a l l ) h a v e d e m o n s t r a t -e d a s o d i u m t r a n s p o r t c a p a c i t y i n t h e i s o l a t e d b l a d d e r w a l l o f Salmo g a i r d n e r i , a l t h o u g h i t s f u n c t i o n i n t h e i n t a c t a n i m a l i s n o t y e t u n d e r s t o o d . I t i s t h e r e f o r e p o s s i b l e t h a t a s e c o n d a r y s o d i u m c o n s e r v a t i o n m e c h a n i s m i n s e r i e s w i t h t h e t u b u l a r r e -a b s o r p t i v e a c t i v i t y n o r m a l l y i n c r e a s e s t h e e f f i c i e n c y o f s o d i u m r e t e n t i o n . The u r i n a r y c a t h e t e r w o u l d d r a i n t h e b l a d d e r o f u r i n e as s o o n as i t was p r o d u c e d an d t h u s n e g a t e t h i s r e a b s o r p t i v e f u n c t i o n , t h e r e b y f u r t h e r a u g m e n t i n g t h e s o d i u m d e f i c i t o f t h e c a n n u l a t e d t r o u t . The s l i g h t l y h i g h e r w h o l e b o d y e f f l u x r a t e s r e c o r d e d u n d e r m o s t e x e r c i s e c o n d i t i o n s i n t h e shams ( F i g . 19) may t h e r e f o r e h a v e r e f l e c t e d e l e v a t i o n o f b o t h b r a n c h i a l a n d r e n a l l o s s e s . However as n o t e d e a r l i e r , t h e p r e s e n c e o f t h e u r i n a r y c a n n u l a d i d n o t i n t e r f e r e w i t h t h e p a t t e r n o f e f f l u x c h a n g e s e x h i b i t e d d u r i n g e x t e n d e d e x e r c i s e . A v e r y s i g n i f i c a n t w e i g h t g a i n a m o u n t i n g t o a n e t w a t e r 126 entry of about 1% body volume per hour occurred i n the urinary blockage animals (Table X I I ) . (Shams underwent a 2.5 g/100 g weight reduction over the experimental period; a smaller but s i g n i f i c a n t weight l o s s associated with extended swimming was observed under more c a r e f u l l y c o n t r o l l e d conditions i n Section I I I ) . On autopsy, the l i g a t e d f i s h e x h i b i t e d some di s t e n s i o n of the urogenital p a p i l l a e although the volume con-tained i n the bladder i t s e l f d i d not appear to be l a r g e . I t seems probable that the accumulation of urine i n t h i s organ continued only u n t i l i t s h y d r o s t a t i c pressure, r e f e r r e d back to the kidney tubules, opposed the glomerular f i l t r a t i o n pressure. This e f f e c t may have been accelerated by the known c o n t r a c t i l i t y of the bladder (Lederis,1970). Thus most of the i n f l u x e d water was probably not removed from the blood by the kidney. Plasma water concentration was however only marginally (and n o n - s i g n i f i c a n t l y ) elevated i n the l i g a t e d trout and hematocrit remained s i m i l a r to that of the other two groups. The imple-mentation of some mechanism to prevent excessive expansion of the i n t r a v a s c u l a r volume was therefore i n d i c a t e d . The extreme-l y s i g n i f i c a n t augmentation of t i s s u e water l e v e l s suggested that t h i s compensation involved accumulation of the superfluous water i n e i t h e r or both the i n t r a c e l l u l a r and e x t r a c e l l u l a r phases of the extravascular space. Plasma sodium l e v e l s were d r a s t i c a l l y depressed despite the apparent s t a b i l i t y of plasma volume and t o t a l exchangeable i n t e r n a l sodium. I t would therefore appear that the removal of excess water from the vascular compartment was accompanied by a r e d i s t r i b u t i o n of body sodium which was r e f l e c t e d i n a s i g n i f i c a n t expansion of the radiosodium space r e l a t i v e to the shams. As sodium appears to b e e f f e c t i v e l y e x c l u d e d f r o m t h e i n t r a c e l l u l a r s p a c e i n s a l m o n i d s ( H o u s t o n , 1 9 6 4 ; Toews,1969) a n e t movement o f t h i s i o n i n t o t h e i n t e r s t i t i a l f l u i d s t o h e l p m a i n t a i n t h e c o n s t a n c y o f t h e i m m e d i a t e l y e x t r a c e l l u l a r m i l i e u may w e l l h a v e o c c u r r e d a t t h e e x p e n s e o f p l a s m a h o m e o s t a s i s . T h i s p r o f o u n d d r o p i n p l a s m a s o d i u m l e v e l s c o u l d h a v e b e e n r e s p o n s i b l e f o r t h e d e p r e s s i o n o f b r a n c h i a l e f f l u x r a t e e a r l i e r p o s t u l a t e d t o h a v e o c c u r r e d i n t h e u r i n a r y b l o c k a g e t r o u t . I n f u s i o n o f h y p o t o n i c s a l i n e s t i m u l a t e d t h e n e t u p t a k e o f s o d i u m a c r o s s t h e g i l l s o f t h e g o l d f i s h , C a r a s s i u s a u r a t u s ( B o u r g u e t e t a]..,1964) a n d t h e e e l , A n g u i l l a a n g u i l l a f ( M a y e r an d N i b e l l e , 1 9 7 0 ) , w h i l e a d m i n i s t r a t i o n o f a h y p e r t o n i c s o l u t i o n r e v e r s e d t h i s e f f e c t . The f o r m e r r e s p o n s e o c c u r r e d t h r o u g h t h e e l e v a t i o n o f t h e i n f l u x c omponent a l o n e , w h i l e t h e l a t t e r i n v o l v e d b o t h i n h i b i t i o n o f i n f l u x and a u g m e n t a t i o n o f e f f l u x . A t l e a s t i n t h e g o l d f i s h , t h e r e s p o n s e s were d i r e c t l y m e d i a t e d b y t h e c h a n g e s i n p l a s m a s o d i u m l e v e l s r e s u l t i n g f r o m t h e i n j e c t i o n s . The ammocoete,, L a m p e t r a p l a n e r i t i n c r e a s e d n e t u p -t a k e i n r e s p o n s e t o e x p e r i m e n t a l s o d i u m d e p l e t i o n t h r o u g h b o t h e l e v a t i o n o f i n f l u x a n d d e p r e s s i o n o f e f f l u x p a r a m e t e r s ( M o r r i s a n d B u l l , 1 9 7 0 ) . T h e n e t s o d i u m f l u x a c r o s s i s o l a t e d h e m i b r a n c h s o f Salmo g a i r d n e r i was i n v e r s e l y p r o p o r t i o n a l t o t h e s o d i u m c o n c e n t r a t i o n o f t h e p e r f u s i o n f l u i d ( R i c h a r d s a n d Fromm, 1970).' A t i n t e r n a l s o d i u m c o n c e n t r a t i o n s i n f e r i o r t o n o r m a l p l a s m a s o d i u m l e v e l s t h e r e o c c u r r e d a n e t i n w a r d move-ment o f t h e e l e c t r o l y t e , w h i l e t h e o p p o s i t e o c c u r r e d a t h i g h s o d i u m c o n c e n t r a t i o n s o f t h e p e r f u s i o n s o l u t i o n . T h i s i n v e s t -i g a t i o n d i d n o t , however, s e p a r a t e t h e r e l a t i v e c o n t r i b u t i o n s o f t h e two u n i d i r e c t i o n a l f l u x c o m p o n e n t s t o t h e o b s e r v e d 128 e f f e c t s . T h e d a t a o f t h e p r e s e n t s t u d y i n d i c a t e t h a t b r a n c h i a l s o d i u m i n f l u x o f r a i n b o w t r o u t i s r e m a r k a b l y s t a b l e i n v i v o ; t h e same i s n o t , h o w e v e r t t r u e o f t h e e f f l u x p a r a m e t e r . I n f l u x was a p p a r e n t l y u n a f f e c t e d b y t h e p l a s m a s o d i u m d e p l e t i o n a s s o c i a t e d w i t h r e n a l b l o c k a g e ( F i g . 1 9 ) . T h u s i n t h i s s p e c i e s , m o d i f i c a t i o n o f n e t s o d i u m t r a n s p o r t a c r o s s t h e g i l l s may n o r m a l l y o c c u r t h r o u g h a l t e r a t i o n s i n t h e o u t w a r d m o v i n g comp-o n e n t a l o n e . I n d e e d some d e c r e m e n t i n p a s s i v e e f f l u x w o u l d b e e x p e c t e d s i m p l y f r o m t h e d e c l i n e i n t h e p l a s m a t o water s o d i u m c o n c e n t r a t i o n g r a d i e n t c a u s e d b y r e d u c t i o n s i n p l a s m a s o d i u m l e v e l s , a n d c o u l d be r e i n f o r c e d b y an i n d u c e d d e c r e a s e o f b r a n c h i a l p e r m e a b i l i t y . The e x i s t e n c e o f s u c h a m e c h a n i s m w o u l d e x p l a i n t h e d e p r e s s i o n o f b r a n c h i a l e f f l u x p r o p o s e d t o accompany u r i n a r y l i g a t i o n . H e n c e u r i n a r y b l o c k a g e w o u l d a p p e a r t o be an e x t r e m e l y u n s a t i s f a c t o r y t e c h n i q u e i n l i g h t o f t h e m a s s i v e d i s t u r b a n c e i n i n t e r n a l h y d r o e l e c t r o l y t e h o m e o s t a s i s a s s o c i a t e d w i t h t h e p r o c e d u r e a n d i t s l i k e l y c o n s e q u e n c e s w i t h r e s p e c t t o s o d i u m e x c h a n g e s . C o n c l u s i o n s a b o u t s o d i u m f l u x b e h a v i o u r b a s e d on i t s u s e ( e . g . H o l m e s , 1 9 5 9 ) must be g r a v e l y s u s p e c t . The o c c l u s i o n e x p e r i m e n t s were t h e r e f o r e u n i n f o r m a t i v e i n d i s c r i m -i n a t i n g b e t w e e n b r a n c h i a l and r e n a l c o n t r i b u t i o n s t o t h e s o d i u m e f f l u x c h a n g e s m e a s u r e d d u r i n g p r o l o n g e d e x e r c i s e . E v i d e n c e f r o m o t h e r s o u r c e s , however, i n d i c a t e d t h a t t h e m a j o r i t y o f e f f l u x r a t e v a r i a t i o n , i n c l u d i n g t h e c o m p e n s a t o r y r e d u c t i o n i n s o d i u m l o s s d u r i n g e x t e n d e d swimming, i n v o l v e d b r a n c h i a l f u n c t i o n . T h e p o s s i b l e n a t u r e and m e c h a n i s m o f t h i s a d j u s t i v e phenomenon w i l l be c o n s i d e r e d i n t h e G e n e r a l D i s c u s s i o n . 12 B. The C o n c e n t r a t i o n D e p e n d e n c e o f B r a n c h i a l S o d i u m F l u x e s A s e a c h e x p e r i m e n t i n t h i s s e c t i o n e n t a i l e d e i g h t h o u r l y f l u x r a t e m e a s u r e m e n t s , o v e r 2 30 i n d i v i d u a l v a l u e s f o r e a c h u n i d i r e c t i o n a l s o d i u m movement were o b t a i n e d f r o m 29 t r o u t . T h e l a r g e e x t e r n a l c o n c e n t r a t i o n c h a n g e s e f f e c t e d o v e r t h e e x -p e r i m e n t a l p e r i o d b y t h e n e t f l u x e s o f t h e a n i m a l s p r o d u c e d m e a s u r e m e n t s a t a w i d e v a r i e t y o f w a t e r s o d i u m l e v e l s . T h e r e s u l t s p r e s e n t e d i n P a r t A o f S e c t i o n I I i n d i c a t e d t h a t b r a n c h i a l s o d i u m i n f l u x was i n s e n s i t i v e t o t h e e x e r c i s e c o n d -i t i o n o r e x p e r i m e n t a l t r e a t m e n t o f t h e t r o u t ( F i g . 1 9 ) . I t t h e r e f o r e seemed v a l i d t o a n a l y z e t h e i n t e r a c t i o n b e t w e e n e x t e r n a l s o d i u m l e v e l a n d b r a n c h i a l i n f l u x r a t e u s i n g a l l a v a i l -a b l e p a i r e d m e a s u r e m e n t s (231) o f t h e s e p a r a m e t e r s . C o n s e q u e n t l y a l l h o u r l y v a l u e s o f s o d i u m i n f l u x r a t e w e r e a s s i g n e d t o c a t e g o r i e s on t h e b a s i s o f t h e a v e r a g e a m b i e n t w a t e r s o d i u m l e v e l o v e r t h e p a r t i c u l a r p e r i o d . The mean i n f l u x v a l u e f o r e a c h 0.2 ug/ml r a n g e , p l o t t e d a t t h e m i d p o i n t s o f t h e i n t e r v a l s , a r e p r e s e n t e d i n F i g . 20. A s n o t e d e a r l i e r , means a t s o d i u m l e v e l s b e l o w 0.8 ug/ml d e m o n s t r a t e d an o b v i o u s p o s i t i v e c o r r e l a t i o n w i t h e x t e r n a l c o n c e n t r a t i o n s ; t h i s was n o t t r u e a t s o d i u m l e v e l s g r e a t e r t h a n t h i s f i g u r e . T h e f o r m o f t h e r e l a t i o n s h i p o v e r t h e w h o l e c o n c e n t r a t i o n r a n g e was s i m i l a r t o t h a t o b s e r v e d f o r a v a r i e t y o f s o d i u m - t r a n s p o r t i n g s y s t e m s - e . g . i s o l a t e d f r o g s k i n ( U s s i n g , 1 9 4 9 b ; K i r s c h n e r , 1 9 5 5 ) ; i s o l a t e d t o a d b l a d d e r ( F r a z i e r e t a l . , 1 9 6 2 ) ; w h o l e c r a y f i s h ( S h a w , 1 9 5 9 ) ; w h o l e gammarid c r u s t a c e a n s ( S u t c l i f f e a nd Shaw,1968); w h o l e ammocoetes ( M o r r i s a n d B u l l , 1 9 7 0 ) ; and t h e p e r f u s e d g i l l s o f a n a e s t h e t i z e d r a i n b o w t r o u t ( K e r s t e t t e r et a l . , 1 9 7 0 ) . 130 Figure 20 The r e l a t i o n s h i p between branchial sodium i n f l u x r a t e and external sodium concentration. A l l data from normal, sham, and urinary blockage treatment groups has been averaged over 0.2 ug/ml sodium concentration i n t e r v a l s . Means - 1 standard error are p l o t t e d at the midpoints of each i n t e r v a l . The l i n e f i t t e d to the points was generated by the Kirschner (1955) equation: where Hsra]o = external sodium concentration F i = Fi(max). H o F i " S o d i u m i n f l u x r a t e Ks + |Na] o Fi(max) = maximum sodium i n f l u x r a t e Ks = h a l f - s a t u r a t i o n constant Values for Fi(max) and Ks were obtained from a Lineweaver-Burke p l o t of the data. EXTERNAL SODIUM CONCENTRATION (jjg/ml ) 131 K i r s c h n e r (1955), assuming the i m p l i c a t i o n o f a s p e c i f i c c a r r i e r w i t h which sodium complexed i n the t r a n s p o r t p r o c e s s , d e v e l o p e d a t h e o r e t i c a l r e l a t i o n s h i p d e s c r i b i n g the r a t e l i m i -t e d n a t u r e o f i n f l u x t hrough the f r o g s k i n . When the concen-t r a t i o n g r a d i e n t between i n t e r n a l and e x t e r n a l media i s l a r g e , t h e s i m p l e d i f f u s i o n c o n s t i t u e n t o f the e q u a t i o n may be i g n o r e d and the r e l a t i o n s h i p becomes F i = F i ( m a x ) . [Na] o  Ks + [Na] o where [Na] o = e x t e r n a l sodium c o n c e n t r a t i o n F i = sodium i n f l u x r a t e Fi(max) = maximum sodium i n f l u x r a t e Ks = h a l f - s a t u r a t i o n c o n s t a n t which has a form i d e n t i c a l t o the f a m i l i a r M i c h a e l i s - M e n t e n e q u a t i o n r e l a t i n g enzymatic r e a c t i o n r a t e to s u b s t r a t e con-c e n t r a t i o n . A double r e c i p r o c a l p l o t (Lineweaver and Burke, 1934) o f the p r e s e n t d a t a y i e l d e d v a l u e s f o r Fi(max:) and Ks which were used to g e n e r a t e a c u r v e d e s c r i b i n g F i at d i f f e r e n t JNaJo's. T h i s t h e o r e t i c a l c u r v e i s the l i n e f i t t e d to the v a l u e s i n F i g . 2 0 . The c o n c e n t r a t i o n dependence o f sodium i n f l u x a c r o s s the g i l l s o f i n t a c t Salmo g a i r d n e r i i s w e l l des-c r i b e d by the K i r s c h n e r e q u a t i o n . S i m i l a r a c c o r d has been demonstrated ,in the c r a y f i s h , A s t a c u s p a l l i p e s . the ammocoete Lampetra p l a n e r i , and the g i l l s o f a n a e s t h e t i z e d rainbow t r o u t ( K e r s t e t t e r e t aJL.,1970; K i r s c h n e r , 1 9 7 0 ) . As Shaw (1959) has p o i n t e d out, t h e r e i s n o t h i n g s i n g u l a r about c o i n c i d e n c e o f t h e d a t a w i t h the K i r s c h n e r r e l a t i o n s h i p , and o t h e r e x p r e s s i o n s may e x i s t which d e s c r i b e the p r o c e s s more a c c u r a t e l y ( e . g . t h r o u g h a l s o c o n s i d e r i n g p o t e n t i a l d i f f e r e n c e ) . However, the 132 c o r r e s p o n d e n c e d o e s s u g g e s t a s a t u r a b l e r a t e l i m i t e d s y s t e m b a s e d on a c o m p l e x i n g c a r r i e r ( K i r s c h n e r , 1 9 5 5 ) , and a g e n e r a l s i m i l a r i t y t o o t h e r r e p o r t e d a c t i v e s o d i u m t r a n s p o r t m e c h a n i s m s . The Ks and F i ( m a x ) v a l u e f o r Salmo g a i r d n e r i d e r i v e d f r o m t h e p r e s e n t d a t a ( F i g . 20) were 0.32 ug/ml (0.014 mEq/L) and 22.38 ug/100 g / m i n u t e (58.40 uEq/100 g / h o u r ) r e s p e c t i v e l y . T a b l e X I I I c o m p a r e s t h e s e f i g u r e s w i t h v a l u e s f r o m an a s s o r t -ment o f o t h e r s y s t e m s . The t r a n s p o r t s y s t e m o f r a i n b o w t r o u t i n t h i s s t u d y o b v i o u s l y d e m o n s t r a t e d an e x t r e m e l y h i g h s o d i u m a f f i n i t y r e l a t i v e t o t h a t o f o t h e r a n i m a l s . However, i t must be n o t e d t h a t t h e Ks v a l u e o f t h e p r e s e n t s t u d y i s 30 t i m e s l o w e r t h a n t h a t o b t a i n e d b y K e r s t e t t e r e t _ a l . (19 70) f o r t h e same s p e c i e s , w i t h l e s s e r d i s s i m i l a r i t i e s i n F i ( m a x ) . T h e s e d i s c r e p a n c i e s may h a v e a r i s e n f r o m t h e e x t r e m e l y d i f f e r -e n t e x p e r i m e n t a l c o n d i t i o n s o f t h e r e s p e c t i v e i n v e s t i g a t i o n s . T h e p r e s e n t t r o u t were i n a r e l a t i v e l y n o r m a l s t a t e , w h i l e t h e t h e r a i n b o w s o f K e r s t e t t e r et. a l . (19 70) were i n a d i s t i n c t l y u n p h y s i o l o g i c a l c o n d i t i o n . T h e s e w o r k e r s u s e d MS 222 a n a e s t h e t i z e d f i s h h e l d u p s i d e down and p e r f u s e d a t 100 m l / m i n u t e t h r o u g h a #15 n e e d l e sewn i n t o t h e b u c c a l c a v i t y . S u c h a s y s -tem w o u l d h a v e i n v o l v e d o n l y a s m a l l p o r t i o n o f t h e n o r m a l b r a n c h i a l a r e a and was p r o b a b l y i n a d e q u a t e t o s a t i s f y t h e g a s e x c h a n g e r e q u i r e m e n t s o f t h e a n i m a l ( D a v i s and C a m e r o n , 1 9 7 0 ) . T h e l a t t e r e f f e c t i s s u f f i c i e n t t o a c c o u n t f o r t h e d i f f e r e n c e i n maximum i n f l u x r a t e on a b o d y w e i g h t b a s i s , w h i l e t h e g e n e r a l m e t a b o l i c d e p r e s s i o n r e s u l t i n g f r o m a n a e s t h e s i a c o u l d w e l l h a v e e l e v a t e d t h e o b s e r v e d K s . I f t h e c o n c e n t r a t i o n d e p e n d e n c e c u r v e o f s o d i u m i n f l u x i n t r o u t g i l l i s d e t e r m i n e d i n some way b y t h e p e r m e a b i l i t y c h a r a c t e r i s t i c s o f t h e membranes 133 T a b l e X I I I . Summary o f maximum s o d i u m i n f l u x r a t e s ( F i ( m a x ) ) a n d h a l f s a t u r a t i o n c o n c e n t r a t i o n s ( K s ) f o r s o d i u m u p t a k e s y s t e m s i n a v a r i e t y o f a n i m a l s . Ks (mEq/L .014 0.46 0.26 0.13 0.25 4.3 20 0.15 0.5 F i ( m a x ) ( u E g / l O O g / h o u r 58.40 33.30 36.00* 45.00* , 97 200 ^ 1 0 0 0 P r e p a r a t i o n w h o l e i n t a c t r a i n b o w t r o u t , S a l m o g a i r d n e r i g i l l s o f p e r f u s e d , a n a e s t h e t i z e d r a i n b o w t r o u t , S a l m o g a i r d n e r i w h o l e ammocoete, L a m p e t r a p l a n e r i s o d i u m d e p l e t e d w h o l e ammocoete, L a m p e t r a p l a n e r i w h o l e c r a y f i s h , A s t a c u s p a l l i p e s i s o l a t e d f r o g s k i n , Rana s p . i s o l a t e d t o a d b l a d d e r , B u f o  m a r i n u s a m p h i p o d c r u s t a c e a n , Gammarus p u l e x a m p h i p o d c r u s t a c e a n , Gammarus d u e b e n i R e f e r e n c e p r e s e n t s t u d y K e r s t e t t e r e t a l , (197 0 ) M o r r i s a n d B u l l ( 1 970) M o r r i s a n d B u l l ( 1970) Shaw (1959) K i r s c h n e r (1955) F r a z i e r e t a l (1962) S u t c l i f f e a n d Shaw (1968) S u t c l i f f e a n d Shaw (1968) * c o r r e c t e d f r o m an a p p a r e n t t y p o g r a p h i c a l e r r o r i n t h e p a p e r . 134 t h r o u g h w h i c h t h e i o n must p a s s b e f o r e b i n d i n g w i t h t h e c a r r i e r , a s a p p a r e n t l y o c c u r s i n t h e t o a d b l a d d e r ( F r a z i e r e t a l . , 1 9 6 2 ) , t h e n an i n c r e a s e i n d i f f u s i o n r e s i s t a n c e r e s u l t i n g f r o m i n -e f f i c i e n t g i l l p e r f u s i o n c o u l d a l s o h a v e r a i s e d t h e K s . The w a t e r s o d i u m l e v e l t o w h i c h r a i n b o w s were a c c l i m a t e d and i n w h i c h f l u x r a t e s were m e a s u r e d was d e t e r m i n e d b y t h e n a t u r e o f V a n c o u v e r t a p w a t e r , w h i c h c o n t a i n s v e r y l o w l e v e l s o f t h i s i o n ( g e n e r a l l y l e s s t h a n 2.0 ug/ml o r .09 mEq/L; s e e H o l m e s a n d S t a i n e r , 1 9 6 6 ) . . T h e t r o u t o f K e r s t e t t e r jet a l . w e r e p r e a d a p t e d t o a s o d i u m c o n c e n t r a t i o n a b o u t 10 t i m e s h i g h e r t h a n t h a t i n t h e p r e s e n t s t u d y . M o r r i s a n d B u l l ( 1 9 6 8 , 1970) h a v e shown t h a t t h e Ks o f s o d i u m i n f l u x i n t h e ammocoete c o u l d be m a r k e d l y r e d u c e d b y p r e t r e a t m e n t w i t h d i l u t e s o l u t i o n s ; F i ( m a x ) , on t h e o t h e r h a n d , was e l e v a t e d b y t h i s p r o c e d u r e . I n d e e d S u t c l i f f e and Shaw (1968) h a v e d e m o n s t r a t e d t h a t r a c e s o f t h e a m p h i p o d Gammarus d u e b e n i l i v i n g i n s t r e a m s w i t h l o w s o d i u m c o n c e n t r a t i o n s e x h i b i t Ks v a l u e s c o n s i d e r a b l y s m a l l e r t h a n t h o s e o f o t h e r r a c e s o f t h e s p e c i e s p e r e n n i a l l y i n h a b i t i n g e n v i r o n m e n t s i n w h i c h t h e i o n i s more a b u n d a n t . T h u s t h e q u a n t i t a t i v e d i f f e r e n c e i n t h e r e s u l t s o f t h e p r e s e n t s t u d y a n d t h a t o f K e r s t e t t e r e t j i l . ( 1 9 70) on t h e same s p e c i e s may a l s o r e f l e c t a d a p t a t i o n a l o r p e r h a p s e v e n g e n e t i c i n f l u e n c e s on t h e e x p e r i m e n t a l s t o c k s . T h e r e e x i s t o n l y a few o t h e r m e a s u r e m e n t s o f t h e c o n -c e n t r a t i o n d e p e n d e n c e o f s o d i u m i n f l u x i n " i n t a c t " f r e s h w a t e r f i s h , a n d a l l were o b t a i n e d a t s o d i u m c o n c e n t r a t i o n s o f t h e a c c l i m a t i o n a n d e x p e r i m e n t a l m e d i a c o n s i d e r a b l y g r e a t e r t h a n those., u s e d h e r e . However c o m p a r i s o n o f t h e t r o u t c u r v e w i t h t h i s l i m i t e d i n f o r m a t i o n ( F i g . 21) d o e s e m p h a s i z e t h e 135 F i g u r e 21 C o m p a r i s o n o f t h e c o n c e n t r a t i o n d e p e n d e n c e o f b r a n c h i a l s o d i u m i n f l u x i n t h e r a i n b o w t r o u t (1) w i t h t h a t r e -p o r t e d i n t h e g o l d f i s h ( 2 ) , t h e l a m p r e y ammocoete ( 3 ) , t h e e e l ( 4 ) , a n d t h e k i l l i f i s h ( 5 ) . L i n e s h a v e b e e n r e d r a w n f r o m d a t a p r e s e n t e d i n : (1) t h e p r e s e n t s t u d y ( F i g . 2 0 ) . T h i s c u r v e h a s b e e n e x t r a p o l a t e d ( a b r o k e n l i n e ) b e y o n d t h e r e g i o n o f d i r e c t d e t e r m i n a t i o n t h r o u g h u s e o f t h e K i r s c h n e r (1955) e q u a t i o n . (2) M a e t z ( 1 9 5 6 ) . (3) M o r r i s a n d B u l l ( 1 9 7 0 ) . (4) C h e s t e r J o n e s e t a l . ( 1 9 6 9 ) . (5) M a e t z e t a l . (1967 b ) . 60.0 EXTERNAL SODIUM CONCENTRATION (jjEq /m l ) 136 e x t r e m e l y h i g h e f f i c i e n c y o f t h i s a n i m a l ' s s y s t e m f o r s o d i u m u p t a k e f r o m d i l u t e s o l u t i o n s r e l a t i v e t o t h e e e l , A n g u i l l a  a n g u i l l a , t h e k i l l i f i s h , F u n d u l u s h e t e r o c l i t u s , and t h e l a m p r e y a m m o c o e t e / L a m p e t r a p l a n e r i . T h e d a t a o f M a e t z (1956) on t h e g o l d f i s ^ C a r a s s i u s a u r a t u s , h o w e v e r , show* a r a t e l i m i t e d t r e n d p a r a l l e l t o t h a t o f Salmo g a i r d n e r i down t o 0.1 uEq/ml , w h i c h may be i n d i c a t i v e o f a s i m i l a r h i g h a f f i n i t y t r a n s p o r t m e c h a n i s m . The p o s s i b l e o c c u r r e n c e o f a s o d i u m e x c h a n g e d i f f u s i o n e f f e c t i n t h e g i l l s o f r a i n b o w t r o u t was p r o p o s e d i n S e c t i o n I . A r g u m e n t s f o r t h i s phenomenon were b a s e d o n t h e e x t r e m e l y h i g h b r a n c h i a l f l u x r a t e s o f t r o u t r e l a t i v e t o o t h e r f r e s h w a t e r t e l e o s t s and t h e f a c t t h a t t h e e f f l u x o f s o d i u m a c r o s s t h e g i l l s d i d n o t a p p a r e n t l y i n c r e a s e i n p r o p o r t i o n t o t h e i r o x y g e n p e r m e a b i l i t y . E x c h a n g e d i f f u s i o n o f s o d i u m h a s n o t p r e v i o u s l y b e e n d e m o n s t r a t e d i n t h e b r a n c h i a l r e g i o n s o f f r e s h w a t e r t e l e o s t s , b u t , a p r i o r i , t h e r e seems no d e f i n i t e r e a s o n why i t c o u l d n o t e x i s t . S u c h a m e c h a n i s m e v i d e n t l y a c c o u n t s f o r 20 - 40% o f t h e n o r m a l s o d i u m e x c h a n g e o f t h e f r e s h w a t e r c r a y f i s h / A s t a c u s p a l l i p e s ;(Shaw,1959) and o f v a r i o u s g a m m a r i d a m p h i p o d s ( S u t c l i f f e a n d S haw,1968). A g e n e r a l c r i t e r i o n f o r t h e p r e s e n c e o f t h i s p r o c e s s i s c o v a r i a t i o n o f u n i d i r e c t i o n a l f l u x r a t e s w i t h c h a n g e s i n e x t e r n a l s o d i u m c o n c e n t r a t i o n , o r a m a r k e d r e d u c t i o n i n e f f l u x when i n f l u x i s a b o l i s h e d . To f u r t h e r p u r s u e t h e p r o b l e m , t h e e f f l u x r a t e s (70) o f t h e u r i n a r y b l o c k a g e g r o u p o f t r o u t a l o n e were a v e r a g e d o v e r 0.2 ug/ml s o d i u m c o n c e n t r a t i o n r a n g e s as p r e v i o u s l y d e s c r i b e d f o r i n f l u x r a t e s . T h e s e e f f l u x v a l u e s were g e n e r -a t e d b y a d m i t t e d l y a b n o r m a l a n i m a l s b u t were p r o d u c e d b y t h e 137 o n l y t r e a t m e n t g r o u p i n w h i c h m e a s u r e d s o d i u m movements were e x c l u s i v e l y b r a n c h i a l i n o r i g i n . As t h e i n f l u x r a t e s o f t h e s e f i s h w e r e i d e n t i c a l t o t h o s e o f n o r m a l r a i n b o w s ( F i g . 1 9 ) , i t seems u n l i k e l y t h a t t h e e x c h a n g e d i f f u s i o n component o f e f f l u x , i f p r e s e n t , w o u l d h a v e b e e n a f f e c t e d b y t r a u m a . I n a d d i t i o n , t h e u s e o f t h i s e d a t a was a d v a n t a g e o u s i n a s m u c h as t h e u n i -d i r e c t i o n a l l o s s o f s o d i u m a c r o s s t h e g i l l s , p e r h a p s due t o t h e e f f e c t o f p l a s m a s o d i u m d e p l e t i o n d i s c u s s e d e a r l i e r , was a p p a r e n t l y i n s e n s i t i v e t o t h e e x e r c i s e c o n d i t i o n o f t h e a n i m a l . T h e r e s u l t s a r e p r e s e n t e d i n F i g . 22. O v e r t h e c o n c e n t r a t i o n i n t e r v a l ( 0.10 - 1.50 ug/ml) f o r w h i c h a d e q u a t e d a t a was a v a i l a b l e , t h e r e p r e v a i l e d an a p p r o x i m a t e l y l i n e a r p o s i t i v e r e l a t i o n s h i p b e t w e e n e x t e r n a l c o n c e n t r a t i o n a n d b r a n c h i a l s o d -i um e f f l u x r a t e w h i c h l o o s e l y p a r a l l e l e d t h e c o n c e n t r a t i o n d e p e n d e n c e o f t h e i n f l u x p a r a m e t e r s o v e r t h e same r a n g e . T h i s p a t t e r n i s e x t r e m e l y s u g g e s t i v e o f e x c h a n g e d i f f u s i o n . K e r s t e t t e r e t a l . (1970) h a v e o b t a i n e d s i m i l a r c o r r e l a t i o n o f u n i d i r e c t i o n a l b r a n c h i a l f l u x r a t e s i n t h e i r p e r f u s e d t r o u t p r e p a r a t i o n s . T h u s , a t l e a s t o n t h e q u a l i t a t i v e n a t u r e o f t h e i n f l u x c u r v e and i n f l u x - e f f l u x l i n k a g e , t h e r e s u l t s o f t h e p r e s e n t s t u d y a n d t h a t o f K e r s t e t t e r e t a l . ( 1 9 70) a r e i n g o o d a g r e e m e n t . A s s u m i n g f o r t h e p r e s e n t t h a t e x c h a n g e d i f f u s i o n d o e s c o n t r i b u t e t o b r a n c h i a l s o d i u m t r a n s f e r , t h e n t h e e x t e n s i o n o f t h e e f f l u x c o n c e n t r a t i o n d e p e n d e n c e l i n e ( F i g . 22) t o z e r o e x t e r n a l s o d i u m s h o u l d a p p r o x i m a t e t h e n o n - c a r r i e r m e d i a t e d s o d i u m l e a k a c r o s s t h e g i l l s o f l i g a t e d f i s h . T h e e x t r a -p o l a t i o n y i e l d e d a v a l u e o f 2.3 ug/100 g / m i n u t e f o r t h e s i m p l e d i f f u s i o n component o f e f f l u x , w h i c h s h o u l d be s t a b l e o v e r t h e 138 F i g u r e 22 T h e r e l a t i o n s h i p b e t w e e n b r a n c h i a l s o d i u m e f f l u x r a t e a n d e x t e r n a l s o d i u m c o n c e n t r a t i o n . A l l v a l u e s f o r u r i n a r y b l o c k a g e a n i m a l s o n l y h a v e b e e n a v e r a g e d o v e r 0.2 ug/ml s o d i u m c o n c e n t r a t i o n i n t e r v a l s . Means - 1 s t a n d a r d e r r o r a r e p l o t t e d a t t h e m i d p o i n t s o f e a c h i n t e r v a l . T h e f i t t e d l i n e h a s b e e n e x t r a -p o l a t e d t o 0 e x t e r n a l s o d i u m l e v e l f o r t h e p u r p o s e s o f t h e c a l c u l a t i o n p r e s e n t e d i n T a b l e X I V . The c o n c e n t r a t i o n d e p e n d e n c e c u r v e o f s o d i u m i n f l u x r a t e f r o m F i g . 20 i s i n c l u d e d f o r c o m p a r i s o n . 05 , 1.0 1.5 2.0 2.5 3.0 EXTERNAL SODIUM CONCENTRATION ( jjg/ml ) 139 r e l a t i v e l y n a r r o w c o n c e n t r a t i o n r a n g e o f e x t e r n a l s o d i u m e n c o u n -t e r e d i n t h e s t u d y . C o n s e q u e n t l y , t h e c o n t r i b u t i o n o f d i f f e r -e n t m e c h a n i s m s t o b r a n c h i a l s o d i u m e x c h a n g e i n t h e l i g a t e d t r o u t c o u l d be c o m p u t e d f o r a w a t e r s o d i u m l e v e l o f 1.5 ug/ml f r o m t h e d a t a o f F i g s . 20 and 22. ( T h i s c o n c e n t r a t i o n h a s b e e n a r b i t r a r i l y c h o s e n as i t c o r r e s p o n d s t o t h e a v e r a g e l e v e l u s e d i n S e c t i o n I a n d r e p r e s e n t s a p o i n t w h e re b o t h i n f l u x ( F i g . 20) a n d e f f l u x ( F i g . 22) means l i e on t h e f i t t e d l i n e s ) . T h e r e s u l t s a r e p r e s e n t e d i n T a b l e X I V . I t i s e n c o u r a g i n g t o n o t e t h a t t h e s e f i g u r e s a r e i n e x c e l l e n t a g r e e m e n t w i t h t h o s e c a l c u l a t e d i n S e c t i o n I (pp.68,69) f o r r e s t i n g r a i n b o w s t h r o u g h a number o f a s s u m p t i o n s a b o u t c h a n g i n g b r a n c h i a l p e r m e a b i l i t y d u r i n g e x e r c i s e . The p r e s e n t d a t a t h e r e f o r e l e n d * c r e d e n c e t o t h e i d e a p r e s e n t e d i n S e c t i o n I t h a t t h e e f f e c t i v e p erm-e a b i l i t y o f t h e b r a n c h i a l e p i t h e l i u m t o s o d i u m i n c r e a s e d a b o u t 5 f o l d i n p a r a l l e l w i t h t h a t f o r o x y g e n d u r i n g t h e one h o u r o f c h a s i n g . However b o t h t h e o r i g i n a l i d e a and t h e s u p p o r t p r e s e n t e d h e r e a r e p r e s u m p t i v e o f e x c h a n g e d i f f u s i o n i n t h e s o d i u m t r a n s f e r s y s t e m o f t h e r a i n b o w t r o u t . K i r s c h n e r ( 1 9 7 0 ) , p r e s u m a b l y r e f e r r i n g t o t h e work o f K e r s t e t t e r et. j a l . ( 1 9 7 0 ) , h a s r e c e n t l y c l a i m e d t h a t e x c h a n g e d i f f u s i o n o f s o d i u m d o e s e x i s t i n Salmo g a i r d n e r i g i l l s . S u c h a c o n c l u s i o n seems v e r y p r o b a b l e , b u t p r e m a t u r e u n t i l t h e p r o b l e m o f b a c k - t r a n s p o r t i s s o l v e d . The c o n c e i v a b l e o p e r -a t i o n o f t h i s m e c h a n i s m i n t h e b r a n c h i a l e p i t h e l i u m was a l s o d i s c u s s e d i n S e c t i o n I . M o r r i s and B u l l ( 1 9 6 8 , 1970) f o r t h e ammocoete, L a m p e t r a p l a n e r i , and i n a somewhat c i r c u i t o u s f a s h i o n , B r y a n (1960) f o r t h e c r a y f i s h , A s t a c u s f l u v i a t i l i s , h a v e a r g u e d t h a t f l u x l i n k a g e s s i m i l a r t o t h o s e o f t h e 140 T a b l e X I V . C a l c u l a t e d c o n t r i b u t i o n o f d i f f e r e n t m e c h a n i s m s t o t o t a l b r a n c h i a l s o d i u m e x c h a n g e i n u r i n a r y b l o c k a g e t r o u t a s s u m i n g a l l i n f l u x - e f f l u x l i n k a g e t o be c a u s e d b y e x c h a n g e d i f f u s i o n . E x t e r n a l s o d i u m c o n c e n t r a t i o n e q u a l s 1.50 u g / m l . I n f l u x E x c h a n g e d i f f u s i o n = + 14.3 ug/100 g / m i n u t e A c t i v e t r a n s p o r t = + 4.2 " T o t a l i n f l u x = + 18.5 " E f f l u x E x c h a n g e d i f f u s i o n = - 14.3 S i m p l e d i f f u s i o n = - 2.3 T o t a l e f f l u x = - 16.6 N e t f l u x + 1.9 it 141 p r e s e n t s t u d y were c a u s e d b y an u n s a t u r a t e d c a r r i e r b a c k -t r a n s p o r t i n g s o d i u m i o n s l e a v i n g b y s i m p l e d i f f u s i o n . A t h i g h e x t e r n a l s o d i u m l e v e l s , more o f t h e c a r r i e r w o u l d be b o u n d up a c t i v e l y t r a n s p o r t i n g e x t e r n a l i o n s , and t h e m e a s u r e d e f f l u x ( b y s i m p l e d i f f u s i o n ) w o u l d be augm e n t e d . S u c h a s y s t e m demands t h a t o u t w a r d d i f f u s i o n o c c u r i n s e r i e s w i t h t h e a c t i v e s o d i u m pump ( K i r s c h n e r , 1 9 5 5 ) . I n t h e t e l e o s t , t h i s i s p r o b a b l y n o t t r u e , f o r most o f t h e p a s s i v e l e a k a g e i s t h o u g h t t o t a k e p l a c e t h r o u g h t h e t h i n w a l l e d r e s p i r a t o r y , l a m e l l a e w h i l e a c t i v e u p t a k e a p p a r a t u s i s s i t u a t e d i n t h e i n t e r l a m e l l a e f i l a m e n t a l e p i t h e l i u m ( C o n t e , 1 9 6 9 ) . T h u s i t seems l i k e l y t h a t b a c k -t r a n s p o r t c o u l d o f f e r o n l y a m i n i m a l c o n t r i b u t i o n t o t h e o b -s e r v e d c o n c e n t r a t i o n d e p e n d e n c e o f e f f l u x . However, d e f i n i t i v e s t a t e m e n t s a b o u t t h e r e l a t i v e r o l e s o f e x c h a n g e d i f f u s i o n a nd b a c k - t r a n s p o r t i n s o d i u m f l u x l i n k a g e s a c r o s s Salmo g a i r d n e r i g i l l s c a n n o t be made f r o m t h e r e s u l t o f e i t h e r t h e p r e s e n t s t u d y o r t h a t o f K e r s t e t t e r e t a l _ . ( 1 9 7 0 ) . S u c h a s s e s s m e n t s must a w a i t t h e r e s u l t s o f e x p e r i m e n t s i n w h i c h s o d i u m e f f l u x t o a s o d i u m f r e e s o l u t i o n i s m e a s u r e d d u r i n g i n h i b i t i o n o f a c t i v e t r a n s p o r t . T he u t i l i t y o f a b a c k - t r a n s p o r t m e c h a n i s m f o r an o r g a n i s m i n h a b i t i n g an e n v i r o n m e n t where s o d i u m i s e x t r e m e l y s c a r c e i s c l e a r ; h o w e v e r t h e a d v a n t a g e o f an e x c h a n g e d i f f u s i o n s y s t e m i n s u c h a s i t u a t i o n i s n o t i m m e d i a t e l y " o b v i o u s . I t c o u l d i n f a c t m e r e l y r e p r e s e n t t h e r e m n a n t i n f r e s h w a t e r o f t h e e x c h a n g e d i f f u s i o n p r o c e s s c h a r a c t e r i s t i c o f t h e s e a w a t e r a d a p t e d f o r m s o f many e u r y h a l i n e t e l e o s t s ( M o t a i s &t a l . , 1966; M o t a i s , 1 9 6 7 ) w h i c h i s i m p o r t a n t i n a d a p t a t i o n t o l o w e r s a l i n i t i e s . S u c h a m e c h a n i s m , as p r o p o s e d b y M o t a i s et- a l . (1966) o r g a n i z e s t h e i n h e r e n t " l e a k i n e s s " o f t h e g i l l s s o t h a t e f f l u x may be i n s t a n t a n e o u s l y l o w e r e d b y r e d u c t i o n o f t h e e x t e r n a l s o d i u m c o n c e n t r a t i o n , t h e r e b y p r e v e n t i n g e x c e s s i v e s a l t l o s s on e n t r y i n t o a more d i l u t e medium. T h i s s y s t e m c o u l d p r e s u m a b l y c o n t i n u e t o be b e n e f i c i a l d u r i n g a d a p t a t i o n t o f r e s h w a t e r e n v i r o n m e n t s i n w h i c h s o d i u m i s e x t r e m e l y s c a r c e . However one may a l s o s p e c u l a t e t h a t i f t h e a c t i v e u p t a k e o f e x t e r n a l s o d i u m i o n s a c r o s s t h e t r o u t g i l l o c c u r s t h r o u g h a c o u p l e d e x c h a n g e t o h y d r o g e n i o n s , f o r w h i c h K e r s t e t t e r e t a l . (19 70) h a v e p r o v i d e d some e v i d e n c e , t h e n t h e p r e s e n c e o f e x c h a n g e d i f f u s i o n may p l a y some r o l e i n r e g u l a t i o n o f a c i d -b a s e b a l a n c e . I m a g i n i n g a m e c h a n i s m s i m i l a r t o t h a t o r i g i n -a l l y p r o p o s e d f o r t h e f r o g s k i n ( U s s i n g , 1 9 4 9 b ) , w h ere e x t e r n a l s o d i u m i o n s c a n e x c h a n g e , t h r o u g h t h e m e d i a t i o n o f a c a r r i e r , w i t h e i t h e r i n t e r n a l s o d i u m i o n s (no n e t t r a n s p o r t ) o r h y d r o g e n i o n s ( n e t t r a n s p o r t ) , t h e n t h e e x i s t e n c e o f e x c h a n g e d i f f u s i o n w o u l d a l l o w t h e t r o u t t o k e e p a l a r g e number o f c a r r i e r s i t e s a v a i l a b l e f o r e x c r e t i o n o f p r o t o n s d u r i n g a c u t e l y a c i d o t i c c o n d i t i o n s . U n d e r n o r m a l c i r c u m s t a n c e s t h e s y s t e m w o u l d e f f e c t m o s t l y s o d i u m - s o d i u m e x c h a n g e s w h i c h w o u l d e n t a i l o n l y a m i n i m a l m a i n t e n a n c e c o s t o f t h e c a r r i e r and o f f e r no osmo-r e g u l a t o r y d i s a d v a n t a g e t o t h e a n i m a l . 143 SUMMARY I I 1. B r a n c h i a l s o d i u m u p t a k e r e m a i n e d c o n s t a n t d u r i n g swimming p e r i o d s o f up t o 8 h o u r s and d u r i n g r e c o v e r y f r o m e x t e n d e d e x e r c i s e . 2. Whole o r g a n i s m s o d i u m e f f l u x r a t e was h i g h e s t d u r i n g t h e . f i r s t h o u r o f e x e r c i s e i n t r o u t w h i c h were n o t u r i n a r y l i g a t e d . U n i d i r e c t i o n a l o u t w a r d movements d e c l i n e d d u r i n g t h e s e c o n d h o u r o f swimming, an d r e a c h e d l e v e l s l o w e r t h a n i n f l u x r a t e d u r i n g t h e t h i r d and s u b s e q u e n t h o u r s o f swimming. T h i s e v i d e n c e was i n d i c a t i v e o f a c o m p e n s a t o r y m e c h a n i s m i m p l e m e n t e d d u r i n g e x e r c i s e t o r e d u c e t h e o s m o t i c p e n a l t y o f a c t i v i t y . 3. E f f l u x r a t e d e m o n s t r a t e d a f u r t h e r r e d u c t i o n d u r i n g t h e s e c o n d h o u r o f r e c o v e r y a f t e r w h i c h i t i n c r e a s e d s l i g h t l y t o a l e v e l s l i g h t l y b e l o w i n f l u x r a t e . 4. A l t e r a t i o n s i n w h o l e b o d y s o d i u m n e t f l u x r a t e s o f t h e n o n -o c c l u d e d s e t s o f f i s h p a r a l l e l e d c h a n g e s i n e f f l u x r a t e u n d e r d i f f e r e n t e x e r c i s e c o n d i t i o n s . 5. T h e e f f l u x r a t e ( b r a n c h i a l ) o f t h e u r i n a r y b l o c k a g e t r e a t m e n t g r o u p was u n a f f e c t e d b y t h e e x e r c i s e c o n d i t i o n o f t h e a n i m a l . However, s u b t r a c t i o n o f t h e mean e f f l u x r a t e s o f t h i s g r o u p f r o m t h a t o f t h e shams y i e l d e d u n r e a l i s t i c a l l y h i g h v a l u e s f o r r e n a l s o d i u m e f f l u x r a t e s d u r i n g a c t i v i t y . F u r t h e r e v i d e n c e was p r e s e n t e d w h i c h s u g g e s t e d t h a t t h e b r a n c h i a l s o d i u m l o s s e s o f t h e l i g a t e d t r o u t were a b n o r m a l l y d e p r e s s e d due t o t h e e f f e c t o f r e n a l o c c l u s i o n . 6. C o n s e q u e n t l y , most o f t h e v a r i a t i o n i n w h o l e a n i m a l e f f l u x r a t e s w i t h d i f f e r e n t e x e r c i s e c o n d i t i o n s o f t h e u n l i g a t e d f i s h 144 h a s b e e n a t t r i b u t e d t o a b r a n c h i a l s o u r c e . 7. B r a n c h i a l s o d i u m i n f l u x r a t e was u n a f f e c t e d b y u r i n a r y c a t h e t e r i z a t i o n o r b l o c k a g e . 8. Whole o r g a n i s m e f f l u x r a t e was s l i g h t l y e l e v a t e d i n t r o u t b e a r i n g o p e n u r i n a r y c a t h e t e r s (shams) r e l a t i v e t o t h a t o f n o r m a l f i s h . However t h e two g r o u p s e x h i b i t e d v e r y s i m i l a r r e s p o n s e s i n e f f l u x r a t e u n d e r v a r i o u s e x e r c i s e s i t u a t i o n s . 9. The h i g h e r e f f l u x r a t e s o f t h e shams was r e f l e c t e d i n s i g -n i f i c a n t l y l o w e r t o t a l i n t e r n a l e x c h a n g e a b l e s o d i u m c o n t e n t s . T h i s e f f e c t may be a s c r i b e d t o e l e v a t i o n o f b o t h b r a n c h i a l a n d r e n a l l o s s e s f o l l o w i n g c a n n u l a t i o n . 10. U r i n a r y l i g a t e d a n i m a l s s u f f e r e d a p r o n o u n c e d n e t g a i n o f w a t e r o v e r t h e e x p e r i m e n t a l p e r i o d a c c o m p a n i e d b y s i g n i f i c a n t i n c r e a s e s i n r a d i o s o d i u m s p a c e and t i s s u e w a t e r l e v e l s , a n d a d e c r e a s e i n p l a s m a s o d i u m c o n c e n t r a t i o n s . P l a s m a w a t e r l e v e l s a n d h e m a t o c r i t , h o w e v e r , d i d n o t c h a n g e m a r k e d l y . T h e s e e f f e c t s were i n t e r p r e t e d i n t e r m s o f t h e r e l e g a t i o n o f e x c e s s w a t e r t o t h e e x t r a v a s c u l a r s p a c e w h i c h p r e v e n t e d a l a r g e i n c r e a s e o f p l a s m a v o l u m e ; t h i s w a t e r s h i f t was a p p a r e n t l y a c c o m p a n i e d b y a n e t movement o f s o d i u m f r o m t h e p l a s m a i n t o t h e e x t r a - c e l l u l a r b u t e x t r a - v a s c u l a r c o m p a r t m e n t . The r e d u c t i o n o f p l a s m a s o d i u m l e v e l s may h a v e b e e n r e s p o n s i b l e f o r t h e p o s t u l a t e d d e p r e s s i o n o f b r a n c h i a l s o d i u m e f f l u x r a t e s i n r e n a l b l o c k a g e f i s h . 1 1 . B r a n c h i a l s o d i u m i n f l u x r a t e was a f f e c t e d b y e x t e r n a l s o d i u m l e v e l s . T h i s c o n c e n t r a t i o n d e p e n d e n c e was w e l l d e s -c r i b e d b y t h e K i r s c h n e r (1955) e q u a t i o n ( a n a l o g o u s t o t h e M i c h a e l i s - M e n t e n e q u a t i o n ) w i t h Ks = .014 mEq/L an d F i max = 58.40 uEq/100 g / h o u r . T h e s e v a l u e s were i n d i c a t i v e o f an 145 e x t r e m e l y e f f i c i e n t s y s t e m f o r s o d i u m u p t a k e f r o m d i l u t e s o l u t i o n s i n t h e r a i n b o w t r o u t . 1 2 . B r a n c h i a l s o d i u m e f f l u x r a t e s , as d e t e r m i n e d f r o m t h e u r i n a r y o c c l u s i o n g r o u p a l o n e , w e r e a l s o d e p e n d e n t on e x t e r n a l s o d i u m l e v e l s . T h i s phenomenon was c o n s i d e r e d i n d i c a t i v e , a l t h o u g h n o t c o n c l u s i v e , o f t h e p r e s e n c e o f an e x c h a n g e d i f -f u s i o n m e c h a n i s m f o r s o d i u m i n t h e g i l l s o f f r e s h w a t e r a d a p t e d Salmo g a i r d n e r i . SECTION I I I THE E F F E C T OF E X E R C I S E ON WATER BALANCE INTRODUCTION I I I The e x p e r i m e n t s o f t h e f i r s t two s e c t i o n s were d e s i g n e d t o a s s e s s t h e e f f e c t o n s o d i u m b a l a n c e i n g e n e r a l , and s o d i u m f l u x e s a c r o s s t h e g i l l s i n p a r t i c u l a r , o f s h i f t s i n t h e b r a n c h -i a l r e s p i r a t o r y / o s m o r e g u l a t o r y c o m p r o m i s e c a u s e d b y t h e p a r t -i c u l a r m e t a b o l i c demands o f e x e r c i s e . The p r e s e n t s t u d y was d e s i g n e d as a c o m p l e m e n t a r y i n v e s t i g a t i o n o f w a t e r f l u x a n d r e g u l a t i o n d u r i n g a c t i v i t y . B e c a u s e t h e n e c e s s a r y e x p e r i -m e n t a l f a c i l i t i e s w ere a v a i l a b l e f o r o n l y a s h o r t p e r i o d o f t i m e , t h e work was somewhat p r e l i m i n a r y i n n a t u r e a n d i n v o l v e d o n l y a s m a l l number o f a n i m a l s , b u t y i e l d e d a g o o d d e a l o f u s e f u l i n f o r m a t i o n . As t h e e f f e c t s on s o d i u m b a l a n c e o f a l t e r a t i o n s i n b r a n c h i a l b l o o d f l o w a n d d i s t r i b u t i o n c o u l d be m a n i f e s t e d i n b o t h c a r r i e r m e d i a t e d and s i m p l e d i f f u s i o n a l f l u x e s , i t h a d p r e v i o u s l y b e e n d e s i r a b l e t o s e p a r a t e t h e u n i d i r e c t i o n a l c o m p o n e n t s o f n e t f l u x . The s m a l l v o l u m e s y s t e m n e c e s s i t a t e d ' b y t h i s p u r p o s e h a d n o t p e r m i t t e d t h e i m p o s i t i o n o f s t a n d a r d swimming c o n d i t i o n s o r any d i r e c t m e a s u r e m e n t o f t h e r e s p i r -a t o r y c h a n g e s o c c u r r i n g d u r i n g e x e r c i s e . However, i t i s e x t r e m e l y u n l i k e l y t h a t any c a r r i e r m e d i a t e d p r o c e s s e s a r e 147 d i r e c t l y i n v o l v e d i n w a t e r e x c h a n g e a t t h e g i l l s . C o n s e q u e n t l y d e t e r m i n a t i o n o f t h e n e t f l u x o f w a t e r a l o n e s h o u l d p r o v i d e a d e q u a t e m e a s u r e o f t h e e f f e c t i v e b r a n c h i a l p e r m e a b i l i t y t o t h i s s u b s t a n c e a t a p a r t i c u l a r t i m e . I n f r e s h w a t e r t e l e o s t s , w a t e r g a i n e d f r o m t h e e n v i r o n -ment e n t e r s a c r o s s t h e g i l l s and t h e i n t e s t i n e ( E v a n s , 1 9 6 7 ; P o t t s a n d E v a n s , 1 9 6 7 ) , t h e s k i n b e i n g i m p e r m e a b l e , ( B e n t l e y , 1962; Fromm,1968), and i s e l i m i n a t e d t h r o u g h a s i n g l e p a t h w a y , t h e k i d n e y . T h u s i f t h e a s s u m p t i o n i s t a k e n t h a t t h e a n i m a l m a i n t a i n s a s t e a d y s t a t e , t h e u r i n e f l o w s h o u l d be e q u i v a l e n t t o n e t w a t e r f l u x . T h e r a i n b o w t r o u t d o e s n o t d r i n k i n f r e s h w a t e r ( S h e h a d e h an d G o r d o n , 1 9 6 9 ) f u r t h e r s i m p l i f y i n g t h e s i t u a t i o n s o t h a t u r i n e f l o w e q u a l s n e t b r a n c h i a l w a t e r e n t r y i n t h i s s p e c i e s . C o n s e q u e n t l y , c o l l e c t i o n o f u r i n e a f f o r d s e s t i m a t e s o f b r a n c h i a l p e r m e a b i l i t y w i t h o u t a c c o m p a n y i n g l i m i t a t i o n o f t h e v o l u m e o f t h e e x p e r i m e n t a l s y s t e m . Use o f t h i s t e c h n i q u e i n t h e p r e s e n t s t u d y a l l o w e d s i m u l t a n e o u s d e t e r -m i n a t i o n s o f o x y g e n c o n s u m p t i o n an d n e t b r a n c h i a l w a t e r e n t r y u n d e r c o n t r o l l e d e x e r c i s e c o n d i t i o n s i n a swimming r e s p i r o m e t e r ( B r e t t , 1964; S t e v e n s , 1 9 6 8 b ) . I t was h o p e d t h a t s u c h d a t a w o u l d p r o v i d e a q u a n t i t a t i v e r e l a t i o n s h i p b e t w e e n g a s and w a t e r e x c h a n g e an d f u r t h e r i n f o r m a t i o n a b o u t t h e c o m p e n s a t o r y l i m i t -a t i o n s i n b r a n c h i a l h y d r o m i n e r a l p e r m e a b i l i t y w h i c h i n S e c t i o n I I w ere p o s t u l a t e d t o o c c u r d u r i n g p r o l o n g e d e x e r c i s e . I n o r d e r t o f u r t h e r p u r s u e t h e q u e s t i o n o f a c o m p e n s a t o r y r e d u c t i o n i n g i l l p e r m e a b i l i t y , w e i g h t c h a n g e s a t d i f f e r e n t swimming d u r a t i o n s were d e t e r m i n e d as m e a s u r e s o f w a t e r r e g u l -a t i o n . The d a t a o b t a i n e d a l s o p r o v i d e d e x p l a n a t i o n f o r t h e d e c r e a s e i n b l o o d v o l u m e and i n c r e a s e i n p l a s m a s o d i u m l e v e l s 148 m e a s u r e d d u r i n g a c t i v i t y i n S e c t i o n I . I n a d d i t i o n t o r e l a t i n g w a t e r and g a s f l u x e s , t h e c o l l e c t i o n o f u r i n e a l l o w e d d i r e c t m e n s u r a t i o n o f u r i n a r y s o d i u m e f f l u x r a t e . The r e s u l t s a i d e d i n t e r p r e t a t i o n o f t h e d a t a o f S e c t i o n I I and h a v e a l r e a d y b e e n n o t e d . i n b r i e f summary ( T a b l e X I ) . A f a i r l y e x t e n s i v e c a t i o n a n a l y s i s ( N a + , K + , M g + * C a + + ) o f t h e c o l l e c t e d s a m p l e s p r o v i d e d f u r t h e r i n f o r m a t i o n on k i d n e y f u n c t i o n d u r i n g e x e r c i s e . U r i n e f l o w s a n d r e n a l i o n l o s s e s h a v e n o t p r e v i o u s l y b e e n m e a s u r e d i n any f r e s h w a t e r t e l e o s t s u n d e r c o n t r o l l e d swimming c o n d i t i o n s . T h u s d e t e r m i n a t i o n o f w a t e r f l u x e s t h r o u g h c o l l e c t i o n o f u r i n e p r o v i d e d an o p p o r t u n i t y f o r e x a m i n i n g some c h a r a c t e r -i s t i c s o f t h e r e s p i r a t o r y / h y d r o e l e c t r o l y t i c a d j u s t m e n t w h i c h t h e u s e o f s o d i u m e x c h a n g e as t h e t h e o s m o r e g u l a t o r y v a r i a b l e h a d p r e v i o u s l y p r e c l u d e d . F u r t h e r m o r e t h e i n v e s t i g a t i o n s e r v e d t o s o l v e s e v e r a l p r o b l e m s r a i s e d b y t h e r e s u l t s o f t h e f i r s t two s e c t i o n s , a n d p r o v i d e d i n f o r m a t i o n o n r e n a l p h y s i o l o g y d u r i n g swimming. 149 METHODS I I I E x p e r i m e n t a l A n i m a l s E x p e r i m e n t s were p e r f o r m e d on s e x u a l l y i m m a t u r e r a i n -bow t r o u t ( S a l m o g a i r d n e r i ) w i t h w e i g h t s r a n g i n g f r o m 90 t o 180 g . The a n i m a l s were k e p t i n d o o r s f o r a t l e a s t 3 weeks p r i o r t o e x p e r i m e n t a t i o n i n a 250 g a l l o n c o n c r e t e h o l d i n g t a n k s u p p l i e d w i t h f u l l y o x y g e n a t e d f r e s h w a t e r a t 7 - 8 ° C ; d u r i n g t h i s t i m e , t h e y were f e d r e g u l a r l y w i t h a c o m m e r c i a l t r o u t p e l l e t . A l l e x p e r i m e n t s w e r e c a r r i e d o u t a t t h e V a n c o u v e r P u b l i c A q u a r i u m d u r i n g F e b r u a r y and M a r c h , 19 70. I . U r i n e F l o w v e r s u s O x y gen C o n s u m p t i o n E x p e r i m e n t s 1. O p e r a t i n g P r o c e d u r e and C a n n u l a t i o n s I m p l a n t a t i o n o f u r i n a r y c a t h e t e r s was p e r f o r m e d as d e s c r i b e d i n S e c t i o n I on t r o u t a n a e s t h e t i z e d i n a 1/10,000 MS 222 s o l u t i o n a t 7 - 1 0 ° C . The h i g h e r MS 222 c o n c e n t r a t i o n was n e c e s s i t a t e d b y t h e c o l d e r w a t e r t e m p e r a t u r e . C a n n u l a e ( l e n g t h = 45 cm) were c o n s t r u c t e d f r o m PE 60 a n d PE 190 t u b i n g as i n S e c t i o n I . However, b e c a u s e o f t h e l o w b o d y w e i g h t s and s e x u a l i m m a t u r i t y o f t h e s e f i s h , t h e u r o g e n i t a l p a p i l l a e w e r e e x t r e m e l y s m a l l . T h i s f a c t n e c e s s i t a t e d a r e d u c t i o n i n l e n g t h o f t h e p r o x i m a l t i p and i n d i a m e t e r o f t h e f l a n g e s o f t h e c a t h e t e r . D e s p i t e t h e s e m o d i f i c a t i o n s , many c a n n u l a t i o n a t t e m p t s f a i l e d ; o f t h e 18 a n i m a l s o r i g i n a l l y c a t h e t e r i z e d , o n l y 5 e x h i b i t e d b o t h p a t e n t a n d f r e e - d r a i n i n g c a n n u l a e . F o l l o w i n g c o m p l e t i o n o f t h e o p e r a t i o n , t h e f i s h was s e a l e d i n t o a m e t a b o l i s m b o x w h i l e s t i l l a n a e s t h e t i z e d . 150 R e c o v e r y was a i d e d b y d i r e c t i n g a w a t e r -flow o f 300 m l / m i n . t h r o u g h t h e c hamber. 2. E x p e r i m e n t a l S y s t e m U r i n e p r o d u c t i o n and o x y g e n c o n s u m p t i o n w e r e s i m u l t -a n e o u s l y d e t e r m i n e d d u r i n g r e s t i n m e t a b o l i s m b o x e s (5 f i s h ) a n d t h e n d u r i n g c o n t r o l l e d l e v e l s o f swimming a c t i v i t y (4 f i s h ) . U r i n e s a m p l e s w e r e c o l l e c t e d f o r l a t e r i o n i c a n a l y s i s . T e r m i n a l w e i g h i n g a n d m e a s u r i n g was c a r r i e d o u t as i n S e c t i o n I . ( a ) , M e t a b o l i s m B o x e s R e s t i n g s t a t e m e a s u r e m e n t s w e r e t a k e n f r o m t r o u t s e a l e d i n b l a c k e n e d p l e x i g l a s s m e t a b o l i s m c h a m b e r s ( l e n g t h = 43.1 cm; w i d t h - 8.6 cm; d e p t h = 8.2 cm) c o n t i n u a l l y f l u s h e d w i t h f r e s h w a t e r a t 7 - 8 ° C . A m o v e a b l e p a r t i t i o n i n t h e b o x e s p e r m i t t e d r e s t r i c t e d movements, b u t d i d n o t a l l o w t h e f i s h t o c h a n g e p o s i t i o n . O p e r c u l a r r a t e s c o u l d be v i s u a l l y c o u n t e d w i t h t h e a i d o f m i r r o r s p l a c e d b e n e a t h t h e c h a m b e r s . The u r i n a r y c a t h e t e r was l e d o u t o f t h e b o x v i a a t t a c h m e n t t o a #21 n e e d l e p i e r c i n g a r u b b e r s t o p p e r i n t h e r e a r o f t h e c h a m b e r . The c a t h e t e r d r a i n e d b y g r a v i t y . The w i t h d r a w a l o f i n c u r r e n t a n d e x c u r r e n t w a t e r s a m p l e s and m e a s u r e m e n t o f w a t e r f l o w r a t e (80 - 200 m l /min) t h r o u g h t h e chamber p e r m i t t e d o x y g e n c o n s u m p t i o n d e t e r m i n a t i o n s . R e p r e s e n t a t i v e e f f l u e n t s a m p l e s were e n s u r e d b y m i x i n g c h a m b e r s a t t h e r e a r o f e a c h b o x . P a r t i a l p r e s s u r e o f o x y g e n ( P 0 2 ' s ) i n w a t e r were d e t e r -m i n e d w i t h a t h e r m o s t a t t e d o x y g e n m i c r o - e l e c t r o d e s y s t e m ( R a d i o m e t e r - C o p e n h a g e n ) ; c o n v e r s i o n o f d i f f e r e n t i a l P 0 2 * s t o d i f f e r e n t i a l o x y g e n c o n t e n t s b y means o f t e m p e r a t u r e d e p e n d e n t 151 s o l u b i l i t y f a c t o r s a l l o w e d c a l c u l a t i o n o f o x y g e n c o n s u m p t i o n r a t e s . (b) R e s p i r o m e t e r D a t a a t v a r i o u s l e v e l s o f swimming a c t i v i t y w ere t a k e n f r o m t r o u t e x e r c i s e d a t 7 - 9 ° C . i n t h e swimming r e s p i r o m e t e r o r i g i n a l l y u s e d b y S t e v e n s (1968 a). The d e s i g n was s i m i l a r t o t h a t d e s c r i b e d b y B r e t t (1964) ( F i g . 2 3 ) . I n b r i e f , t h e r e s p -i r o m e t e r c o n s i s t e d o f a p l e x i g l a s s t u b e ( l e n g t h = 70 cm; i n s i d e d i a m e t e r = 13 cm) t h r o u g h w h i c h w a t e r c o u l d be r e c i r c u l -a t e d a t a r a n g e o f v e l o c i t i e s . A v a r i a b l e s p e e d e l e c t r i c m o t o r p r o p e l l e d t h e pump, a l l o w i n g c o n t i n u o u s v a r i a t i o n o f s p e e d f r o m 0 t o 45.7 c m / s e c . The v o l u m e o f t h e s y s t e m was 2 3.75 L . The r e s p i r o m e t e r c o u l d be e i t h e r c o n t i n u a l l y f l u s h e d w i t h f r e s h w a t e r o r s e a l e d f o r measu r e m e n t o f o x y g e n consump-t i o n s . I n t h e l a t t e r c a s e , a s m a l l h e a d e r t a n k c o n n e c t i n g t o t h e chamber p r e v e n t e d b u b b l e f o r m a t i o n when w a t e r s a m p l e s were w i t h d r a w n . The a n t e r i o r two t h i r d s o f t h e swimming t u b e were c o v e r e d w i t h b l a c k p l a s t i c ; t r o u t g e n e r a l l y o r i e n t e d u n d e r t h e p o s t e r i o r e n d o f t h e p l a s t i c , u s i n g i t a s a v i s u a l c u e t o m a i n t a i n p o s i t i o n d u r i n g e x e r c i s e . A m e t a l g r i d a t t h e r e a r o f t h e r e s p i r o m e t e r c o u l d be e l e c t r i f i e d a t a l o w v o l t a g e t o e n c o u r a g e swimming p e r f o r m a n c e . The u r i n a r y c a t h e t e r was e x t e n d e d w i t h a f u r t h e r 20 cm o f PE 60 and b r o u g h t o u t t h r o u g h t h e t o p o f t h e chamber v i a a #21 n e e d l e t h r o u g h a r u b b e r s t o p p e r ; i n t h i s s y s t e m , t h e c a n n u l a d r a i n e d b y s i p h o n . ( c ) E x p e r i m e n t a l P r o c e d u r e s ( i ) R e s t i n g T r o u t . C a t h e t e r i z e d f i s h w ere m a i n t a i n e d i n m e t a b o l i s m c h a m b e r s f o r up t o 8 d a y s a f t e r o p e r a t i o n . D u r i n g t h e f i r s t 4 d a y s , u r i n e was c o l l e c t e d f r o m 5 f i s h a s 24 152 F i g u r e 23 A d i a g r a m o f t h e swimming r e s p i r o m e t e r u s e d i n t h e e x p e r i m e n t s o f S e c t i o n I I I . water inflow header tank water sampling p u r i n e collection water overflow black plastic f ^•chargeable grid variable speed electric m o t o r ^ pump 153 h o u r s a m p l e s . Oxygen c o n s u m p t i o n a n d o p e r c u l a r r a t e s w e r e a s c e r t a i n e d p e r i o d i c a l l y on a f u r t h e r 3 t r o u t d u r i n g t h e f i r s t 48 - 60 h o u r s a f t e r c a n n u l a t i o n . U n f o r t u n a t e l y , t h e u r i n a r y c a t h e t e r s were n o t p a t e n t on t h e l a t t e r a n i m a l s a n d u r i n e p r o -d u c t i o n c o u l d n o t be q u a n t i f i e d . On t h e f i f t h p o s t - o p e r a t i v e d a y , t h e u r i n e p r o d u c t i o n o f e a c h f i s h was m e a s u r e d o v e r a 5 h o u r p e r i o d d u r i n g w h i c h a t l e a s t 5 d e t e r m i n a t i o n s o f m e t a -b o l i c r a t e were c a r r i e d o u t . ( i i ) Swimming T r o u t . B e t w e e n t h e 5 t h a n d 8 t h p o s t -o p e r a t i v e d a y s , a f i s h was g e n t l y t r a n s f e r r e d , w i t h o u t a n a e s -t h e s i a , t o t h e swimming r e s p i r o m e t e r a n d l e f t o v e r n i g h t t o a c c u s t o m i t s e l f t o t h e c h a m b e r . D u r i n g t h i s t i m e , t h e r e s p i r o -m e t e r was f l u s h e d w i t h f r e s h w a t e r a t a v e l o c i t y o f 10.7 c m / s e c , t h e minimum c u r r e n t i n t o w h i c h t h e t r o u t w o u l d c o n t i n u o u s l y o r i e n t w i t h o u t swimming. The u r i n a r y c a t h e t e r was l e d o u t o f t h e chamber and a l l o w e d t o d r a i n f o r a t l e a s t 2 h o u r s b e f o r e t h e s t a r t o f an e x p e r i m e n t . T r o u t were t h e n s u b j e c t e d t o t h e f o l l o w i n g r e g i m e : 10.7 c m / s e c . - 3 h o u r s 21.4 c m / s e c . - 3 h o u r s 10.7 c m / s e c . - 3 h o u r s 21.4 c m / s e c . - 15 m i n u t e s 32.1 c m / s e c . - 3 h o u r s 10.7 c m / s e c . - 3 h o u r s 21.4 c m / s e c . - 15 m i n u t e s 32.1 c m / s e c . - 15 m i n u t e s 42.8 c m / s e c . - • 3 h o u r s 10.7 c m / s e c . - 3 h o u r s F o r one f i s h ( # 5 9 ) , t h e swimming r e g i m e was i n t e r r u p t e d f o r l e n g t h y b r e a k s n e a r t h e b e g i n n i n g a n d e n d o f t h e e x p e r i m e n t . However, as p o s s i b l e s h i f t s i n t h e b a s e l i n e r a t e o f u r i n e p r o d u c t i o n o c c u r r e d d u r i n g t h e s e i n t e r v a l s , p e r i o d s o f t h e swimming r e g i m e were i m p o s e d c o n s e c u t i v e l y on e a c h o f t h e o t h e r 154 3 a n i m a l s t e s t e d (#55, #63, #65) d u r i n g a c o n t i n u o u s e x p e r i -m e n t a l p e r i o d o f 21.75 h o u r s . T o t a l u r i n e p r o d u c t i o n was c o l l e c t e d a n d m e a s u r e d f o r e a c h 60 m i n u t e s e c t i o n o f t h e 3 h o u r t r e a t m e n t p e r i o d s , a n d d u r i n g t h e 15 m i n u t e i n t e r m e d i a t e p e r i o d s . O x y gen c o n s u m p t i o n was a l s o d e t e r m i n e d o v e r e a c h o f t h e one h o u r i n t e r v a l s b y s e a l i n g t h e r e s p i r o m e t e r f o r a l e n g t h o f t i m e s u f f i c i e n t f o r t h e o r g a n i s m t o r e d u c e t h e P 0 2 i n t h e chamber b y 10 - 1 5 % (30 - 55 m i n u t e s ) . A t no t i m e was t h e P 0 2 i n t h e r e s p i r o m e t e r p e r m i t t e d t o f a l l b e l o w 120 mm Hg. PO ? a n a l y s e s on d u p l i c a t e w a t e r s a m p l e s drawn a t t h e b e g i n n i n g a n d e n d o f e a c h c l o s u r e p e r i o d a l l o w e d c a l c u l a t i o n o f m e t a b o l i c r a t e s . O x y gen up-t a k e s d u r i n g t h e 15 m i n u t e s v e l o c i t y i n c r e m e n t p e r i o d s w e r e n o t g r e a t e n o u g h t o q u a n t i f y a c c u r a t e l y . O p e r c u l a r r a t e s a n d t a i l b e a t f r e q u e n c i e s w e r e c o u n t e d r e g u l a r l y t h r o u g h o u t t h e e x p e r i m e n t s w i t h t h e a i d o f m i r r o r s p l a c e d u n d e r t h e r e s p i r o -m e t e r . 3. A n a l y t i c a l P r o c e d u r e s U r i n e s a m p l e s w e r e c o l l e c t e d i n s m a l l p o l y e t h y l e n e v i a l s , m e a s u r e d w i t h a H a m i l t o n s y r i n g e , a n d t h e n f r o z e n i n t h e v i a l s a t - 1 2 ° C . f o r l a t e r i o n i c a n a l y s e s . A l l a s s a y s w e r e p e r f o r m e d i n d u p l i c a t e a g a i n s t c a l i b r a t i o n c u r v e s c o n s t r u c t e d w i t h a p p r o p r i a t e d i l u t i o n s o f c o m m e r c i a l l y p r e p a r e d s t a n d a r d s ( H a r l e c o ) ; t h e T e c h t r o n M o d e l AA 120 A t o m i c A b s o r p t i o n S p e c t r o p h o t o m e t e r was u s e d f o r a l l d e t e r m i n a t i o n s . ( i ) S o d i u m i n U r i n e . A l i q u o t s o f e a c h s a m p l e were d i l u t e d 1/600 w i t h d i s t i l l e d w a t e r and r e a d a t 5890 8 on t h e f l a m e e m i s s i o n mode o f t h e s p e c t r o p h o t o m e t e r ( c a l i b r a t i o n r a n g e = 0 - 1.0 ug N a + / m l . ( i i ) P o t a s s i u m i n U r i n e . P o t a s s i u m c o n c e n t r a t i o n s w e r e a s c e r t a i n e d on t h e f l a m e e m i s s i o n mode o f t h e i n s t r u m e n t a t 7664 8. S a m p l e s w e r e d i l u t e d 1/250 a n d a s s a y e d a g a i n s t c a l i b r a t i o n c u r v e s i n t h e r a n g e 0 - 2 0 u E q K / L . B e c a u s e o f t h e known i n t e r f e r e n c e o f h i g h s o d i u m l e v e l s on p o t a s s i u m f l a m e e m i s s i o n , b o t h s t a n d a r d s a n d unknowns were swamped w i t h 200 ug N a + / m l . ( i i i ) C a l c i u m and M a g n e s i u m i n U r i n e . The same d i l u t i o n ( 1/60) o f e a c h s a m p l e was u t i l i z e d f o r d e t e r m i n a t i o n o f b o t h i o n s . S o d i u m a n d p o t a s s i u m h a v e b e e n shown t o , p o t e n t i a t e c a l c i u m f l a m e e m i s s i o n ( T e l o h , 1 9 5 8 ) ; t h u s unknowns an d s t a n d -a r d s were d i l u t e d w i t h b o t h a 200 ug N a + / m l swamp and a 100 ug K + / m l swamp. No c o r r e c t i o n was made f o r t h e r e p o r t e d d e p r e s s a n t e f f e c t o f p h o s p h a t e i o n on t h e s p e c t r a l e m i s s i o n o f c a l c i u m ( T e l o h , 1 9 5 8 ) . However, t e s t s r e v e a l e d t h a t a d d i t i o n s o f c o n s t a n t known amounts o f c a l c i u m ( a p p r o x i m a t e l y 30% o f t o t a l c o n c e n t r a t i o n ) t o a r a n g e o f d i f f e r e n t , b u t i d e n t i c a l l y d i l u t e d , u r i n e s a m p l e s c o u l d be r e c o v e r e d a n a l y t i c a l l y 93 -1 0 1 % . T h i s e v i d e n c e i n d i c a t e s t h a t , a f t e r N a + a n d K + swamping, o n l y m i n i m a l i n t e r f e r e n c e e f f e c t s r e m a i n e d . C a l c i u m a n a l y s e s w e r e p e r f o r m e d a t 422 7 8 o v e r a c a l i b r a t i o n r a n g e o f 0 - 100 u E q C a + + / L . The r e m a i n d e r o f e a c h d i l u t i o n was a n a l y z e d f o r mag-n e s i u m a t 2852 & on t h e a t o m i c a b s o r p t i o n mode o f t h e s p e c t r o -p h o t o m e t e r o v e r a c a l i b r a t i o n r a n g e o f 0 - 80 u E q M g + + / L . A s a. t h e unknowns h a d a l r e a d y b e e n swamped (200 ug Na / m l ; 100 u g K + / m l ) f o r c a l c i u m m e a s u r e m e n t s , t h e magnesium s t a n d a r d s were s i m i l a r l y f o r t i f i e d a s a s a f e t y p r e c a u t i o n . However, s o d i u m , 156 p o t a s s i u m , a n d p h o s p h a t e i o n a p p a r e n t l y do n o t i n t e r f e r e w i t h t h e s p e c t r a l a b s o r p t i o n o f magnesium i n u r i n e (Dawson and H e a t o n , 1 9 6 1 ) . As t h e p r i m a r y p u r p o s e o f t h i s s t u d y was t o c o r r e l a t e u r i n e v o l u m e w i t h o x y g e n u p t a k e , u r i n e was c o l l e c t e d i n h o u r l y s a m p l e s . The v o l u m e o f t h e c o l l e c t i n g d u c t s a n d u r e t e r was n e g l i g i b l e , a n d as t h e c a t h e t e r d r a i n e d b y s i p h o n , u r i n e w o u l d n o t h a v e a c c u m u l a t e d i n t h e b l a d d e r . However t h e d e p o s i t i o n i n t o t h e c o l l e c t i n g v i a l o f u r i n e f o r m e d a t any one moment was d e l a y e d b y a f a c t o r c o r r e s p o n d i n g t o t h e v o l u m e o f t h e c a t h e t e r (0.35 ml) a n d t h e r a t e o f u r i n e f l o w . T h u s an h o u r l y s a m p l e w o u l d r e p r e s e n t t h e e x a c t v o l u m e e x c r e t e d d u r i n g t h a t 60 m i n u t e p e r i o d , b u t , a t l o w u r i n e f l o w r a t e s , may h a v e b e e n p r o d u c e d 2 - 3 h o u r s p r e v i o u s l y . T h u s i t was n e c e s s a r y t o r e f e r t h e m e a s u r e d i o n i c c o m p o s i t i o n o f c o l l e c t e d u r i n e t o i t s p r o d u c t i o n t i m e i n t h e f o l l o w i n g manner. C u m u l a t i v e u r i n e v o l u m e was p l o t t e d a g a i n s t e l a p s e d t i m e . The c a n n u l a v o l u m e was g r a p h -i c a l l y s u b t r a c t e d f r o m t h e c u m u l a t i v e v o l u m e a t t h e e n d o f e a c h s a m p l e p e r i o d , a n d a p e r p e n d i c u l a r d r o p p e d t o t h e t i m e a x i s a t t h e s e p o i n t s , t h e r e b y d e f i n i n g a new s e t o f t i m e i n t e r -v a l s o v e r w h i c h e a c h u r i n e s a m p l e was f o r m e d . The m e a s u r e d i o n i c c o m p o s i t i o n o f e a c h s a m p l e was t h e n r e f e r r e d t o t h e m i d -p o i n t o f t h e s e p e r i o d s . U n f o r t u n a t e l y , t h e p r o d u c t i o n t i m e s o f c o l l e c t e d s a m p l e s o f t e n s p a n n e d two swimming s p e e d s , c r e a t i n g c o m p o s i t i o n v a l u e s r e p r e s e n t a t i v e o f n e i t h e r c o n d i t i o n . T h u s any v a r i a t i o n s i n i o n i c c o n t e n t a s s o c i a t e d w i t h d i f f e r e n t a c t i v i t y l e v e l s w o u l d h a v e b e e n somewhat dampened b y t h i s m i x i n g p r o c e s s . 157 I I . W e i g h t Change v s . Swimming D u r a t i o n E x p e r i m e n t s W e i g h t c h a n g e s w e r e m e a s u r e d as an i n d i c a t i o n o f w a t e r f l u x e s i n t r o u t swum f o r v a r i o u s l e n g t h s o f t i m e i n t h e r e s p i r o -m e t e r a t 32.1 c m / s e c . a n d i n i d e n t i c a l l y h a n d l e d s e t s o f c o n t r o l a n i m a l s . E x p e r i m e n t s were p e r f o r m e d on a b a t c h o f a p p r o x i m -a t e l y 70 t r o u t h e l d i n t h e 250 g a l l o n c o n c r e t e t a n k ; as 151 d e t e r m i n a t i o n s were made i n t h i s s t u d y , e a c h f i s h was u s e d 2 - 3 t i m e s . The a n i m a l s were s t a r v e d f o r 6 d a y s p r i o r t o e x p e r i m e n t a t i o n t o p r e v e n t f a e c a l e v a c u a t i o n c o n t r i b u t i n g t o w e i g h t c h a n g e s . W a t e r t e m p e r a t u r e t h r o u g h o u t t h e s t u d y was 7 - 8 ° C . F o r w e i g h i n g , an u n a e s t h e t i z e d t r o u t was r e m o v e d f r o m t h e w a t e r , p l a c e d on a b e d o f p a p e r t o w e l s , and g e n t l y b u t t h o r o u g h l y d r i e d f o r 15 s e c o n d s . T he a n i m a l was t h e n a d d e d t o a t a r e d c o n t a i n e r a n d w e i g h e d t o t h e n e a r e s t .05 g . The w e i g h i n g c o n t a i n e r c o n s i s t e d o f a l i g h t s t y r o f o a m chamber ( l e n g t h = 30 cm; w i d t h = 7 cm; d e p t h = 12 cm) f i t t i n g t h e s h a p e o f t h e f i s h a n d l i n e d w i t h a p l a s t i c s a c k . T he b a g c o n t a i n e d 500 ml o f w a t e r a n d was s e a l e d w i t h s t a p l e s i m m e d i a t e l y a f t e r e n t r y o f t h e f i s h . A n i m a l s r a r e l y s t r u g g l e d i n t h e a p p a r a t u s . The t r o u t was f i n a l l y r e t u r n e d t o i t s a q u a r i u m and g e n t l y r e l e a s e d u n d e r w a t e r . T o t a l w e i g h i n g t i m e was a b o u t 60 s e c o n d s . T e s t s w i t h d e a d f i s h showed t h a t t h e w e i g h i n g p r o c e d u r e was a c c u r a t e t o - 0 . 1 g . F o r w e i g h t c h a n g e m e a s u r e m e n t s , f i s h w ere t r a n s f e r r e d f r o m t h e h o l d i n g t a n k t o i n d i v i d u a l b l a c k e n e d a n d c o v e r e d a q u a r i a (5 o r 10 g a l l o n ) s e r v e d w i t h a c o n s t a n t s u p p l y o f f u l l y o x y g e n a t e d f r e s h w a t e r . T he a n i m a l s were l e f t u n d i s t u r b e d f o r a t l e a s t 8 h o u r s t o r e c o v e r f r o m t h i s i n i t i a l h a n d l i n g . 158 T h e n i n d i v i d u a l t r o u t w e r e n e t t e d f r o m t h e i r a q u a r i a , w e i g h e d , and r e t u r n e d t o t h e t a n k s f o r a f u r t h e r 8 h o u r s r e c u p e r a t i o n . A f t e r t h i s i n t e r v a l , e x p e r i m e n t a l a n i m a l s were r e m o v e d f r o m t h e i r c h a m b e r s and q u i c k l y a i r d i p p e d t o t h e r e s p i r o m e t e r (5 s e c o n d s ) . W a t e r v e l o c i t y was s e t a t 10.7 c m / s e c . (15 s e c o n d s ) , t h e n 21.4 c m / s e c . (15 s e c o n d s ) , and f i n a l l y 32.1 c m / s e c . f o r t h e d e s i r e d swimming p e r i o d o f 1, 5, 15, 30, 60 m i n u t e s o r 4 - 8 h o u r s ( l o n g t e r m ) . To a v o i d s t r e s s , t h e g r i d a t t h e r e a r o f t h e w a t e r t u n n e l was n o t e l e c t r i f i e d ; i n a c t i v e f i s h w ere g e n t l y t a p p e d on t h e t a i l w i t h an a l u m i n u m r o d t o i n d u c e swimming. C h r o n i c non-swimmers we r e d i s c a r d e d . A t t h e e n d o f t h e e x p e r i m e n t a l p e r i o d , t h e t r o u t was r e m o v e d f r o m t h e r e s p i r o m e t e r and w e i g h e d as b e f o r e . C o n t r o l f i s h w ere n e t t e d f r o m t h e i r a q u a r i a a n d h e l d i n t h e a i r f o r 5 s e c o n d s as f o r t h e e x p e r i m e n t a l s . However, t h e y v?ere t h e n r e t u r n e d t o t h e i r i n d i v i d u a l t a n k s and l e f t u n d i s t u r b e d u n t i l t h e a p p r o p r i a t e s a m p l e t i m e ( 1 , 5, 15, 30, 60 m i n u t e s o r 4 - 8 h o u r s ) , when t h e y w e r e r e m o v e d and w e i g h e d a s b e f o r e . A f t e r an e x p e r i m e n t , an a n i m a l was r e t u r n e d t o t h e g e n e r a l h o l d i n g t a n k f o r a t l e a s t 24 h o u r s b e f o r e t h e n e x t t r i a l . D u r i n g t h e c o u r s e o f t h e s t u d y , a few f i s h became n o t i c e a b l y d e - s c a l e d and were s a c r i f i c e d ; r e s u l t s f r o m t h e s e t r o u t were r e j e c t e d . W e i g h t c h a n g e s were e x p r e s s e d as g/100 g o r i g i n a l w e i g h t . 159 RESULTS AND DISCUSSION I I I B e f o r e p r e s e n t a t i o n and d i s c u s s i o n o f t h e r e s u l t s , s e v e r a l p o i n t s o f d a t a i n t e r p r e t a t i o n must f i r s t b e c l a r i f i e d . A m a j o r p o r t i o n o f t h i s s e c t i o n h a s b e e n d e v o t e d t o c o n s i d e r -a t i o n o f t h e r e l a t i o n s h i p b e t w e e n b r a n c h i a l p e r m e a b i l i t y t o o x y g e n and p e r m e a b i l i t y t o w a t e r . As c o n c e n t r a t i o n g r a d i e n t s f o r o x y g e n ( S t e v e n s and R a n d a l l , 1 9 6 7 b) a n d w a t e r b e t w e e n i n t e r n a l a n d e x t e r n a l m i l i e u x w i l l r e m a i n e s s e n t i a l l y i n v a r i a n t u n d e r d i f f e r e n t e x e r c i s e c o n d i t i o n s , i t h a s a g a i n b e e n assumed t h a t t h e m e a s u r e d f l u x e s o f b o t h s u b s t a n c e s a r e r e p r e s e n t a t i v e o f p e r m e a b i l i t i e s . However o x y g e n t r a n s f e r a c r o s s t h e r e s p -i r a t o r y e p i t h e l i u m o c c u r s b y s i m p l e d i f f u s i o n ( R a n d a l l , 1 9 7 0 a ) ; t h e same i s n o t n e c e s s a r i l y t r u e o f w a t e r movement, t h e n a t u r e o f w h i c h i s d e p e n d e n t on t h e p r o p e r t i e s o f t h e membranes t h r o u g h w h i c h t r a n s f e r o c c u r s . U n d e r an o s m o t i c g r a d i e n t , w a t e r f l u x t h r o u g h a p o r o u s membrane p r o c e e d s by b o t h q u a s i -l a m i n a r f l o w ( d e s c r i b e d b y t h e P o i s e u i l l e e q u a t i o n ) a n d s i m p l e d i f f u s i o n a l f l o w ( D a v s o n , 1 9 6 4 ) . As p o r e s i z e i n c r e a s e s , d i f f u s i o n a l t r a n s p o r t becomes i n c r e a s i n g l y l e s s i m p o r t a n t . The b u l k f l o w o f w a t e r t h r o u g h s u c h p o r e s ( D a v s o n , 1 9 6 4 ; E v a n s , 1 9 6 9 b ) a n d t h e i n f l u e n c e o f an u n s t i r r e d l a y e r b o u n d i n g t h e membrane i n q u e s t i o n ( D a i n t y and H o u se,1966) h a v e b e e n p o s t u -l a t e d t o a c c o u n t f o r d i s c r e p a n c i e s i n many b i o l o g i c a l s y s t e m s b e t w e e n d i r e c t l y m e a s u r e d n e t w a t e r t r a n s f e r ( o s m o t i c perme-a b i l i t y ) a n d t h a t c a l c u l a t e d f r o m t h e g r o s s f l u x o f l a b e l l e d w a t e r ( d i f f u s i o n a l p e r m e a b i l i t y ^ A t p r e s e n t , i t i s n o t c l e a r w h e t h e r i n t e l e o s t s , t h e o s m o t i c p e r m e a b i l i t y ( P o s ) , as 160 m e a s u r e d b y u r i n e p r o d u c t i o n i n f r e s h w a t e r o r d r i n k i n g r a t e i n s e a w a t e r , i s r e p r e s e n t a t i v e o f s i m p l e d i f f u s i o n a l p e rme-a b i l i t y ( E d ) o r a more c o m p l e x phenomenon a f f e c t e d b y f l o w t h r o u g h p o r e s o r u n s t i r r e d l a y e r s . I n t h e i n t e r t i d a l f i s h X i p h i s t e r a t r o p u r p u r e u s ( E v a n s , 1 9 6 7 ) a n d P h o l i s g u n n e l i s ( E vans,1969a ) Pos a n d Pd w e r e i n f a i r a g r e e m e n t , b u t f r o m a s u r v e y o f a w i d e r a n g e o f b o t h f r e s h w a t e r and m a r i n e s p e c i e s , E v a n s (1969b) h a s c o n c l u d e d t h a t i t i s n o t y e t p o s s i b l e t o make any d e f i n i t e s t a t e m e n t s a b o u t P o s - P d r e l a t i o n s h i p s , a n d t h u s a b o u t t h e membrane s t r u c t u r e o f t h e p e r m e a b l e s u r f a c e s o f t e l e o s t s . C o n s e q u e n t l y t h e p r e s e n t s t u d y , i n c o m p a r i n g s i m -u l t a n e o u s o x y g e n c o n s u m p t i o n s and u r i n e p r o d u c t i o n s may o r may n o t be r e l a t i n g two s i m p l e d i f f u s i o n a l p e r m e a b i l i t i e s . The f a c t r e m a i n s , h o w e v e r , t h a t t h e data, must r e p r e s e n t e f f e c t i v e b r a n c h i a l p e r m e a b i l i t i e s t o t h e two s u b s t a n c e s , w h i c h a r e t h e p a r a m e t e r s o f i m p o r t a n c e t o t h e a n i m a l i t s e l f i n any a l t e r a t i o n o f t h e r e s p i r a t o r y / o s m o r e g u l a t o r y a d j u s t m e n t a t t h e g i l l s . I t i s p o s s i b l e t h a t t h e s o d i u m r e a b s o r p t i v e m e c h a n i s m ( H i r a n o , p e r s o n a l c o m m u n i c a t i o n t o D . J . R a n d a l l ) o b s e r v e d i n t h e i s o l a t e d t r o u t b l a d d e r w a l l may s e r v e t o a l t e r t h e comp-o s i t i o n o r r e d u c e t h e v o l u m e o f t h e f l u i d f i n a l l y r e l e a s e d t h r o u g h t h e u r o g e n i t a l p a p i l l a i n v i v o . S u c h f u n c t i o n s w o u l d b e l a r g e l y n e g a t e d b y t h e p r e s e n c e o f t h e c a n n u l a p t h u s i n t r o d u c i n g ' some i n a c c u r a c y i n t h e r e s u l t s w i t h r e s p e c t t o t h e n o r m a l c o n d i t i o n . A l l p r e v i o u s d a t a on u r i n e f l o w and comp-o s i t i o n i n t r o u t h a v e b e e n o b t a i n e d t h r o u g h s i m i l a r t e c h n i q u e s o f b l a d d e r i n t e r v e n t i o n (Fromm,1963; Holmes and S t a i n e r , 1 9 6 6 ; E n omoto,1967; Hammond,1969; Hunn e t a l . , 1 9 6 8 ; Hunn,1969; Hunn and W i l l f o r d , 1 9 7 0 ) , s o t h e r e e x i s t s no c o m p a r a t i v e i n f o r m a t i o n 161 o n t h i s p o i n t . U n t i l m e t h o d s a r e d e v e l o p e d f o r t h e c o l l e c t i o n o f u r i n e a f t e r i t l e a v e s t h e a n i m a l , t h e n o r m a l i n v i v o a c t i v i t y o f t h e b l a d d e r w i l l r e m a i n unknown. I t seems l i k e l y , h o w e v e r , t h a t r e a b s o r p t i o n o f w a t e r and i o n s b y t h i s o r g a n , i f i n d e e d o c c u r r i n g a t a l l , w o u l d be m i n i m a l due t o i t s p o o r v a s c u l a r i z -a t i o n and h i g h v o l u m e t o s u r f a c e a r e a r a t i o . C o n s e q u e n t l y e r r o r s i n t r o d u c e d b y d i r e c t c o l l e c t i o n f r o m t h e b l a d d e r a r e p r o b a b l y s m a l l a n d r e l a t i v e l y s y s t e m a t i c i n n a t u r e ; f o r t h e p u r p o s e s o f t h i s s t u d y , t h e y h a v e b e e n d i s r e g a r d e d . A m a r k e d d i u r e s i s s u b s e q u e n t t o u r i n a r y c a t h e t e r i z -a t i o n a n d h a n d l i n g h a s b e e n r e p e a t e d l y d e m o n s t r a t e d i n f r e s h w a t e r s a l m o n i d s (R.M.Holmes,1961; Hammond,1969; Hunn and W i l l f o r d , 1 9 7 0 ) . E v a n s (1969 b) h a s c o r r e l a t e d t h i s phenomenon w i t h an i m m e d i a t e i n c r e a s e i n w a t e r p e r m e a b i l i t y , p r e s u m a b l y b r a n c h i a l , a f t e r s t r e s s . H i c k m a n an d Trump (1969) h a v e s u g g e s t -e d t h a t t h i s a ugmented p e r m e a b i l i t y i s a s s o c i a t e d w i t h an e l e v a t i o n o f o x y g e n u p t a k e d u r i n g t h e p o s t - o p e r a t i v e p e r i o d . M e a s u r e m e n t s o f u r i n e f l o w ( F i g . 24) a n d r e s p i r a t o r y f u n c t i o n s ( F i g . 25) a f t e r MS 222 a n a e s t h e s i a a n d c a n n u l a t i o n i n t h e p r e s e n t s t u d y s u p p o r t e d t h e h y p o t h e s i s o f H i c k m a n and Trump ( 1 9 6 9 ) . " L a b o r a t o r y d i u r e s i s " t h e r e f o r e seems t o r e s u l t f r o m a d i s t u r b a n c e o f t h e r e s p i r a t o r y / o s m o r e g u l a t o r y a d j u s t m e n t i n t h e g i l l s . O x y g en u p t a k e and v e n t i l a t i o n r a t e h a d d e c l i n e d t o a c o n s t a n t l e v e l b y a b o u t 45 h o u r s a f t e r o p e r a t i o n ( F i g . 25) c o r r e s p o n d i n g t o a s i m i l a r s t a b i l i z a t i o n o f u r i n e p r o d u c t i o n ( F i g . 2 4 ) . D e t e r m i n a t i o n s o f u r i n e f l o w and m e t a b o l i c r a t e f o r r e s t i n g s t a t e v a l u e s ( T a b l e X V I ) were p e r f o r m e d on t h e f i f t h p o s t - o p e r a t i v e d a y . The mean o x y g e n c o n s u m p t i o n was e x t r e m e l y 162 F i g u r e 24 The d e c l i n e i n u r i n e f l o w w i t h time a f t e r MS 222 a n a e s t h e s i a and c a t h e t e r i z a t i o n i n 5 t r o u t . Each p o i n t r e p r e s e n t s the flow c a l c u l a t e d from a 24 hour sample p l o t t e d a t the m i d p o i n t o f the c o l l e c t i o n i n t e r v a l . D i f f e r e n t symbols have been used f o r v a l u e s from d i f f e r e n t a n i m a l s . One 72 - 96 hour sample was l o s t . o o o< < o< X z o / / I I / •4 O / J B O / ZD z z oo < u < LU CN I O NO _ J L _ O _ L _ o CN ( J i | / 6>I/|LU ) M O T d 3NlcJPl 163 F i g u r e 25. T h e d e c l i n e i n v e n t i l a t i o n r a t e ( u p p e r f i g u r e ) a n d o x y g e n c o n s u m p t i o n ( l o w e r f i g u r e ) w i t h t i m e a f t e r MS 222 a n a e s t h e s i a a n d c a t h e t e r i z a t i o n i n 3 t r o u t . T h e 5 p o i n t s r e p r e s e n t e d b y b l a c k t r i a n g l e s a t 96 - 120 h o u r s i n e a c h f i g u r e a r e t h e r e s t i n g r a t e s o f T a b l e X V I . r 164 T a b l e XV. P h y s i c a l d i m e n s i o n s o f t h e t r o u t u s e d i n S e c t i o n I I I . Means ~ 1 s t a n d a r d e r r o r . N = 8 Body w e i g h t ( g ) 144.50 t 11.82 L e n g t h (cm) 24.80 - 0.54 F o r k l e n g t h (cm) 23.80 - 0.53 Maximum d e p t h (cm) 4.93 - 0.10 C o e f f i c i e n t o f 1.056"- 0.036 c o n d i t i o n w e i g h t x IOO3 ( f o r k l e n g t h ) T a b l e X V I . R e s t i n g s t a t e v a l u e s o f u r i n e f l o w , o x y g e n u p t a k e , a n d v e n t i l a t i o n r a t e f o r 5 t r o u t i n m e t a b o l i s m b o x e s . D e t e r -m i n a t i o n s w e r e made on t h e f i f t h d a y a f t e r c a n n u l a t i o n . * * F i s h W e i g h t V e n t i l a t i o n r a t e O x y gen c o n s u m p t i o n U r i n e f l o w ( o p e r c . c l o s u r e s / m i n . ) ( m l / k g / h o u r ) ( m l / k g / h r ) #55 166.7 52.9 34.95 2.76 #59 152.0 55.8 23.47 3.26 #63 120.1 58.6 46.39 2.48 #64 105.7 53.1 32.41 3.15 #65 138.9 63.6 69.57 2.78 Mean - 1 56.8 ± 1.99 41.36 - 7.94 2.89 "- 0.14 s t a n d a r d e r r o r * mean o f a t l e a s t 5 d e t e r m i n a t i o n s o v e r 5 h o u r s f o r e a c h f i s h X o v e r 5 h o u r s x 165 s i m i l a r t o t h e s t a n d a r d m e t a b o l i c r a t e m e a s u r e d f o r Salmo  g a i r d n e r i o f t h i s w e i g h t b y Rao (1968) a t 5 ° C . F u r t h e r m o r e t h e u r i n e f l o w means were l o w e r t h a n t h o s e r e p o r t e d f o r r e s t i n g s t a t e t r o u t o f s i m i l a r s i z e (Fromm,1963; Holmes and S t a i n e r , 1 9 6 6 ) a n d c o m p a r a b l e t o t h o s e d e t e r m i n e d i n much l a r g e r s a l m o n i d s (Hammond,1969; H u n n , 1 9 6 9 ) . T h u s t h e v a l u e s p r e s e n -t e d i n T a b l e X V I may be c o n s i d e r e d b a s a l t o s t a n d a r d ..rates ( c f . B r e t t , 1 9 6 2 ) . T h e s e d a t a w i l l b e g i v e n f u r t h e r c o n s i d e r -a t i o n when o b s e r v a t i o n s r e l a t i n g u r i n e p r o d u c t i o n t o o x y g e n u p t a k e a r e p r e s e n t e d . F o u r a n i m a l s (#55, #59, #63, a n d #65) were s u b j e c t e d t o a s t a n d a r d i z e d e x e r c i s e r e g i m e i n t h e swimming r e s p i r o m e t e r as d e s c r i b e d p r e v i o u s l y . L e n g t h y i n t e r r u p t i o n s i n t h e r e g i m e o f f i s h #59 may h a v e c a u s e d a l t e r a t i o n s i n u r i n e f l o w r a t e b u t h a d no o b v i o u s e f f e c t on t h i s t r o u t ' s v e n t i l a t o r y a n d m e t a b o l i c r e s p o n s e s t o e x e r c i s e . The c h a n g e s i n r e s p i r a t i o n r a t e s , t a i l b e a t f r e q u e n c y , a n d o x y g e n u p t a k e a s s o c i a t e d w i t h d i f f e r e n t s e c t i o n s o f t h e p r o t o c o l a r e t a b u l a t e d i n T a b l e X V I I . S e v e r a l p o i n t s a r e w o r t h y o f n o t e . F i r s t l y , d e s p i t e t h e f a c t t h a t t h e f i s h h a d a l r e a d y s p e n t a b o u t 12 h o u r s i n t h e chamber when t h e e x p e r i m e n t commenced, t h e i r i n i t i a l " r e s t i n g " o x y g e n u p t a k e was 3 t i m e s g r e a t e r t h a n t h a t d e t e r -m i n e d i n t h e same a n i m a l s a f t e r 5 d a y s i n t h e m e t a b o l i s m b o x e s ( T a b l e XVI)'. S i m i l a r l y h i g h o x y g e n u p t a k e s a t sub-swimming s p e e d s i n a w a t e r t u n n e l h a v e b e e n o b s e r v e d i n s a l m o n ( B r e t t , 1964) and a r e a s s o c i a t e d w i t h " r e s t l e s s n e s s " ( s p o n t a n e o u s a c t i v i t y ) . S u c h e f f e c t s a r e e x t r e m e l y d i f f i c u l t t o e l i m i n a t e b u t t e n d t o d i s a p p e a r w i t h e x e r c i s e . C o n s e q u e n t l y a v e r a g e m e t a b o l i c r a t e i n c r e a s e d o n l y s l i g h t l y a t t h e l o w e s t swimming T a b l e X V I I . T a i l b e a t f r e q u e n c i e s ( T . B . F . ) , v e n t i l a t i o n r a t e s , a n d o x y g e n c o n s u m p t i o n s d u r i n g e a c h h o u r o f t h e i m p o s e d swimming r e g i m e . Means ± 1 s t a n d a r d e r r o r f o r 4 f i s h . V e l o c i t y 10.7 10.7 10.7 21.4 21.4 21.4 10.7 10.7 10.7 ( c m / s e c ) T . B . F . - - - 77.8 78.3 58.0 -( t a i l b e a t s / m i n ) ± 1 2 . 7 ± 1 3 . 1 ± 1 6 . 0 N = 12 V e n t i l a t i o n r a t e ,.63.0 ^63.5 61.6 ,79.0 75.3 71.6 62.8 63.2 62.2 ( c l o s u r e s / m i n ) ± 2.4: ± 2.7 ± 3.0 ± 3.2 ± 3.0 ± 3.5 ± 2.0 ± 2.4 ± 2.3. N = 12 O x y g e n Consump- . -,128.35 116.14 ,101.55 t i o n ( m l / k g / h r ) ± 24.74 ± 22.67 - 19.21 150.62 119.20 109.74 98.28 112.97 90.97 ± 26.27 ± 13.78 ± 9.14 ± 9.30 ± 7.41 ± 12.35 N C o n t i n u a t i o n o f r e g i m e : V e l o c i t y 32.1 32.1 32.1 10.7 10.7 10.7 42.8 42.8 42.8 ( c m / s e c ) T . B . F . 124.6 124.2 124.3 - 144.6 133.0 137.8 ( t a i l b e a t s / m i n ) ± 4.1 ± 2.0 ± 3.7. , ± 4.5 * 4.4 ± 3.5 N = 12 V e n t i l a t i o n r a t e 89.8 86.7 92.0 66..8 64.1 60.8 102.2 96.7 84.0 ( c l o s u r e s / m i n ) ± 1.8 ± 2 . 4 ± 3.2 ± 1.1 ± 1.4 ± 1.8 ± 2.7 ± 8.2 ± 8.9 N = 12 O x y g e n consump- 222.06 232.24 248.38 139.63 113.72 98.14 299.81 272.35 296.56 t i o n ( m l / k g / h r ) ± 14.29 ± 27.29 ± 19.69 ± 19.81 ± 12.60 ± 9.17 ± 6.05 ± 9.11 ± 5.03 N = 4 T a b l e X V I I . ( C o n t i n u e d ) C o n t i n u a t i o n o f r e g i m e : V e l o c i t y 10.7 10.7 10.7 ( c m / s e c ) T . B . F . - -( t a i l b e a t s / m i n ) N = 12 V e n t i l a t i o n r a t e 66.6 61.4 61.5 ( c l o s u r e s / m i n ) ± 1.5 ± 1.4 ± 2.1 N = 12 O x y g e n consump- 92.61 81.50 94.46 t i o n ( m l / k g / h r ) ± 6.93 ± 12.97 ± 1 4 * 7 0 N - 4 s p e e d ( 2 1 . 4 c m / s e c o n d ) , p r o b a b l y r e f l e c t i n g a d e c r e a s e i n t h e c o n s u m p t i o n a s s o c i a t e d w i t h r e s t l e s s b e h a v i o u r . The o x y g e n u p t a k e s a t t h e two h i g h e s t v e l o c i t i e s ( 3 2.1 c m / s e c o n d a n d 42.8 c m / s e c o n d a t 7° - 9 ° C . ) were c o m p a r a b l e t o t h o s e o b s e r v e d b y Rao (1968) a t t h e s e s p e e d s f o r r a i n b o w s o f t h e same s i z e b u t a t 1 5 ° C . The m e t a b o l i c r a t e s m e a s u r e d h e r e a t 42.8 c m / s e c o n d were i n f a c t g r e a t e r t h a n t h e maximum c o n s u m p t i o n s a s c e r t a i n e d b y Rao (1968) a t 5 ° C . I t w o u l d t h e r e f o r e a p p e a r t h a t t r o u t i n t h e p r e s e n t s t u d y a p p r o a c h e d a c t i v e m e t a b o l i c r a t e s ( B r e t t , 1962) a t r e l a t i v e l y l o w swimming s p e e d s . T h i s e f f e c t was p r o b a b l y a t t r i b u t a b l e t o t h e d r a g c r e a t e d b y t h e t r a i l i n g u r i n a r y c a t h e t e r w h i c h w o u l d g r e a t l y e l e v a t e t h e c o s t o f m a i n -t a i n i n g a p a r t i c u l a r swimming v e l o c i t y . The p r e c i p i t o u s d r o p i n meb'abolic r a t e t o o r i g i n a l l e v e l s a t t h e e n d o f t h e e x e r c i s e p e r i o d s i n d i c a t e d , h o w e v e r , t h a t l i t t l e , i f any, o x y g e n d e b t was i n c u r r e d . By t h e e n d o f t h e r e g i m e , o x y g e n c o n s u m p t i o n s w e r e a c t u a l l y s l i g h t l y b e l o w i n i t i a l " r e s t i n g " v a l u e s , a g a i n p r o b a b l y due t o a d i m i n u t i o n o f s p o n t a n e o u s a c t i v i t y . T h e a v e r a g e d u r i n e f l o w s and o x y g e n c o n s u m p t i o n s o f t r o u t #55, #63, a n d #65 t h r o u g h o u t t h e e x p e r i m e n t a r e i l l u s -t r a t e d i n F i g . 26. U r i n e p r o d u c t i o n m a r k e d l y i n c r e a s e d d u r i n g p e r i o d s o f e x e r c i s e , t h e a u g m e n t a t i o n b e i n g a p p r o x i m a t e l y p r o p o r t i o n a l t o t h e v e l o c i t y i n c r e m e n t . A b r a n c h i a l s o d i u m d e f i c i t a s s o c i a t e d w i t h a c t i v i t y h a s b e e n d e m o n s t r a t e d i n t h e f i r s t two s e c t i o n s ; a s i m i l a r c o n c l u s i o n may now be e x t e n d e d t o b r a n c h i a l w a t e r b a l a n c e . I n a d d i t i o n , t h e d a t a r e v e a l s t h a t , i n g e n e r a l , a l t e r a t i o n s i n w a t e r f l u x ( u r i n e f l o w ) c o r r -e s p o n d e d w i t h c h a n g e s i n o x y g e n c o n s u m p t i o n . C o n s i d e r a t i o n o f t h e d a t a f o r i n d i v i d u a l a n i m a l s i s p a r t i c u l a r l y c o n v i n c i n g 168 F i g u r e 26 Simultaneous changes i n u r i n e flows and oxygen uptakes d u r i n g t h e c o n t i n u o u s imposed swimming regime o f S e c t i o n I I I . Each bar r e p r e s e n t s the averaged r e s p o n s e s o f t r o u t #55, #63, and #65. C r o s s h a t c h i n g i n d i c a t e s p e r i o d s o f e x e r c i s e . The broken l i n e on the u r i n e f l o w bar f o r the i n i t i a l hour o f the f i r s t e x e r c i s e i n t e r v a l r e p r e s e n t s the mean w i t h o u t i n c l u s i o n o f the e x t r e m e l y d i u r e t i c v a l u e o f f i s h #65. I VELOCITY OXYGEN CONSUMPTION 1 URINE FLOW (cm/sec.) (ml/kg/hour) (ml/kg/hour) 169 o f t h i s p o i n t . F i g . 2 7 p r e s e n t s p l o t s o f o x y g e n c o n s u m p t i o n v e r s u s u r i n e p r o d u c t i o n ( w a t e r f l u x ) f o r e a c h s i m u l t a n e o u s d e t e r m i n a t i o n d u r i n g t h e swimming r e g i m e . F o r e a c h t r o u t t h e r e e x i s t e d a h i g h l y s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n b e t w e e n t h e two p a r a m e t e r s , a l t h o u g h t h e s l o p e s a n d i n t e r c e p t s o f t h e r e g r e s s i o n l i n e v a r i e d b e t w e e n i n d i v i d u a l s . I t may be n o t e d t h a t s t a n d a r d o x y g e n c o n s u m p t i o n a n d u r i n e f l o w v a l u e s t a k e n i n t h e m e t a b o l i s m b o x e s ( T a b l e X V I ) were i n g o o d a g r e e m e n t w i t h t h e l i n e s f i t t e d t o t h e d a t a f r o m t h e swimming e x p e r i m e n t s . T h u s o v e r a r a n g e o f o x y g e n u p t a k e s f r o m s u b - s t a n d a r d t o a l m o s t a c t i v e m e t a b o l i c r a t e s , o x y g e n a n d w a t e r f l u x e s were i n an a p p r o x i m a t e l y l i n e a r p o s i t i v e r e l a t i o n s h i p . The r e s u l t s a r e i n t e r p r e t e d i n t e r m s o f g i l l p e r m e a b i l i t y t o w a t e r b e i n g l a r g e l y d e f i n e d b y t h e p a t t e r n o f b r a n c h i a l b l o o d p e r f u s i o n n e c e s s a r y t o e f f e c t a c e r t a i n o x y g e n u p t a k e . Mackay a n d B e a t t y (1968) h a v e s u g g e s t e d a s i m i l a r e x p l a n a t i o n f o r t h e t e m p e r a t u r e d e p e n -d e n c e o f u r i n e p r o d u c t i o n i n t h e w h i t e s u c k e r , C a t o s t o m u s  c o m m e r s o n i i . T h i s c o r r e s p o n d e n c e b e t w e e n g a s a n d w a t e r n e t movements i s p e r h a p s i n d i c a t i v e t h a t t h e c o n t r i b u t i o n o f n o n -d i f f u s i o n a l f l o w t o t o t a l w a t e r e n t r y a c r o s s t h e g i l l s i s r e l a t i v e l y u n i m p o r t a n t . However, c l o s e i n s p e c t i o n o f t h e d a t a f r o m i n d i v i d u a l f i s h r e v e a l s t h a t more c o m p l e x i n t e r a c t i o n s , a s s o c i a t e d w i t h r e d u c t i o n s o f t h e o s m o t i c p e n a l t y o f e x e r c i s e , may be s u p e r -i m p o s e d on t h e g e n e r a l r e l a t i o n s h i p . S u c h c o m p e n s a t i o n s were o c c a s i o n a l l y s e e n i n d r a s t i c m o d i f i c a t i o n o f u r i n e f l o w w i t h i n a swimming p e r i o d f and i n a more g e n e r a l t r e n d o v e r t h e w h o l e swimming r e g i m e . The f o r m e r s h o r t t e r r a e f f e c t may be d e a l t w i t h f i r s t ; F i g . 28 p r e s e n t s t h r e e o f t h e more p r o n o u n c e d 170 F i g u r e 2 7 T h e r e l a t i o n s h i p b e t w e e n o x y g e n c o n s u m p t i o n a n d u r i n e f l o w , c o n s i d e r e d a m e a s u r e o f w a t e r i n f l u x , i n 3 r a i n b o w s s u b j e c t e d t o a c o n t i n u o u s swimming r e g i m e . E a c h p o i n t , ( e x c e p t x's) r e p r e s e n t s a s i m u l t a n e o u s d e t e r m i n a t i o n o f t h e two f a c t o r s o v e r a 1 h o u r p e r i o d . ® = d a t a f r o m f i r s t 6 h o u r s o f t h e r e g i m e . T h e l a b e l l e d p o i n t (21.45 m l / k g / h r ) r e p r e s e n t s an e x t r e m e l y d i u r e t i c v a l u e n o t e d i n F i g . 28, a n d was n o t i n c l u d e d i n t h e c a l c u l a t i o n o f t h e r e g r e s s i o n l i n e o r c o r r e l a t i o n c o e f f i c i e n t . O = d a t a f r o m m i d d l e 9 h o u r s o f t h e r e g i m e . A = d a t a f r o m f i n a l 6 h o u r s o f t h e r e g i m e . x = v a l u e o b t a i n e d f r o m t h e same t r o u t a t r e s t i n a m e t a b o l i s m box ( T a b l e X V I ) ; n o t i n c l u d e d i n t h e c a l c u l a t i o n o f t h e r e g r e s s i o n l i n e o r c o r r e l a t i o n c o e f f i c i e n t . F i s h #65: w a t e r i n f l u x = 1.12 + 0 . 0 3 1 ( o x y g e n u p t a k e ) r = 0.783, p < .001 F i s h #55: w a t e r i n f l u x = 2.55 + O . O l K o x y g e n u p t a k e ) r = 0.744, p < .001 F i s h #63: w a t e r i n f l u x = 1.72 + 0 . 0 1 9 ( o x y g e n u p t a k e ) r = 0.742, p < .001 URINE FLOW ( m l / k g / h o u r ) 171 F i g u r e 28 T h r e e e x a m p l e s o f t h e phenomenon i n w h i c h e x t r e m e l y h i g h u r i n e f l o w s a t t h e s t a r t o f e x e r c i s e w e r e d r a s t i c a l l y r e d u c e d ( a s i n d i c a t e d b y t h e a r r o w s ) d u r i n g c o n t i n u e d sivimming. T h e s e c h a n g e s w e r e n o t a s s o c i a t e d w i t h v a r i a t i o n s i n o x y g e n c o n s u m p t i o n . — ~ T h i s p a t t e r n o f r e n a l - w a t e r e f f l u x a t t h e oTiset o f " a c t i v i t y i s t h o u g h t t o be t h e t y p i c a l r e s p o n s e o f t r o u t w h i c h a r e n o t a l r e a d y " a d a p t e d " t o swimming. C r o s s h a t c h i n g i n d i c a t e s p e r i o d s o f e x e r c i s e . VELOCITY (cm /sec.) O P b» w O N > L • — po OXYGEN CONSUMPTION (ml/kg/hrj URINE FLOW (ml/kg/hr) o c 172 e x a m p l e s o f t h i s phenomenon. I n s u c h c a s e s , e x t r e m e l y h i g h u r i n e d i s c h a r g e s a t t h e b e g i n n i n g o f an e x e r c i s e i n t e r v a l were d r a m a t i c a l l y r e d u c e d b y t h e e n d o f t h e p e r i o d . T h e c h a n g e s w e r e n o t a s s o c i a t e d w i t h any m a r k e d a l t e r a t i o n s o f m e t a b o l i c r a t e . As w i l l b e shown p r e s e n t l y , t h i s e f f e c t p r o b a b l y o c c u r r e d b e c a u s e b r a n c h i a l w a t e r i n f l u x was i n i t i a l l y v e r y h i g h b u t s u b s e q u e n t l y d e c l i n e d . T h i s c o m p e n s a t i o n a p p e a r s s i m i l a r i n m a g n i t u d e and t i m i n g t o t h a t o b s e r v e d f o r s o d i u m e f f l u x i n S e c t i o n I I ; t h e two e f f e c t s may h a v e b e e n c a u s e d b y a common m e c h a n i s m . T h a t t h i s e x c e p t i o n a l d i u r e s i s was o b s e r v e d o n l y o c c a s i o n a l l y i n t h e p r e s e n t s t u d y may be r e l a t e d t o t h e s p o n -t a n e o u s a c t i v i t y e x h i b i t e d b y t h e a n i m a l s a t t h e " r e s t i n g " v e l o c i t y p r i o r t o swimming. T h i s b e h a v i o u r may h a v e b e e n s u f f i c i e n t t o i n d u c e t h e p o s t u l a t e d l o w e r i n g o f b r a n c h i a l p erme-a b i l i t y b e f o r e t h e i m p o s i t i o n o f t h e e x p e r i m e n t a l e x e r c i s e s i t u a t i o n . A more g e n e r a l t e n d e n c y f o r c u r t a i l m e n t o f w a t e r i n f l u x d u r i n g p r o l o n g e d a c t i v i t y was s u g g e s t e d b y t h e r e s p o n s e o f i n d i v i d u a l f i s h o v e r t h e e n t i r e p r o t o c o l . T h i s e f f e c t i s b e s t i l l u s t r a t e d b y t h e p l o t s o f F i g . 27. F o r e a c h t r o u t , i t c a n be s e e n t h a t t h e p o i n t s t a k e n f r o m t h e f i r s t 6 h o u r s o f t h e swimming r e g i m e g e n e r a l l y l i e a b o v e t h e common r e g r e s s i o n l i n e ; t h o s e f r o m t h e m i d d l e 9 h o u r s s t r a d d l e i t ; w h i l e t h e v a l u e s o f t h e f i n a l 6 h o u r s t e n d t o f a l l b e l o w i t . One may s p e c u l a t e t h a t i f en o u g h d a t a were a v a i l a b l e , i t w o u l d be p o s s i b l e t o f i t t h r e e d i f f e r e n t r e g r e s s i o n l i n e s o f s i m i l a r s l o p e b u t p r o g r e s s i v e l y l o w e r e l e v a t i o n t o t h e v a l u e s r e c o r d e d a t t h e b e g i n n i n g , m i d d l e , a n d e n d o f t h e swimming p r o t o c o l f o r e a c h a n i m a l . T he w a t e r e n t r y p e r u n i t o x y g e n u p t a k e o b v i o u s l y 173 d e c r e a s e d as swimming e x p e r i e n c e i n c r e a s e d . F u r t h e r c o n s i d e r -a t i o n w i l l be d e v o t e d t o t h e p o s s i b l e m e c h a n i s m o f t h i s phenomenon i n t h e G e n e r a l D i s c u s s i o n . T h e w e i g h t c h a n g e e x p e r i m e n t s were p e r f o r m e d t o f u r t h e r e l u c i d a t e t h e t i m e c o u r s e o f w a t e r f l u x c h a n g e s a s s o c i a t e d w i t h e x e r c i s e . Due t o t h e known s e n s i t i v i t y o f b r a n c h i a l p e r m e a b i l i t y t o h a n d l i n g e f f e c t s ( E v a n s , 1 9 6 9 b ) , t h e e x p e r i m e n t a l p r o c e d u r e was d e s i g n e d t o i m p o s e as l i t t l e s t r e s s a s p o s s i b l e on t h e t r o u t . As a f u r t h e r p r e c a u t i o n , t h e w e i g h t a l t e r a t i o n s o f an i d e n t i c a l l y h a n d l e d s e t o f c o n t r o l a n i m a l s was a l s o a s c e r t a i n e d . The r e s u l t s f r o m e x p e r i m e n t a l s (swimming a t 32.1 c m / s e c o n d ) and c o n t r o l s ( r e s t i n g i n s e p a r a t e a q u a r i a ) a r e p r e s e n t e d i n F i g . 29. I n c r e a s e i n w e i g h t c o u l d o n l y be c a u s e d b y t h e g a i n o f w a t e r f r o m t h e e n v i r o n m e n t ; d e c r e a s e i n w e i g h t c o u l d r e p r e s e n t n e t w a t e r e f f l u x , e x c r e t i o n o f e l e c t r o l y t e s , a n d " m e t a b o l i c " l o s s e s . However v e r y g e n e r o u s e s t i m a t e s o f t h e l a t t e r two f a c t o r s amounted t o l e s s t h a n 3% o f t h e mean d e c l i n e o f f i s h swum f o r 60 m i n u t e s . C o n s e q u e n t l y , i t seems l e g i t i m a t e t o i n t e r p r e t a l l w e i g h t s h i f t s i n t e r m s o f w a t e r movements. The n e t w a t e r b a l a n c e o f t h e e x e r c i s e d t r o u t e x h i b i t e d a t r i p h a s i c r e s p o n s e as swimming t i m e i n c r e a s e d . T h e l a r g e d e c r e a s e o b s e r v e d a f t e r 1 m i n u t e was f o l l o w e d b y a r a p i d r i s e t o p o s i t i v e b a l a n c e ; h o w e v e r b e c a u s e o f v a r i a b i l i t y i n t h e 5 and 15 m i n u t e e x p e r i m e n t a l v a l u e s , t h e i n c r e a s e d i d n o t become s i g n i f i c a n t l y g r e a t e r t h a n c o n t r o l w e i g h t s u n t i l 30 m i n u t e s . B e t w e e n 30 a n d 60 m i n u t e s e x e r c i s e , t h e a n i m a l s r e t u r n e d t o a n e g a t i v e s t a t e ; t h e r e o c c u r r e d o n l y a v e r y s l i g h t f u r t h e r d e c r e m e n t o v e r t h e f o l l o w i n g 3 - 7 h o u r s o f a c t i v i t y . F l u c t u a t i o n s i n c o n t r o l v a l u e s were o f much s m a l l e r m a g n i t u d e 174 F i g u r e 29 C h a n g e s i n b o d y w e i g h t o f r a i n b o w t r o u t ( r e l a t i v e t o o r i g i n a l , v a l u e s d e t e r m i n e d a t l e a s t 8 h o u r s p r e v i o u s l y ) i n r e s p o n s e t o v a r i o u s e x e r c i s e d u r a t i o n s a t 32.1 c m / s e c . i n t h e swimming r e s p i r o m e t e r ( e x p e r i -m e n t a l s ) a n d i n r e s p o n s e t o t h e h a n d l i n g n e c e s s a r y f o r t h e d e t e r m i n a t i o n s a l o n e ( c o n t r o l s ) . Means -1 s t a n d a r d e r r o r . S t a t i s t i c a l C o m p a r i s o n s : (Numbers r e f e r t o t h e t i m e s i n m i n u t e s o f t h e r e s p e c t i v e means o n t h e g r a p h . ) C o n t r o l : F = 2.29, p < .05 30 1 15 5 240 60 E x p e r i m e n t a l s : F = 12.54, p < .005 240 1 60 30 15 5 A = s a m p l e t i m e s a t w h i c h c o n t r o l a n d e x p e r i m e n t a l means a r e s i g n i f i c a n t l y d i f f e r e n t ( p < .05) +1.00-T TIME ( minutes) 175 but mimicked the o s c i l l a t i o n s of experimentals u n t i l 30 minutes post-handling. I t seems probable that the e f f e c t s of handling were very s i m i l a r but l e s s severe than those of swimming. A f t e r 30 minutes, c o n t r o l s returned to t h e i r i n i t i a l weight which was maintained through further a c t i v i t y ( 3 - 7 hours). The data must be i n t e r p r e t e d i n terms of d i f f e r e n c e s between net water i n f l u x across the g i l l s and net water e f f l u x through the uro g e n i t a l p a p i l l a . The large magnitude of the v^eight l o s s a f t e r 1 minute i n d i c a t e d that i t was probably caused mainly by a bladder emptying e f f e c t , although an increase i n glomerular f i l t r a t i o n rate r e s u l t i n g from an i n i t i a l "overshoot" i n systemic blood pressure at the onset of exercise may have contributed to the enhanced water e f f l u x . Hammond (1969.) has demonstrated i n the lake t r o u t , S a l v e l i n u s namaycush^ that pressor e f f e c t s can markedly elevate urine formation. The following weight gain and f i n a l weight l o s s must have been produced by i n e q u a l i t i e s of i n f l u x and e f f l u x , but i t i s not c l e a r whether the former, the l a t t e r , or both processes were changing. The urine production data i s informative i n t h i s respect. A f t e r 60 minutes of swimming, the net weight l o s s r e l a t i v e to the gain at 30 minutes was 1.13 g/100 g. Even i f no i n f l u x occurred a f t e r 30 minutes, a highly u n l i k e l y s i t u -a t i o n , the urine production over the f i r s t hour of swimming must have exceeded 11 ml/kg. I t i s probable that the actual r a t e was much higher. Therefore the weight change animals were obviously behaving as the examples of F i g . 28 which underwent a much greater d i u r e s i s during the f i r s t one or two hours of swimming than during subsequent hours. In such cases there was l i t t l e , i f any, augmentation of urine production 176 d u r i n g t h e f i r s t 15 m i n u t e s o f e x e r c i s e . T h e f a c t t h a t t h i s t y p e o f r e s p o n s e d i d n o t commonly o c c u r a t t h e o n s e t o f e x e r -c i s e i n t h e u r i n a r y c a t h e t e r i z e d t r o u t may a g a i n be a t t r i b u t e d t o t h e i r s p o n t a n e o u s a c t i v i t y a n d e x p e r i e n c e i n t h e r e s p i r o m e t e r w h i c h c o u l d h a v e " a d a p t e d " them t o e x e r c i s e p r i o r t o t h e swim-m i n g r u n s . T h e e x p e r i m e n t a l s o f t h e x ^ e i g h t c h a n g e g r o u p h a d , o n t h e o t h e r h a n d , b e e n q u i e t l y r e s t i n g i n d a r k e n e d a q u a r i a p r i o r t o o b l i g a t o r y swimming. T h u s b y i n t e g r a t i n g t h e w e i g h t c h a n g e d a t a ( F i g . 29) w i t h t h e t y p e o f u r i n a r y r e s p o n s e i l l u s t r a t e d i n F i g . 28, t h e f o l l o w i n g e x p l a n a t i o n may be d e v e l o p e d . The n e t w e i g h t i n c r e m e n t a p p e a r i n g b e t w e e n 5 a n d 30 m i n u t e s was c a u s e d b y an e x t r e m e l y h i g h b r a n c h i a l w a t e r i n f l u x w i t h o u t c o m p e n s a t o r y e l e v a t i o n o f r e n a l f u n c t i o n ( e x c e p t f o r t h e i n i t i a l b l a d d e r e m p t y i n g e f f e c t ) . As swimming p r o g r e s s e d , i n f l u x t e n d e d t o d e c r e a s e w h i l e e f f l u x e v e n t u a l l y r o s e , t h e r e b y p r o d u c i n g t h e p r o n o u n c e d d i u r e s i s . T h i s phenomenon f i n a l l y o v e r c o m p e n s a t e d f o r t h e o r i g i n a l w a t e r g a i n r e s u l t i n g i n t h e w e i g h t l o s s a t 60 m i n u t e s . As w e i g h t s m e a s u r e d a t 1 a n d 4 - 8 h o u r s a f t e r t h e s t a r t o f swimming w e r e s i m i l a r , a b a l a n c e s i t u a t i o n b e t w e e n b r a n c h i a l e n t r y a n d r e n a l o u t p u t was r e a c h e d s o o n a f t e r 60 m i n u t e s . T h i s new b a l a n c e ? h o v ; e v e r , w a s s e t a t a n e t b o d y w a t e r c o n t e n t l o w e r f a n d a w a t e r t u r n o v e r r a t e h i g h e r t h a n t h o s e o r i g i n a l l y m a i n t a i n e d . A t e n t a t i v e scheme g r a p h i c a l l y d e s -c r i b i n g t h e a b o v e i n t e r p r e t a t i o n o f w a t e r b a l a n c e d u r i n g e x e r c i s e i n an i n i t i a l l y " n a i v e " t r o u t i s p r e s e n t e d i n F i g . 30. T h e m a i n f e a t u r e s o f t h e m o d e l a r e an i n i t i a l h i g h w a t e r i n f l u x , a d e l a y i n r e n a l a d a p t a t i o n , a s u b s e q u e n t o v e r s h o o t o f t h e e f f l u x p a r a m e t e r as i n f l u x f a l l s , a n d an e v e n t u a l e q u i l i b r i u m 177 Figure 30 A tentative model of the temporal changes occurring in water influx and efflux of the rainbow trout during the onset and continuation of exercise. It has been assumed that the animal i s not already "adapted" to swimming. WATER FLUX RATES (RELATIVE UNITS; 178 b e t w e e n i n f l u x a n d e f f l u x r a t e s . I t may be h y p o t h e s i z e d t h a t as t h e a n i m a l r e a c h e s t h i s new b a l a n c e , i t becomes " a d a p t e d " t o e x e r c i s e s o t h a t b r a n c h i a l a n d r e n a l c o m p o n e n t s o f w a t e r movement a r e now l i n k e d i n some manner and c h a n g e s i m u l t a n e o u s l y w i t h f u r t h e r a l t e r a t i o n s o f m e t a b o l i c demand. A f i n a l g r a d u a l d e c l i n e i n t h e c o u p l e d f l u x e s h a s b e e n i n -c o r p o r a t e d i n t o t h e m o d e l t o r e p r e s e n t t h e p r o g r e s s i v e d e c r e a s e i n w a t e r f l u x p e r u n i t o x y g e n u p t a k e d i s c u s s e d p r e v i o u s l y ( F i g . 2 7 ) . T h e t r i p h a s i c w e i g h t f l u c t u a t i o n ( F i g . 29) may be c o r r e l a t e d w i t h a r e c i p r o c a l t r i p h a s i c r e s p o n s e i n h a e m o g l o b i n and p l a s m a p r o t e i n c o n c e n t r a t i o n s a s c e r t a i n e d a t t h e b e g i n n i n g o f e x e r c i s e i n Salmo g a i r d n e r i b y S t e v e n s (1968 a ) . S t e v e n s c o n c l u d e d t h a t s i n c e t h e r a t i o o f h a e m o g l o b i n c o n c e n t r a t i o n t o p l a s m a p r o t e i n c o n c e n t r a t i o n d i d n o t c h a n g e d u r i n g t h e i r i n d i v i d u a l f l u c t u a t i o n s , t h e e f f e c t s w e r e c a u s e d b y d i f f e r -e n t i a l r a t e s o f w a t e r movement i n t o t h e b l o o d a c r o s s t h e g i l l s a n d o u t o f t h e b l o o d i n t o t h e t i s s u e s . On t h e b a s i s o f t h e p r e s e n t work, t h i s e x p l a n a t i o n may be m o d i f i e d t o i n -e q u a l i t i e s o f b r a n c h i a l w a t e r i n f l u x a n d r e n a l e f f l u x r a t e s . T h e d e c l i n e i n b l o o d v o l u m e a n d r i s e i n p l a s m a s o d i u m l e v e l s o v e r one h o u r o f e x e r c i s e r e p o r t e d i n S e c t i o n I c a n a l s o now be e x p l a i n e d b y t h e s i g n i f i c a n t w a t e r l o s s o b s e r v e d b y 60 m i n u t e s ( F i g . 2 9 ) . T h e m a i n t e n a n c e o f a r e d u c e d p l a s m a v o l u m e d u r i n g e x t e n d e d e x e r c i s e t h r o u g h a d e c r e a s e i n w a t e r c o n t e n t o f f e r s s e v e r a l o b v i o u s b e n e f i t s t o t h e t r o u t . On an o s m o r e g u l a t o r y b a s i s , t h e r e s u l t i n g c o n c e n t r a t i o n o f p l a s m a e l e c t r o l y t e s w o u l d t e n d t o c o m p e n s a t e f o r t h e a u g m e n t e d b r a n c h i a l and r e n a l l o s s e s o f i o n s s u f f e r e d d u r i n g swimming 179 and thus help to preserve the constancy of the i n t e r n a l medium Haemoconcentration would elevate the blood oxygen capacity and therefore favourably a l t e r the r e l a t i o n s h i p between t o t a l oxygen transport and cardiac work. In addition t h i s e f f e c t would increase the b u f f e r i n g capacity of the bloodj and there-fore serve to reduce a c i d o s i s associated with greater muscular a c t i v i t y . The accompanying r i s e i n blood v i s c o s i t y would be unfavourable i n i t s e l f , but would probably be o f f s e t by the o v e r a l l decrease i n systemic r e s i s t a n c e to blood flow c a l c u l a -ted to accompany exercise i n trout (Stevens, 1968 a). The volume reduction of the c i r c u l a t o r y compartment during a c t i v i t y could be f a c i l i t a t e d by an ischemia of "white" muscle postu-l a t e d by Stevens (1968 b), and for which some l i m i t e d evidence was presented i n Section I. This t i s s u e i s i n any case l a r g e l y anaerobic; i f i n f a c t i t continued to receive a blood supply during swimming, there would occur a disadvantageous release of l a c t a t e i n t o the c i r c u l a t i o n , which would tend to i n h i b i t oxygen uptake by haemoglobin at the g i l l s . A decrease i n plasma volume during prolonged exercise would therefore seem to play an i n t e g r a l r o l e i n the p h y s i o l o g i c a l adjustment pf the f i s h to the increased metabolic demands of swimming. Cation l e v e l s were measured i n a l l hourly urine sample from the four exercised t r o u t . As noted previously (p. 156) the method of sample c o l l e c t i o n probably dampened concentration change associated with d i f f e r e n t exercise conditions; the data presented i n Table XVIII therefore represents average ion l e v e l f o r each hour estimated from the curves of concentration versus time (e.g. F i g . 31). Because of large magnitude d i f f e r e n c e s between the samples from d i f f e r e n t animals, ranges rather than T a b l e X V I I I . U r i n e c a t i o n l e v e l s and flows d u r i n g each hour o f the imposed swimming regime. Means and ranges f o r 4 f i s h . I V e l o c i t y (cm/sec) 10.7 10.7 10.7 21.4 21.4 21.4 10.7 U r i n e flow fal/kg/hr) 7.04 3.83-10.17 5.45 2.01-8.62 5.43 3.20-8.35 10.49 4.20-20.21 6.26 4.00-8.35 6.75 5.40-10.06 ' 3. 4.33 30-5.33 U r i n e Na* (uEq/ml) 10.0 5.5-19.5 10.8 5.5-18.5 9.3 4.0-13.8 8.5 4.8-11.3 9.5 4.8-15.0 9.5 5.5-14.0 5 9.5 .5-13.0 • U r i n e K + (uEq/ml) 0.95 0.62-1.17 0.95 0.62-1.29 0.89 042-1.40 0.94 0.70^1.44 1.00 0.65-1.31 1.00 0.60-1.32 0. 1.01 58-1.40 U r i n e C a + + (uEq/ml) 0.96 0.30-1.27 0.99 0.30-1.24 1.06 0.30-1.40 l.|18 0.95-1.75 1.37 0.80-2.05 1.39 0.70-1.95 0. 1.33 72-2.03 U r i n e M g + + (uEq/ml) 0.51 0.15-1.01 0.56 0.15-1.30 0.57 0.05-1.26 0.(83 0.50-1.20 1.15 0.30-1.62 1. 36 0.21-2.28 0. 1.31 28-2.47 C o n t i n u a t i o n o f regime: V e l o c i t y 10.7 (cm/sec) 10.7 32.1 32.1 32.1 10.7 10.7 U r i n e flow (ml/kg/hr) 5.32 3.50-9.27 5.27 3.55-10.06 10.89 5.20-24.86 10.84 5.90-23.09 6.48 5.07-7.50 4.48 2.60-6.2 5 2. 4.22 80-6.25 U r i n e N a + (uEq/ml) 9.6 5.8-13.0 9.4 4.5-14.7 9.5 13.8-16.5 8.5 3.0-14.3 8.5 6.5-10.5 9.3 7.5-10.5 7 9.9 .5-11.8 U r i n e K + (uEq/ml) 0.99 0.45-1.36 0.98 0.35-1.44 1.05 0.26-1.74 1.'07 0.42-1.74 1.01 0.60-1.47 0.99 0.68-1.36 0. 1.01 60-1.43 U r i n e C a + + (uEq/ml) 1.20 0.66-1.93 1.15 0.56-2.07 1.15 0.50-2.11 1.15 0.60-»2.07 \ 1.26 0.62-2.17 1.32 0.73-2.32 0. 1-. 31 80-2.40 U r i n e M g + + (uEq/ml) 1.15 0.35-2.34 1.00 0.32-2.10 0.86 0.35-1.70 0.'97 0.25-1.90 1.25 0.20-2.45 1.39 0.38-2.90 0. 1.33 54-2.60 T a b l e X V I I I . ( C o n t i n u e d ) C o n t i n u a t i o n o f r e g i m e : V e l o c i t y 10.7 42.8 42.8 ( c m / s e c ) U r i n e f l o w 3. .48 7. .68 7 .91 ( m l / k g / h r ) 2 .97--4. 50 5. 40--11 .10 5 .50 -11 .50 U r i n e N a + 10. .5 9, ,4 9 .0 (UEq/ml) 9.5--11 .5 8 .6--10 .00 7.5 -11 .2 U r i n e K + 1. .17 1. .11 1 .13 ( u E q / m l ) 1 .00--1. 32 0. 9 7--1. 22 1 .05 - 1 . 15 U r i n e C a + + 1. .38 1. .13 1 .04 ( u E q / m l ) 0 .83--2. 22 0. 66--1. 85 0 .60 - 1 . 56 U r i n e M g + + 1. .14 0. .62 0 .54 ( u E q / m l ) 0 .46--1. 70 0. 25--1. 00 0 .19 - 1 . 00 42.8 10.7 10.7 10 .7 6.84 2.40 2.23 2 .62 5.30-7.70 1.40-3.09 1.20-2.95 2.00 -3.60 8.3 15.3 17.4 7.0-10.0 12.0-18.0 12.7-19.0 1.16 1.17 1.20 0.98-1.38 1.06-1.30 1.05-1.38 -1.09 1.46 1.65 0.55-1.90 0.63-3.11 0.77-3.11 -0.73 1.54 1.66 0.20-1.67 0.33-4.03 0.50-4.03 — s t a n d a r d e r r o r s h a v e b e e n p r e s e n t e d a s e s t i m a t e s o f v a r i a b i l i t y . S u c h d i v e r s i t y o f v a l u e s b e t w e e n i n d i v i d u a l s i s c h a r a c t e r i s t i c o f t e l e o s t u r i n a r y i o n d a t a (Hammond, 1969; Hunn a n d W i l l f o r d , 1970). Sodium, p o t a s s i u m , c a l c i u m , a n d magnesium c o n c e n t r a -t i o n s i n " r e s t i n g " s a m p l e s (10.7 cm / s e c o n d ) f e l l w e l l w i t h i n t h e r a n g e s r e p o r t e d b y o t h e r w o r k e r s f o r t h i s s p e c i e s (Fromm, 1963; Holmes a n d S t a i n e r , 1 9 6 6 ; Hunn,1969; Hunn a n d W i l l f o r d , 19 70). D u r i n g p e r i o d s o f e x e r c i s e t h e r e was a t e n d e n c y f o r t h e c o n c e n t r a t i o n s o f a l l f o u r m i n e r a l s t o f a l l a s u r i n e v o l u m e i n c r e a s e d . T he r e v e r s e o c c u r r e d u p o n t e r m i n a t i o n o f swimming; t h e s e e f f e c t s become more p r o n o u n c e d d u r i n g t h e l a t t e r p a r t o f t h e e x e r c i s e r e g i m e . I n i n d i v i d u a l a n i m a l s , s o d i u m and p o t a s s i u m l e v e l s v a r i e d o n l y m o d e r a t e l y a n d g e n e r a l l y i n r e l a t i o n t o a l t e r a t i o n s i n u r i n e f l o w . C a l c i u m a n d magnesium c o n c e n t r a t i o n s , h o w e v e r , d e m o n s t r a t e d l a r g e s i m u l t a n e o u s f l u c t -u a t i o n s w h i c h d i d n o t a l w a y s c o r r e s p o n d t o v o l u m e c h a n g e s ( F i g . 31). S i m i l a r o s c i l l a t i o n s i n t h e c o n c e n t r a t i o n s o f t h e s e two d i v a l e n t c a t i o n s h a v e b e e n o b s e r v e d i n t h e u r i n e o f t h e l a k e t r o u t f S a l v e l i n u s n a m a y c u s h (Hammond,1969). m t h a t s t u d y , t h e s e v a r i a t i o n s w e r e a s s o c i a t e d w i t h f l u c t u a t i o n s i n t h e t u b u l a r r e a b s o r p t i o n o f t h e i o n s . T he d a t a a r e s u g g e s t i v e o f some c o u p l i n g i n t h e a c t i v e t r a n s p o r t o f c a l c i u m a n d mag-n e s i u m a c r o s s t h e p r o x i m a l t u b u l e ; H i c k m a n a n d Trump (1969) h a v e i n f a c t p r o p o s e d t h a t t h e t r a n s p o r t o f t h e two e l e c t r o -l y t e s t h r o u g h t h e t u b u l a r e p i t h e l i a l c e l l i s e f f e c t e d b y c l o s e l y r e l a t e d , i f n o t i d e n t i c a l , ATP r e q u i r i n g s y s t e m s . However, t h e r e a s o n f o r a p p a r e n t t e m p o r a l f l u c t u a t i o n s i n t h e a c t i v i t y o f t h i s m e c h a n i s m i s n o t c l e a r . 182 F i g u r e 31 C h a n g e s o f c a t i o n c o n c e n t r a t i o n s i n u r i n e f r o m a s i n g l e t r o u t o v e r t h e c o n t i n u o u s swimming r e g i m e o f S e c t i o n I I I . V a r i a t i o n s i n s o d i u m , an d t o a l e s s e r e x t e n t , p o t a s s i u m l e v e l s were a s s o c i a t e d w i t h u r i n e v o l u m e a l t e r a t i o n s u n d e r d i f f e r e n t e x e r c i s e c o n d i t i o n s . C a l c i u m a n d magnesium l e v e l s , h o w e v e r , f l u c t u a t e d i n s y n c h r o n y , b u t i n d e p e n d e n t l y o f u r i n e f l o w s o r e x e r c i s e c o n d i t i o n s . 183 T h e e l e c t r o l y t e c o n c e n t r a t i o n c h a n g e s o b s e r v e d i n t h e p r e s e n t s t u d y i n d i c a t e t h a t t h e d i u r e s i s a s s o c i a t e d w i t h e x e r -c i s e was somewhat d i f f e r e n t f r o m t h a t o c c u r r i n g a f t e r h a n d l i n g ( R . M . H o l m e s , 1 9 6 1 ) , s e v e r e h y p o x i a ( H u n n , 1 9 6 9 ) , o r a n a e s t h e s i a (Hunn and W i l l f o r d , 1 9 7 0 ) . I n a l l t h e s e l a t t e r s i t u a t i o n s , h i g h f l o w r a t e s w e r e a s s o c i a t e d w i t h m a r k e d i n c r e a s e s i n e l e c t r o l y t e c o n c e n t r a t i o n s ; t h e o p p o s i t e o c c u r r e d d u r i n g swimming. D i u r e t i c s t a t e s i n v o l v i n g i n c r e a s e d u r i n e i o n l e v e l s p r o b a b l y r e f l e c t p r o f o u n d d i s t u r b a n c e s i n t u b u l a r m i n e r a l r e a b s o r p t i v e f u n c t i o n s as w e l l as i n g l o m e r u l a r f i l t r a t i o n r a t e . The e x e r c i s e d i u r e s i s , h o w e v e r , a p p e a r s t o r e p r e s e n t m e r e l y an e x a g g -e r a t i o n o f v a r i a t i o n s w h i c h n o r m a l l y c a n be o b s e r v e d i n r e s t i n g f i s h (Hammond,1969; H i c k m a n a n d T r u m p , 1 9 6 9 ) . S u c h a l t e r a t i o n s a r e m e d i a t e d b y c h a n g e s i n f i l t r a t i o n w i t h o n l y m i n i m a l a l t e r -a t i o n s i n t u b u l a r s a l t c o n s e r v a t i o n f u n c t i o n s . The e f f i c i e n c y o f w a t e r r e a b s o r p t i o n , h o w e v e r , t e n d s t o d e c r e a s e a t h i g h g l o m e -r u l a r c l e a r a n c e r a t e s , t h e r e b y c r e a t i n g l o w e r e l e c t r o l y t e c o n c e n -t r a t i o n s a t h i g h u r i n e f l o w s (Hammond,1969). I n c r e a s e d u r i n a r y d i s c h a r g e s d u r i n g swimming t h e r e f o r e seem t o be an e x a m p l e o f s i m p l e " w a t e r " d i u r e s i s (Hunn,1969) u n c o m p l i c a t e d b y p e r t u r b -a t i o n s o f t u b u l a r i o n t r a n s p o r t m e c h a n i s m s . I t i s i n t e r e s t i n g t o n o t e t h a t n o n - s m o l t i n g r a i n b o w s may be c o n s i d e r e d a s demon-s t r a t i n g a s i m i l a r t y p e o f d i u r e s i s r e l a t i v e t o s m o l t i n g i n d i v i -d u a l s ( Holmes a n d S t a i n e r , 1 9 6 6 ) . S m o l t i n g f i s h , l i k e r e s t i n g f i s h , a r e t h o u g h t t o h a v e a l o w e r u r i n e p r o d u c t i o n b e c a u s e o f a r e d u c e d b r a n c h i a l w a t e r p e r m e a b i l i t y . As p r e v i o u s l y n o t e d ( T a b l e X I ) t h e r e o c c u r r e d an i n c r e a s e d n e t u r i n a r y e f f l u x o f s o d i u m d u r i n g swimming.The m a g n i t u d e o f t h e r e n a l l o s s , h o w e v e r (2.0 - 4.0 ug/100 g / m i n u t e ) 184 was s m a l l r e l a t i v e t o e i t h e r t h e s i m u l t a n e o u s u n i d i r e c t i o n a l ( 2 8 . 5 0 u g / 1 0 0 g / m i n u t e ) o r n e t e f f l u x ( 1 2 .14 ug/100 g / m i n u t e ) a c r o s s t h e b r a n c h i a l e p i t h e l i u m ( T a b l e I I I ) . The e l e v a t e d r e n a l l o s s was i n f a c t common t o a l l f o u r c a t i o n s m e a s u r e d ; t h e a v e r a g e d r e s p o n s e s o f a n i m a l s #55, #63, #65 h a v e b e e n s u m m a r i z e d i n F i g . 32. I n a d i u r e s i s o f t h i s n a t u r e , u r i n a r y s a l t e x c r e t i o n s h o u l d be d e p e n d e n t l a r g e l y on u r i n e v o l u m e as p e r c e n t a g e t u b u l a r r e a b s o r p t i o n o f i o n s w i l l r e m a i n r e l a t i v e l y s t a b l e (Hammond,1969). C o m p a r i s o n o f F i g . 32 w i t h F i g . 26 i n d i c a t e s t h a t , a t l e a s t f o r s o d i u m an d p o t a s s i u m , t h i s r e l a t i o n s h i p was c o n f i r m e d i n t h e p r e s e n t d a t a . I n c r e a s e s i n c a l c i u m and magnesium e x c r e t i o n , w i t h e x e r c i s e w e r e l e s s p r o -n o u n c e d due t o t h e v a r i a t i o n s t h a t were i n d e p e n d e n t o f e x e r c i s e w h i c h a p p a r e n t l y o c c u r r e d i n t h e a c t i v i t y o f t h e r e a b s o r p t i v e m e c h a n i s m f o r t h e s e m i n e r a l s . I t may be n o t e d t h a t t h e r e t r a n s p i r e d g r a d u a l d e c l i n e s i n u r i n a r y s o d i u m an d p o t a s s i u m l o s s r a t e s u n d e r " r e s t i n g " c o n d i t i o n s ( 1 0 . 7 c m / s e c o n d ) o v e r t h e d u r a t i o n o f t h e e x p e r i m e n t a l p r o t o c o l ( F i g . 32) w h i c h were e n t i r e l y d e p e n d e n t on t h e c o n c o m i t a n t d e c r e a s e s i n u r i n e f l o w . I t h a s p r e v i o u s l y b e e n a r g u e d t h a t t h e l a t t e r e f f e c t r e s u l t e d f r o m t h e i m p l e m e n t a t i o n o f c o m p e n s a t o r y m e c h a n i s m s d u r i n g e x -t e n d e d e x e r c i s e t o r e d u c e t h e w a t e r p e r m e a b i l i t y o f t h e g i l l s . T h u s r e n a l a d a p t a t i o n t o r e d u c e t h e u r i n a r y c o m p onent o f m i n e r a l d e f i c i t d u r i n g e x e r c i s e may be s i m p l y a s e c o n d a r y c o n s e q u e n c e o f b r a n c h i a l p e r m e a b i l i t y a d j u s t m e n t . 185 F i g u r e 32 T h e n e t r e n a l e x c r e t i o n o f f o u r c a t i o n s d u r i n g t h e c o n t i n u o u s swimming r e g i m e o f S e c t i o n I I I . E a c h b a r r e p r e s e n t s t h e a v e r a g e d r e s p o n s e s o f t r o u t #55, #63, a n d #65. C r o s s h a t c h i n g i n d i c a t e s p e r i o d s o f e x e r c i s e . VELOCITY(crn/sec) URINARY ELECTROLYTE LOSS (yEq/kg/hour) ( yg/ ]00g./min.) 186 SUMMARY I I I 1. P o s t - c a t h e t e r i z a t i o n d i u r e s i s was a s s o c i a t e d w i t h e l e v a t i o n s o f o x y g e n c o n s u m p t i o n an d v e n t i l a t i o n r a t e i n r a i n b o w t r o u t . A l l t h r e e p a r a m e t e r s h a d s t a b i l i z e d b y 45 h o u r s a f t e r o p e r a t i o n . 2. U r i n e f l o w , c o n s i d e r e d a m e a s u r e o f b r a n c h i a l w a t e r e n t r y , m a r k e d l y i n c r e a s e d d u r i n g p e r i o d s o f e x e r c i s e i n a swimming r e s p i r o m e t e r . A l t e r a t i o n s i n w a t e r f l u x g e n e r a l l y c o r r e s -p o n d e d w i t h c h a n g e s i n o x y g e n u p t a k e . 3. I n i n d i v i d u a l t r o u t , o v e r a r a n g e o f o x y g e n c o n s u m p t i o n s f r o m s u b - s t a n d a r d t o n e a r l y a c t i v e m e t a b o l i c r a t e s , o x y g e n an d w a t e r i n f l u x e s e x h i b i t e d a h i g h l y s i g n i f i c a n t p o s i t i v e c o r r e l -a t i o n . T h e r e s u l t s w e r e i n d i c a t i v e o f c o v a r i a t i o n o f t h e w a t e r a n d o x y g e n p e r m e a b i l i t i e s o f t h e b r a n c h i a l e x c h a n g e r . 4. C o m p e n s a t i o n s a p p a r e n t l y o c c u r r e d t o r e d u c e b r a n c h i a l w a t e r p e r m e a b i l i t y d u r i n g e x e r c i s e . I n a few c a s e s , h i g h u r i n e f l o w s a t t h e b e g i n n i n g o f a swimming p e r i o d were g r e a t l y r e d u c e d a f t e r 1 o r 2 h o u r s . W e i g h t c h a n g e e x p e r i m e n t s i n d i c a t e d t h a t t h i s r e s p o n s e was c h a r a c t e r i s t i c o f f i s h w h i c h were n o t ^ a d a p t e d " t o e x e r c i s e , a n d r e s u l t e d f r o m an e x t r e m e l y h i g h b r a n c h i a l w a t e r e n t r y w h i c h s u b s e q u e n t l y d e c l i n e d . I n a l l a n i -m a l s , w a t e r e n t r y p e r u n i t o x y g e n u p t a k e t e n d e d t o d e c r e a s e o v e r t h e d u r a t i o n o f t h e i m p o s e d e x e r c i s e r e g i m e as swimming e x p e r -i e n c e i n c r e a s e d . 5. W e i g h t c h a n g e s were d e t e r m i n e d d u r i n g e x e r c i s e a s m e a s u r e s o f w a t e r b a l a n c e i n t r o u t w h i c h w e r e " n a i v e " t o swimming. A t r i p h a s i c f l u c t u a t i o n i n b o d y w e i g h t was o b s e r v e d as swimming t i m e was p r o l o n g e d ; an i n i t i a l l o s s (1 m i n u t e ) was f o l l o w e d w i t h a n e t g a i n b y 30 m i n u t e s , an d a f i n a l d e c r e m e n t b e l o w r e s t i n g 187 l e v e l b y 60 m i n u t e s . T h e r e o c c u r r e d o n l y a v e r y s l i g h t f u r t h e r r e d u c t i o n o v e r t h e f o l l o w i n g 3 - 7 h o u r s o f e x e r c i s e . 6. I n t e g r a t i o n o f w e i g h t c h a n g e d a t a w i t h u r i n e f l o w i n f o r m -a t i o n p e r m i t t e d c o n s t r u c t i o n o f a t e n t a t i v e m o d e l o f w a t e r r e g u l a t i o n b y t h e p r e v i o u s l y u n e x e r c i s e d t r o u t d u r i n g swimming. The m a i n f e a t u r e s o f t h i s scheme a r e : an i m m e d i a t e b l a d d e r e m p t y i n g a t t h e o n s e t o f a c t i v i t y ( n e t l o s s ) ; an i n i t i a l h i g h b r a n c h i a l w a t e r i n f l u x w i t h o u t a p p r e c i a b l e m o d i f i c a t i o n o f r e n a l o u t p u t ( n e t g a i n ) ; a s u b s e q u e n t d e c l i n e i n i n f l u x r a t e a n d r i s e i n u r i n a r y e f f l u x r a t e w h i c h e v e n t u a l l y o v e r c o m p e n s a t e s f o r t h e w a t e r a c c u m u l a t i o n ( n e t l o s s ) ; a n d an e v e n t u a l e q u i l i b r i u m b e t w e e n w a t e r e n t r y a n d e x i t s e t a t a h i g h e r t u r n o v e r r a t e a n d l o w e r b o d y w a t e r c o n t e n t t h a n d u r i n g r e s t . 7. T h i s n e t w a t e r d e f i c i t c a n a c c o u n t f o r t h e d e c r e a s e i n b l o o d v o l u m e an d i n c r e a s e i n p l a s m a s o d i u m l e v e l s n o t e d d u r i n g e x e r c i s e i n S e c t i o n I . 8. S o d i u m an d p o t a s s i u m l e v e l s i n u r i n e c o l l e c t e d d u r i n g swimming w e r e g e n e r a l l y s t a b l e b u t t e n d e d t o d e c r e a s e a t h i g h u r i n e f l o w s a n d i n c r e a s e a t low f l o w s . However c a l c i u m a n d m a gnesium c o n c e n t r a t i o n s u n d e r w e n t s i m u l t a n e o u s f l u c t u a t i o n s w h i c h d i d n o t a l w a y s c o r r e s p o n d t o u r i n e v o l u m e a l t e r a t i o n s . 9. T h e a u g m e n t e d u r i n e o u t p u t o f e x e r c i s e t h u s a p p e a r e d t o r e p -r e s e n t a s i m p l e " w a t e r " d i u r e s i s r e s u l t i n g f r o m e l e v a t e d b r a n c h i a l p e r m e a b i l i t y , a n d u n c o m p l i c a t e d by d i s t u r b a n c e s i n t u b u l a r e l e c t r o l y t e r e a b s o r p t i v e f u n c t i o n s . 10. T h e u r i n a r y e x c r e t i o n o f a l l f o u r c a t i o n s w h i c h were m e a s u r e d i n c r e a s e d d u r i n g swimming, a l t h o u g h t h i s t r e n d was o n l y w e l l d e f i n e d f o r s o d i u m a n d p o t a s s i u m . R e n a l s o d i u m e f f l u x ( 2 . 0 - 4.0 ug/100 g / m i n u t e ) a s s o c i a t e d w i t h a c t i v i t y was s m a l l c o m p a r e d t o b r a n c h i a l s o d i u m n e t l o s s r a t e ( 1 2.14 ug/100 g / m i n u t e ) . 188 GENERAL DISCUSSION The p r e s e n t s t u d y h a s d e m o n s t r a t e d t h a t i n c r e a s e s i n o x y g e n u p t a k e a c r o s s t h e g i l l s o f t h e f r e s h w a t e r a d a p t e d r a i n b o w t r o u t were a s s o c i a t e d w i t h s i m i l a r e l e v a t i o n s o f s o d i u m a n d w a t e r movements t h r o u g h t h e b r a n c h i a l s u r f a c e i n t h e d i r e c t i o n o f t h e i r a c t i v i t y g r a d i e n t s . D u r i n g e x t e n d e d e x e r c i s e , m e c h a n i s m s w e r e a p p a r e n t l y i n v o k e d t o r e d u c e t h e s e h y d r o m i n e r a l f l u x e s a n d t h u s a l l e v i a t e t h e o s m o t i c p e n a l t y o f swimming. The most i m p o r t a n t i n f e r e n c e s a n d c o n c l u s i o n s f r o m t h e d a t a h a v e b e e n s u m m a r i z e d i n F i g . 33 f o r p r e v i o u s l y u n -e x e r c i s e d a n i m a l s a t r e s t , d u r i n g i n i t i a l a c t i v i t y ( 5 - 1 5 m i n u t e s ) , a n d a f t e r " a d a p t a t i o n " t o e x e r c i s e (3 h o u r s ) . I n t h e s e m o d e l s , i t h a s b e e n assumed t h a t b a c k -t r a n s p o r t o f s o d i u m i s n e g l i g i b l e i n t h e t r o u t g i l l . T h u s a t r e s t , b r a n c h i a l s o d i u m t r a n s f e r c o m p r i s e s a l a r g e e x c h a n g e d i f f u s i o n c omponent and a s m a l l a c t i v e i n f l u x e l e m e n t , b o t h p r e s u m a b l y g e n e r a t e d i n t h e i n t e r l a m e l l a e e p i t h e l i u m s e r v e d b y t h e f i l a m e n t a l b l o o d p a t h w a y s ; a s m a l l s i m p l e d i f f u s i o n a l e f f l u x o c c u r s a c r o s s t h e t h i n w a l l e d r e s p i r a t o r y l a m e l l a e . T h i s a r e a i s a l s o t h e s i t e o f a c o n s t a n t i n f l u x o f w a t e r w h i c h i s e l i m i n a t e d t h r o u g h t h e k i d n e y t o g e t h e r w i t h a s m a l l u r i n a r y i o n l o s s . D u r i n g i n i t i a l swimming, t h e e n h a n c e d c a r d i a c o u t p u t c a u s e s i n c r e a s e d c i r c u l a t o r y p e r f u s i o n o f t h e r e s p i r a t o r y l a m e l l a e and t h u s e l e v a t e s t h e t o t a l g a s e x c h a n g e c a p a c i t y o f t h e g i l l s . T h i s r e d i s t r i b u t i o n o f b l o o d h a s no a p p a r e n t e f f e c t on t h e c a r r i e r m e d i a t e d s o d i u m t r a n s p o r t m e c h a n i s m s 189 F i g u r e 33 M o d e l s s u m m a r i z i n g i n f o r m a t i o n on s o d i u m a n d w a t e r b a l a n c e i n t h e r a i n b o w t r o u t p r e s e n t e d i n t h i s s t u d y . A n i m a l s a r e i l l u s t r a t e d a t r e s t , s h o r t l y a f t e r t h e o n s e t o f a c t i v i t y ( 5 - 1 5 m i n u t e s ) , and a f t e r p r o l o n g e d e x e r c i s e . B l o o d v o l u m e c h a n g e s a r e i n -d i c a t e d b y t h i n a r r o w s a n d f l u x r a t e s b y t h i c k a r r o w s ; t h e s i z e o f t h e l a t t e r r e p r e s e n t s t h e mag-n i t u d e o f t h e f l u x r a t e . I t h a s b e e n assumed t h a t t h e a n i m a l i s n o t a l r e a d y " a d a p t e d " t o swimming. Respiratory Lamellar Pathway Filamental Pathways Blood Volume j White'Muscle RESTING Active Transport =Water Flux •=Sodium Flux Simple Diffusion Exchange Diffusion SWIMMING ( 5-15 minutes) inary Loss SWIMMING (after 3 hours ) 1 9 0 s u p p l i e d b y t h e f i l a m e n t a l p a t h w a y s , b u t m a r k e d l y augments t h e d i f f u s i o n a l l o s s o f t h e i o n a c r o s s t h e l a m e l l a r s u r f a c e , t h e r e b y c r e a t i n g a s o d i u m d e f i c i t . W a t e r e n t r y i s a l s o g r e a t l y e l e v a t e d w i t h o u t a p p r e c i a b l e c h a n g e i n r e n a l o u t p u t . An i n c r e a s e d b l o o d v o l u m e r e s u l t s . A f t e r p r o l o n g e d e x e r c i s e , t h e p a t t e r n o f g i l l b l o o d f l o w p r o b a b l y r e m a i n s s i m i l a r t o t h a t a t t h e s t a r t o f swimming. However c o m p e n s a t o r y r e d u c -t i o n s i n b r a n c h i a l h y d r o m i n e r a l p e r m e a b i l i t y h a v e r e t u r n e d t h e d i f f u s i o n a l o u t w a r d movement o f s o d i u m t o r e s t i n g l e v e l s . A c t i v e t r a n s p o r t a n d e x c h a n g e d i f f u s i o n a r e a g a i n i n v a r i a n t . U r i n e f l o w now e q u a l s t h e r a t e o f w a t e r e n t r y ; an i n c r e a s e d r e n a l s o d i u m e x c r e t i o n a c c o m p a n i e s t h e d i u r e s i s . B e f o r e t h i s s t a t e o f w a t e r e q u i l i b r i u m was a t t a i n e d h o w e v e r , u r i n a r y d i s -c h a r g e h a d e x c e e d e d b r a n c h i a l i n f l u x , t h e r e b y r e d u c i n g t h e b l o o d s p a c e b e l o w r e s t i n g v o l u m e . T h i s e f f e c t was a p p a r e n t l y a c c o m p a n i e d b y an i n c r e a s e i n p l a s m a s o d i u m l e v e l s ( t h r o u g h t h e n e t w a t e r l o s s ) and an i s c h e m i a o f " w h i t e " m u s c l e . I n summary, t h e r e s u l t s i n d i c a t e d t h a t t h e e f f e c t i v e p e r m e a b i l i t y o f t h e b r a n c h i a l e x c h a n g e r was an a c c o m m o d a t i o n b e t w e e n t h e demands o f r e s p i r a t i o n a n d o s m o r e g u l a t i o n , and t h a t b o t h t h e d y n a m i c s o f t h i s c o m p r o m i s e a n d t h e f u n c t i o n i n g o f o t h e r s y s t e m s c o u l d be i n f l u e n c e d b y c o m p e n s a t i o n s n e c e s s a r y t o p r e -s e r v e s o d i u m a n d w a t e r b a l a n c e . T h e d i s c u s s i o n s p r e s e n t e d w i t h t h e i n d i v i d u a l s e c t i o n s o f t h i s t h e s i s h a v e d e a l t l a r g e l y w i t h e v a l u a t i o n o f t h e d a t a o b t a i n e d i n t e r r a s o f t h e s a l t and w a t e r b a l a n c e s i t u a t i o n o f t h e a n i m a l u n d e r d i f f e r e n t e x e r c i s e c o n d i t i o n s , a n d w i t h d e v e l -opment o f t h e c o n c e p t o f a r e s p i r a t o r y / o s m o r e g u l a t o r y c o m p r o m i s e a t t h e g i l l s . T he i n t e n t o f t h i s g e n e r a l d i s c u s s i o n i s t o p r o v i d e a more s p e c u l a t i v e t r e a t m e n t o f c e r t a i n p r o b l e m s r a i s e d b y t h e r e s u l t s . F i r s t l y , t h e s t u d y h a s p r o v i d e d ample e v i d e n c e t h a t e l e v a t i o n s o f o x y g e n u p t a k e hamper w a t e r and i o n r e g u l a t i o n ; i t i s t h e r e f o r e p e r t i n e n t t o a s k w h e t h e r o s m o r e g u l a t o r y n e c e s s i t i e s c o u l d i n t u r n h a v e a s i m i l a r l i m i t i n g e f f e c t o n g a s e x c h a n g e . S e c o n d l y , t h e e n a c t m e n t o f c o m p e n s a t o r y m e c h a n i s m t o r e s t r i c t t h e o s m o t i c d e f i c i t o f a c t i v i t y i m p l i e s b o t h t h e p r e s e n c e o f a s y s t e m f o r d e t e c t i o n o f i n t e r n a l m i s a l i g n m e n t and t h e a c t i v i t y o f a m e d i a t o r t o c h a n g e g i l l p e r m e a b i l i t y ; t h e p o s s i b l e n a t u r e s o f b o t h t h e s e f a c t o r s w i l l be c o n s i d e r e d . F i n a l l y , some s u g g e s t i o n s w i l l be a d v a n c e d on t h e a c t u a l way i n w h i c h b r a n c h i a l p e r m e a b i l i t y c o u l d be m o d i f i e d . I n d i s c u s s i n g t h e i n t e r a c t i o n o f g a s e x c h a n g e on t h e one h a n d , a n d i o n a n d w a t e r e x c h a n g e on t h e o t h e r h a n d , i t i s c o n v e n i e n t t o c o n s i d e r c h a n g e s i n b r a n c h i a l p e r m e a b i l i t y i n t e r m s o f p r i m a r y ( o c c u r r i n g a t t h e g i l l s ) a n d s e c o n d a r y ( o c c u r r i n g as a c o n s e q u e n c e o f b r a n c h i a l phenomena) e f f e c t s on r e s p i r a t i o n and o s m o r e g u l a t i o n . T h u s t h e g r e a t e r e f f l u x o f s o d i u m and i n f l u x o f w a t e r a c r o s s t h e g i l l s d u r i n g e x e r c i s e w ere p r i m a r y p e n a l t i e s o n h y d r o m i n e r a l b a l a n c e , w h i l e t h e i n c r e a s e d u r i n a r y l o s s o f i o n s was a p p a r e n t l y a s e c o n d a r y p r o b l e m r e s u l t i n g f r o m t h e e l e v a t e d p e r m e a b i l i t y o f t h e e x c h a n g e s u r f a c e . The p r e s e n t i n v e s t i g a t i o n h a s u t i l i z e d g a s e x c h a n g e as t h e e s s e n t i a l l y i n d e p e n d e n t v a r i a b l e and i o n a n d w a t e r e x c h a n g e as t h e d e p e n d e n t v a r i a b l e s , and t h u s p r o -v i d e s no e v i d e n c e f o r p a r a l l e l p e n a l t i e s on r e s p i r a t o r y b a l a n c e . Two r e c e n t s t u d i e s h a v e i n d i c a t e d , h o w e v e r , t h a t t h e o b l i g a t i o n s o f o s m o r e g u l a t i o n c a n e x e r t a t l e a s t s e v e r e 192 s e c o n d a r y e f f e c t s on o x y g e n m e t a b o l i s m . Rao (1968) w i t h Salmo g a i r d n e r i , and F a r m e r an d B e a m i s h (1969) w i t h T i l a p i a  n i l o t i c a , p e r f o r m e d a l m o s t i d e n t i a l e x p e r i m e n t s i n w h i c h t h e o x y g e n c o n s u m p t i o n o f a n i m a l s a c c l i m a t e d t o and e x e r c i s e d i n a v a r i e t y o f s a l i n i t i e s w ere m e a s u r e d a t s e v e r a l d i f f e r e n t swimming s p e e d s . B o t h s t u d i e s f o u n d t h a t t h e m e t a b o l i c r a t e a t a l l v e l o c i t i e s was l o w e s t i n an i s o s m o t i c s a l i n i t y . T h r o u g h t h e a s s u m p t i o n t h a t t h e c o s t o f o s m o r e g u l a t i o n e q u a l l e d z e r o i n t h i s medium, t h e p r o p o r t i o n o f t o t a l o x y g e n consump-t i o n d e v o t e d t o h y d r o e l e c t r o l y t e r e g u l a t i o n i n o t h e r s a l i n -i t i e s c o u l d be c a l c u l a t e d . F o r f r e s h w a t e r , t h i s f i g u r e was a p p r o x i m a t e l y 2 0 % a t r e s t , a n d d i d n o t c h a n g e w i t h i n c r e a s i n g swimming s p e e d s . T h u s t h e c o s t o f o s m o r e g u l a t i o n r o s e i n p r o p o r t i o n t o t h e o x y g e n f l u x a c r o s s t h e g i l l s . T h i s g r e a t e r m e t a b o l i c demand o f o s m o r e g u l a t o r y f u n c t i o n s i s an o b v i o u s s e c o n d a r y p e n a l t y on r e s p i r a t i o n c a u s e d by e l e v a t i o n s i n b r a n c h i a l p e r m e a b i l i t y . The p r e s e n t s t u d y p r o v i d e s some i n d i c a t i o n , a t l e a s t f o r t h e r a i n b o w t r o u t , o f t h e c a u s e o f t h i s i n c r e a s e d osmo-r e g u l a t o r y c o s t . B r a n c h i a l s o d i u m i n f l u x d i d n o t c h a n g e d u r i n g e x e r c i s e . As t h e r o l e o f b a c k - t r a n s p o r t i n Salmo  g a i r d n e r i g i l l s i s p r o b a b l y n o t i m p o r t a n t , i t w o u l d a p p e a r t h a t a c t i v e s o d i u m u p t a k e r e m a i n e d c o n s t a n t . I n d e e d , t h e d i v e r s i o n o f a g r e a t e r b l o o d f l o w t h r o u g h t h e r e s p i r a t o r y l a m e l l a e w i t h c o n c o m i t a n t d e c r e a s e d p e r f u s i o n o f t h e c e n t r a l s i n u s f i l a m e n t a l p a t h w a y s s e r v i n g t h e i o n t r a n s p o r t i n g c e l l s w o u l d n o t f a v o u r an a u g m e n t a t i o n o f a c t i v e i n f l u x . Wood an d R a n d a l l (19 71) h a v e i n f a c t d e m o n s t r a t e d i n t h e s o u t h e r n f l o u n d e r , P a r a l i c h t h y s l e t h o s t i g m a , t h a t i n d u c e d a n a e m i a , a t r e a t m e n t t h o u g h t t o p r o d u c e c h a n g e s i n b r a n c h i a l b l o o d d i s t r i b u t i o n s i m i l a r t o t h o s e o c c u r r i n g d u r i n g e x e r c i s e , c a u s e d a d e c r e a s e d r a t e o f c a r r i e r m e d i a t e d s o d i u m t r a n s p o r t a c r o s s t h e g i l l s . T he t r o u t a p p a r e n t l y o v e r c o m e s t h e i n i t i a l b r a n c h i a l s o d i u m d e f i c i t o f e x e r c i s e t h r o u g h a r e d u c t i o n o f p a s s i v e p e r m e a b i l i t y , a m e c h a n i s m w h i c h may w e l l be f a r l e s s e x p e n s i v e y e t a c h i e v e t h e same e f f e c t as an e l e v a t i o n o f a c t i v e i n f l u x . B r a n c h i a l w a t e r e n t r y , however, i n c r e a s e d i n a p p r o x i m a t e l y l i n e a r f a s h i o n w i t h o x y g e n c o n s u m p t i o n , an d was o n l y p a r t i a l l y r e d u c e d b y c o m p e n s a t o r y c h a n g e s . The e x p e n s e o f r e n a l w a t e r e l i m i n a t i o n w o u l d , t h e r e f o r e , seem a more imp-o r t a n t f a c t o r i n t h e i n c r e a s e o f o s m o r e g u l a t o r y c o s t w i t h r i s i n g o x y g e n u p t a k e , f o r b o t h g l o m e r u l a r f i l t r a t i o n r a t e and t h e a c t i v e t u b u l a r r e a b s o r p t i o n o f some e l e c t r o l y t e s p r o b a b l y i n c r e a s e s i n p r o p o r t i o n t o w a t e r i n f l u x . T h e r e e x i s t s no d i r e c t e v i d e n c e t h a t h y d r o m i n e r a l r e g u l a t i o n c a n h a v e a p r i m a r y l i m i t i n g e f f e c t on o x y g e n u p t a k e a t t h e g i l l s . T he e x i s t e n c e , o f s u c h a phenomenon w o u l d mean t h a t t h e o x y g e n c o n s u m p t i o n f o r a g i v e n swimming s p e e d was l e s s t h a n t h a t o p t i m a l t o s u p p o r t t h a t e x e r c i s e c o n d i t i o n b e c a u s e o s m o r e g u l a t o r y c o n s i d e r a t i o n s p r e v e n t e d t h e n e c e s s a r y i n c r e a s e i n e f f e c t i v e g i l l p e r m e a b i l i t y . A somewhat o b l i q u e i n d i c a t i o n t h a t t h e r e i s no p r i m a r y i n h i b i t i o n o f o x y g e n e x c h a n g e i s " p r o v i d e d b y t h e r e p o r t s o f Rao (1968) an d F a r m e r and B e a m i s h (1969) t h a t t h e c o s t o f swimming i s t h e same i n an i s o s m o t i c s o l u t i o n as i n f r e s h w a t e r . However i t must be n o t e d t h a t t h e s e w o r k e r s c a l c u l a t e d t h e o x y g e n c o n s u m p t i o n d e v o t e d t o e x e r c i s e t h r o u g h s u b t r a c t i o n o f t h e c o s t o f osmo-r e g u l a t i o n f r o m t h e d i f f e r e n c e b e t w e e n s t a n d a r d and swimming 194 m e t a b o l i c r a t e s ; t h e c o s t o f o s m o r e g u l a t i o n h a d p r e v i o u s l y b e e n d e r i v e d as s t a t e d a b o v e . One c o u l d o b j e c t t h a t t h e c o s t o f o s m o r e g u l a t i o n was i n f a c t g r e a t e r t h a n t h a t computed / b u t was n o t m a n i f e s t e d b e c a u s e t h e a n i m a l s assumed an o x y g e n d e b t r a t h e r t h a n f u r t h e r i n c r e a s i n g t h e i r g i l l p e r m e a b i l i t y and t h u s c o m p o u n d i n g t h e i r o s m o r e g u l a t o r y d i s e q u i l i b r i a . T h i s c r i t -i c i s m i s l a r g e l y n e g a t e d b y t h e f a c t t h a t Rao (1968) a l l o w e d h i s a n i m a l s t o come i n t o a s t e a d y s t a t e a t a p a r t i c u l a r a c t i v i t y l e v e l . However e x p e r i m e n t s i n w h i c h b o t h t h e o x y g e n u p t a k e d u r i n g t h e swimming an d t h e amount d e v o t e d t o r e p a y m e n t o f any a n a e r o b i c a l l y p r o d u c e d d e b t a f t e r e x e r c i s e a r e c o m p a r e d b e t w e e n f i s h i n f r e s h w a t e r a n d i s o s m o t i c e n v i r o n m e n t s s h o u l d d e m o n s t r a t e more c l e a r l y w h e t h e r o r n o t a p r i m a r y d e p r e s s a n t e f f e c t o f o s m o r e g u l a t i o n on o x y g e n u p t a k e i s b u i l t i n t o t h e p h y s i o l o g y o f t h e t r o u t . T h a t t h i s phenomenon may n o t e x i s t , i . e . t h a t t h e b r a n c h i a l c o m p r o m i s e i s w e i g h t e d i n f a v o u r o f g a s e x c h a n g e , seems r e a s o n a b l e i n a s m u c h as h y d r o m i n e r a l i m b a l a n c e may be a t l e a s t p a r t i a l l y c o r r e c t e d b y p e r m e a b i l i t y and b l o o d v o l u m e c h a n g e s , w h i l e t h e r e a p p a r e n t l y e x i s t s no p a r a l l e l m e c h a n i s m f o r r e d u c i n g t h e m e t a b o l i c c o s t o f a c e r t a i n e x e r c i s e l e v e l . T h e m i s a l i g n m e n t d e t e c t i o n s y s t e m w h i c h must be r e s p o n s i b l e f o r t h e i n i t i a t i o n o f c o m p e n s a t o r y o s m o r e g u l a t o r y e f f e c t s d u r i n g swimming a c t i v i t y may a c t i n one o f two ways. F i r s t l y , a d i r e c t s e n s i n g o f d i s t u r b a n c e s i n t h e h y d r o m i n e r a l c h a r a c t e r i s t i c s o f t h e i n t e r n a l e n v i r o n m e n t may o c c u r . S u c h an a r r a n g e m e n t , w i t h o s m o r e c e p t o r s i n t h e h y p o t h a l a m u s r e s p o n s i v e t o c h a n g e s i n p l a s m a o s m o t i c p r e s s u r e , and v o l u m e r e c e p t o r s i n r e n a l a f f e r e n t a r t e r i o l e s and t h e l e f t a t r i a l w a l l s e n s i t i v e t o b l o o d p r e s s u r e v a r i a t i o n s , h a s b e e n d e s c r i b e d i n mammals (D.M..Woodbury, 1 9 6 5 ) . M o r e o v e r , t h e r e e x i s t s l i m i t e d e v i d e n c e t h a t an a n a l o g o u s , a l t h o u g h q u a l i t a t i v e l y d i f f e r e n t , s y s t e m may e x i s t i n t e l e o s t s . I n f u s i o n o f h y p o t o n i c o r h y p e r -t o n i c s o d i u m c h l o r i d e s o l u t i o n s i n t o t h e g o l d f i s h , C a r a s s i u s  a u r a t u s ^ p r o d u c e d a l t e r a t i o n s o f b r a n c h i a l u n i d i r e c t i o n a l f l u x r a t e s i n d i r e c t i o n s t e n d i n g t o r e s t o r e t h e i o n i c e q u i l i b r i u m o f t h e p l a s m a ; m a n n i t o l i n j e c t i o n s o f t h e same t o n i c i t y d e m o n s t r a t e d t h a t t h e r e s p o n s e s were m e d i a t e d by n e i t h e r c h a n g e s i n e x t r a c e l l u l a r s p a c e ( v o l u m e ) o r o s m o t i c p r e s s u r e , b u t b y t h e d i s t u r b a n c e o f i n t e r n a l e l e c t r o l y t e c o n c e n t r a t i o n s ( B o u r g u e t e t a _ l . , 1 9 6 4 ) . M a y e r and N i b e l l e (1970) h a v e o b -s e r v e d s i m i l a r e f f e c t s i n t h e e e l , A n g u i l l a a n g u i l l a . , The a d m i n i s t r a t i o n o f t h e same d i l u t e and c o n c e n t r a t e d s a l i n e l o a d s p r o d u c e d a d i u r e s i s a n d a a n t i d i u r e s i s r e s p e c t i v e l y i n t h e g o l d f i s h ; t h e o s m o t i c d i u r e s i s r e s u l t i n g f r o m m a n n i t o l i n -j e c t i o n s h o w e v e r p r e v e n t e d e l u c i d a t i o n o f t h e s p e c i f i c s t i m u l i i n v o l v e d i n t h e r e n a l r e s p o n s e s ( B o u r g u e t e t a l . , 1 9 6 4 ) . T h e s e w o r k e r s p o s t u l a t e d t h a t t h e o b s e r v e d o v e r a l l e f f e c t s c o u l d w e l l be c a u s e d b y t h e d i r e c t a c t i o n o f c i r c u l a t o r y i o n l e v e l s on t h e a c t i v i t y o f e n d o c r i n e o r g a n s whose s e c r e t i o n s w ere r e s p o n s i b l e f o r w a t e r and e l e c t r o l y t e economy. T h i s c o n c e p t i s s u p p o r t e d b y t h e work o f Sage (1968) w h i c h r e v e a l e d a g r e a t e r s e c r e t o r y r a t e b y X i p h o p h o r u s s p . p i t u i t a r y p a r a -l a c t i n c e l l s c u l t u r e d on a d i l u t e medium (112 mEq N a + / L ) t h a n on a c o n c e n t r a t e d medium (160 mEq N a + / L ) ; p a r a l a c t i n i s an i m p o r t a n t f a c t o r c o n t r o l l i n g s o d i u m o u t f l u x i n f r e s h w a t e r ( E n s o r and B a l l , 1 9 6 8 ) . However t h e r e c e n t s t u d y o f R i c h a r d s a n d Fromm (1970) on t h e i s o l a t e d p e r f u s e d h e m i b r a n c h s o f Salmo 196 g a i r d n e r i s u g g e s t e d a d i r e c t a c t i o n o f p l a s m a c o n c e n t r a t i o n s on b r a n c h i a l s o d i u m f l u x e s . W h a t e v e r t h e a c t u a l c a u s e s , t h e r e d o e s seem t o e x i s t some d e t e c t i o n o f p l a s m a s a l t l e v e l s i n t r i n s i c t o t h e f u n c t i o n o f c e r t a i n t i s s u e s a n d n o t n e c e s s a r i l y d e p e n d e n t on d i s c r e t e r e c e p t o r s i t e s . T he s e c o n d p o s s i b l e m o n i t o r i n g s y s t e m w o u l d be s e n s i t i v e t o some i n t e r n a l c h a n g e ( s ) a t t e n d a n t t o e x e r c i s e o t h e r t h a n hy d r o e l e c t r o l y t i c d i s a r r a n g e m e n t . The p r e s e n t s t u d y i n d i c a t e s t h a t c h a n g e s i n p l a s m a c o m p o s i t i o n o c c u r r i n g d u r i n g swimming w e r e s l i g h t r e l a t i v e t o t h e e x p e r i m e n t a l d i s t u r b a n c e s i n d u c e d i n t h e a b o v e i n v e s t i g a t i o n s . I n a d d i t i o n , p l a s m a s o d i u m l e v e l s t e n d e d t o r i s e a b o v e r e s t i n g v a l u e s due t o t h e b l o o d v o l u m e r e d u c t i o n , a d e v i a t i o n w h i c h w o u l d e l e v a t e s o d i u m e f f l u x i f t h e m e c h a n i s m s shown b y t h e s e w o r k e r s were i n o p e r a t i o n . T h u s t h e s e c o n d t y p e o f d e t e c t i o n m e c h a n i s m may w e l l be f u n c t i o n a l d u r i n g swimming, t h e e l e c t r o l y t e s e n s i t i v e s y s t e m h a v i n g p e r h a p s b e e n d e s i g n e d f o r t h e more d r a s t i c c h a n g e s w h i c h o c c u r u pon e n t r y i n t o d i f f e r e n t s a l i n i t i e s . I t i s p o s s i b l e t h a t c a t e c h o l a m i n e s , t h e f a c t o r s l a r g e l y r e s p o n s i b l e f o r c a r d i o v a s c u l a r a d a p t a t i o n t o e x e r c i s e , a r e a l s o i n s t r u m e n t a l i n t h e o s m o r e g u l a t o r y a d j u s t m e n t . I n s u c h a scheme, t h e i n c r e a s e d c i r c u l a t o r y l e v e l s o f a d r e n a l i n e a n d n o r a d r e n a l i n e d u r i n g swimming (Nakano an d T o m l i n s o n , 1 9 6 7 ) w o u l d be t h e i n t e r n a l " d i s t u r b a n c e " d e t e c t e d , and w o u l d be r e s -p o n s i b l e f o r . t h e b r a n c h i a l p e r m e a b i l i t y a l t e r a t i o n s . The p l a n o f f e r s an a u t o m a t i c a d a p t a t i o n t o e x e r c i s e w i t h o u t t h e n e c e s s -i t y o f l a r g e p r i o r r e d u c t i o n s o f i n t e r n a l e l e c t r o l y t e l e v e l s . T h e s t i m u l a t o r y e f f e c t o f c a t e c h o l a m i n e s on t h e s e c r e t o r y a c t i v i t y o f t h e a n t e r i o r h y p o p h y s i s i n mammals p r o v i d e s t e n t a t i v e s u p p o r t f o r t h i s h y p o t h e s i s ( R u s s e l , 1 9 6 5 ) ; 1 9 7 p i t u i t a r y h o r m o n e s a r e o f g r e a t i m p o r t a n c e i n t e l e o s t osmo-r e g u l a t i o n . I n r e c e n t y e a r s , i t h a s become c l e a r t h a t o s m o r e g u l -a t i o n i n t e l e o s t s i s an e x c e e d i n g l y i n t r i c a t e f u n c t i o n d e p e n d e n t on an a r r a y o f e n d o c r i n e m e c h a n i s m s . P e r h a p s b e c a u s e o f t h e s e v e r e o s m o t i c s t r e s s i m p o s e d b y t h e a q u e o u s e n v i r o n -ment, w a t e r and i o n r e g u l a t i o n i n f i s h a p p e a r s t o be a much more- c o m p l e x p r o c e s s t h a n i n mammals. T h r e e m a i n e n d o c r i n e s y s t e m s , s e c r e t i o n s o f t h e a n t e r i o r p i t u i t a r y - a d r e n o c o r t i c a l a x i s , a d e n o h y p o p h y s i a l p a r a l a c t i n ( " f i s h p r o l a c t i n " ) , a n d n e u r o h y p o p h y s i a l o c t a p e p t i d e s , a r e now known t o e x e r t c o n t r o l o v e r h y d r o m i n e r a l m e t a b o l i s m . O t h e r a g e n t s , s u c h as t h y r o i d h ormone, g r o w t h hormone, r e n i n , a n d s e c r e t i o n s o f t h e u l t i m o -b r a n c h i a l s and u r o p h y s i s may e m b r o i d e r t h e p a t t e r n l a i d down b y t h e s e d e m o n s t r a t e d i n f l u e n c e s , b u t t h e i r e x a c t r o l e s i n h y d r o e l e c t r o l y t e economy a r e n o t w e l l u n d e r s t o o d a t p r e s e n t . C o n s e q u e n t l y , i t w o u l d be n a i v e t o s u g g e s t t h a t t h e a d j u s t m e n t s w h i c h r e d u c e t h e o s m o r e g u l a t o r y p r o b l e m s o f si^imming i n t r o u t a r e a t t r i b u t a b l e t o a s i n g l e d e f i n i t e s o u r c e . The f o l l -o w i n g d i s c u s s i o n w i l l c o n s i d e r t h e p o s s i b l e r o l e s , i n t h e o b s e r v e d c o m p e n s a t o r y e f f e c t s , o f e a c h o f t h e t h r e e s y s t e m s p r e s e n t l y known t o be o f i m p o r t a n c e i n w a t e r and s a l t b a l a n c e ; t h i s t r e a t m e n t i n no way p r e c l u d e s t h e i n t e r v e n t i o n o f o t h e r h o r m o n e s whose a c t i o n s h a v e n o t y e t b e e n d e f i n e d . A d r e n o c o r t i c o s t e r o i d s , o f w h i c h C o r t i s o l seems t o b e o f m a j o r o s m o r e g u l a t o r y i m p o r t a n c e , a r e r e l e a s e d f r o m t h e i n t e r r e n a l g l a n d , p r o b a b l y u n d e r t h e s t i m u l a t i o n o f a d r e n o -c o r t i c o t r o p i n (A.C.T.H.) f r o m t h e a n t e r i o r l o b e o f t h e p i t u i t a r y ; t h e two e n d o c r i n e o r g a n s a r e t h o u g h t t o be l i n k e d 198 i n a n e g a t i v e f e e d b a c k r e l a t i o n s h i p ( C h e s t e r J o n e s e t a l . , 1 9 6 9 ) . P l a s m a C o r t i s o l l e v e l s i n c r e a s e d u r i n g e x e r c i s e i n Salmo  g a i r d n e r i ( D o n a l d s o n and M c B r i d e , 1 9 6 7 ) , a n d t h u s t h i s hormone w o u l d seem a p r i m e c a n d i d a t e f o r i n v o l v e m e n t i n t h e a d a p t a t i o n t o swimming; however none o f i t s d e m o n s t r a t e d e f f e c t s a r e i n a c c o r d w i t h t h e c o m p e n s a t i o n s ( r e d u c t i o n s i n b r a n c h i a l s o d i u m e f f l u x r a t e a n d w a t e r p e r m e a b i l i t y ) n o t e d i n t h e p r e s e n t i n v e s t -i g a t i o n . E a r l y s t u d i e s on t h e t r o u t i n f a c t i n d i c a t e d t h a t a d r e n a l s t e r o i d s were g e n e r a l l y d e l e t e r i o u s t o o s m o r e g u l a t o r y h o m e o s t a s i s ( H o l m e s , 1 9 5 9 * Holmes a n d B u t l e r , 1 9 6 3 ) , a l t h o u g h t h i s work i s now s u s p e c t b e c a u s e o f t h e u n p h y s i o l o g i c a l l y h i g h d o s e s o f hormones a d m i n i s t e r e d . More r e c e n t i n v e s t i g a t i o n s i n t h e e e l , A n g u i l l a a n g u i l l a / u s i n g s u r g i c a l a d r e n a l e c t o m y a n d C o r t i s o l t h e r a p y , h a v e r e v e a l e d t h a t C o r t i s o l m a i n t a i n s t h e n o r m a l f u n c t i o n o f t h e a c t i v e b r a n c h i a l s o d i u m pump, p r o m o t i n g e f f l u x i n s e a w a t e r and i n f l u x i n f r e s h w a t e r ; h o w e v e r i t h a s no e f f e c t on e f f l u x i n f r e s h w a t e r . F u r t h e r m o r e , A.C.T.H. a n d C o r t i s o l augment b r a n c h i a l w a t e r p e r m e a b i l i t y i n t h e g o l d f i s h , C a r a s s i u s a u r a t u s w i t h o u t a c c o m p a n y i n g d i u r e s i s ( L a h l o u a n d G i o r d a n , 1 9 7 0 ) . T h i s l a t t e r a c t i o n i s r e m i n i s c e n t o f t h e o b s e r v e d w e i g h t g a i n d u r i n g t h e f i r s t few m i n u t e s o f swimming i n t h e t r o u t ( F i g s . 29 a n d 3 0 ) . T h u s , o n p r e s e n t e v i d e n c e , i t w o u l d a p p e a r t h a t t h e a n t e r i o r p i t u i t a r y - i n t e r r e n a l a x i s i s n o t i n v o l v e d i n t h e o s m o r e g u l a t o r y a d j u s t m e n t t o e x e r c i s e , a n d may i n f a c t c o n t r i b u t e t o w a t e r b a l a n c e p r o b l e m s a t t h e o n s e t o f a c t i v i t y . However t h e m o b i l i z a t i o n o f C o r t i s o l d u r i n g swimming i s p e r h a p s o f o v e r r i d i n g i m p o r t a n c e i n c a r b o h y d r a t e m e t a b o l i s m . 199 P a r a l a c t i n , o r i g i n a t i n g f r o m t h e t e l e o s t a d e n o h y p o -p h y s i s , o r mammalian p r o l a c t i n w h i c h m i m i c s i t s a c t i o n , h a v e b e e n shown t o l i m i t t h e p a s s i v e e f f l u x o f s o d i u m , p r e s u m a b l y l a r g e l y a t t h e g i l l s , i n a v a r i e t y o f t e l e o s t s ( e . g . M a e t z e t aJL.,1967 a, b; E n s o r and B a l l , 1968; B a l l , 1 9 6 9 ) . I t i s now e v i d e n t t h a t f i s h p r o l a c t i n i s n o t e s s e n t i a l f o r l i f e i n f r e s h w a t e r i n a l l s p e c i e s , a n d t h a t i t s f u n c t i o n , r a t h e r t h a n as an " a l l o r n o t h i n g s u r v i v a l m e c h a n i s m " , l i e s i n t h e m o d u l a t i o n , t h r o u g h s i m p l e p e r m e a b i l i t y e f f e c t s , o f s o d i u m e f f l u x a c r o s s t h e g i l l s t o m a i n t a i n i o n i c h o m e o s t a s i s ( B a l l , 1 9 6 9 ) . C o n s e q u e n t l y t h i s hormone c o u l d be o f m a j o r i m p o r t -a n c e i n r e d u c i n g t h e a u g m e n t e d b r a n c h i a l s o d i u m l o s s w h i c h a c c o m p a n i e s swimming i n t r o u t . However mammalian p r o l a c t i n ( a n d p r e s u m a b l y p a r a l a c t i n ) , l i k e A.C.T.H. an d C o r t i s o l , t e n d s t o e l e v a t e b r a n c h i a l w a t e r p e r m e a b i l i t y , a t l e a s t i n t h e g o l d -f i s h ( L a h l o u a n d G i o r d a n , 1 9 7 0 ) a n d t h e p l a i n s k i l l i f i s h F u n d u l u s k a n s a e ( P o t t s and F l e m i n g , 1 9 7 0 ) . N e u r o h y p o p h y s i a l o c t o p e p t i d e s a r e p r e s e n t l y o f d i s p u t e d o s m o r e g u l a t o r y f u n c t i o n i n f r e s h w a t e r t e l e o s t s . T h e y may p r o d u c e an e l e v a t i o n o f b r a n c h i a l s o d i u m i n f l u x ( M a e t z a n d J u l i e n , 1 9 6 1 ) o r o f b o t h u n i d i r e c t i o n a l f l u x e s ( e . g . M o t a i s a n d M a e t z , 1964; M a e t z e t a l . , 1964b); a n d e i t h e r a d i u r e s i s ( e . g . M a e t z e_t j a l . , 1964 b ; L a h l o u and G i o r d a n , 1970) o r an a n t i -d i u r e s i s ( H o l m e s , 1 9 6 1 ; Hammond,1969). I t i s p r o b a b l e t h a t much o f t h i s d i s a g r e e m e n t a r i s e s f r o m t h e f a i l u r e o f many i n v e s t i g a t o r s t o a d e q u a t e l y c o n t r o l s t r e s s o r u s e p h y s i o l o g -i c a l d o s e s o f p u r e l y t e l e o s t e a n p r i n c i p l e s ( a r g i n i n e v a s o t o c i n a n d i s o t o c i n ) . N e i t h e r o f t h e r e p o r t e d s a l t b a l a n c e e f f e c t s a r e i n a g r e e m e n t w i t h t h e c o m p e n s a t i o n s o b s e r v e d i n t h e 200 p r e s e n t s t u d y , b u t t h e w h o l e p r o b l e m o f n e u r o h y p o p h y s i a l i n f l u e n c e on b r a n c h i a l s o d i u m movements seems w o r t h y o f f u r t h e r i n v e s t i g a t i o n w i t h more p r u d e n t t e c h n i q u e s . P e r k s (1969) h a s i n f a c t s u g g e s t e d t h a t a r g i n i n e v a s o t o c i n may a c t t o c o n t r o l s o d i u m f l u x e s a c r o s s t h e g i l l s d u r i n g e x e r c i s e . T he most c a r e f u l w a t e r b a l a n c e s t u d y a p p e a r s t o be t h a t o f Hammond (1969) on t h e l a k e t r o u t , S a l v e l i n u s n a m a y c u s h , who d e m o n s t r a t e d a m a r k e d a n t i d i u r e s i s , m e d i a t e d a l m o s t e n t i r e l y b y a r e d u c t i o n i n g l o m e r u l a r f i l t r a t i o n r a t e , f o l l o w i n g i n t r a v a s c u l a r i n f u s i o n o f o n l y nanogram amounts o f a r g i n i n e v a s o t o c i n . U n f o r t u n a t e l y Hammond d i d n o t m e a s u r e b r a n c h i a l w a t e r e n t r y o r w e i g h t v a r i a t i o n s o c o u l d n o t c o n c l u d e w h e t h e r t h e d e c r e a s e d u r i n e f l o w was a d i r e c t r e n a l e f f e c t o f t h e hormone o r a s e c o n d a r y phenomenon r e s u l t i n g f r o m a d e c r e a s e i n b r a n c h i a l w a t e r perm-e a b i l i t y . L a h l o u a n d G i o r d a n ( 1 9 7 0 ) , h o w e v e r , h a v e r e c e n t l y d e m o n s t r a t e d t h a t a t l e a s t p h a r m a c o l o g i c a l d o s e s o f t h e same hormone g r e a t l y d e p r e s s t h e b r a n c h i a l w a t e r e x c h a n g e o f C a r a s s i u s a u r a t u s . T he i m p l i c a t i o n o f n e u r o h y p o p h y s i a l p r i n c i p l e s i n t h e c o r r e c t i o n o f h y d r o m i n e r a l d i s e q u i l i b r i u m d u r i n g e x e r c i s e t h e r e f o r e r e m a i n s q u i t e p o s s i b l e . One may c o n j e c t u r e t h a t a r g i n i n e v a s o t o c i n s e r v e s p r i m a r i l y t o l i m i t w a t e r i n f l u x w h i l e a d e n o h y p o p h y s i a l p r o l a c t i n r e d u c e s p a s s -i v e s o d i u m e f f l u x a c r o s s t h e g i l l s . T h e f o r m e r a g e n t c a n a c t a l m o s t i m m e d i a t e l y ( l e s s t h a n 15 m i n u t e s a f t e r i n j e c t i o n (Hammond,1969)), b u t t h e t i m e c o u r s e o f t h e p a r a l a c t i n i n f l u e n c e i s i l l - d e f i n e d ; h o w e v e r on t h e b a s i s o f t h e work o f E n s o r a n d B a l l ( 1 9 6 8 ) , i t w o u l d seem t o e x e r t p e r m e a b i l i t y e f f e c t s w i t h i n 4 h o u r s . T h e s e l a t e n c i e s do n o t o f f e r s e r i o u s d i s a g r e e m e n t t o t h e t i m e c o u r s e s o f c o m p e n s a t o r y phenomena 201 o b s e r v e d i n t h e p r e s e n t s t u d y . The m e c h a n i s m by w h i c h e n d o c r i n e a g e n t s a c t on t h e g i l l t i s s u e r a i s e s f u n d a m e n t a l q u e s t i o n s a b o u t t h e manner o f hormone a c t i o n on membranes w h i c h a r e b e y o n d t h e s c o p e o f t h i s d i s c u s s i o n . However one may s p e c u l a t e on t h e n a t u r e o f t h e e f f e c t i v e p e r m e a b i l i t y r e d u c t i o n t o s o d i u m and w a t e r d u r i n g e x t e n d e d e x e r c i s e . C h a n g e s w h i c h a r e n o t d e p e n d e n t on a s y n t h e t i c m o d i f i c a t i o n o f c e l l s t r u c t u r e a n d w h i c h a r e e a s i l y r e v e r s i b l e w o u l d seem l e a s t c o s t l y a n d m o s t p r a c t i c a l . T h r e e p o s s i b i l i t i e s may be a d v a n c e d . F i r s t l y , d i v a l e n t c a t i o n s s u c h as c a l c i u m a n d magnesium h a v e l o n g b e e n known t o d e p r e s s c e l l p e r m e a b i l i t y b y r e d u c i n g t h e r e p u l s i o n o f f i x e d a n i o n s i n t h e membrane s t r u c t u r e a n d t h e r e f o r e a l l o w i n g c l o s e r a p p o s i t i o n o f o r g a n i c m o l e c u l e s ( P o t t s a n d F l e m i n g , 1 9 7 0 ) . F u r t h e r m o r e , t h e e x t e r n a l a d m i n i s t r a t i o n o f c a l c i u m i o n s r e d u c e d s o d i u m l o s s i n t h e ammocoete, L a m p e t r a p l a n e r i ( M o r r i s and B u l l , 1 9 6 8 ) a n d b r a n c h i a l w a t e r e x c h a n g e i n t h e p l a i n s k i l l i f i s h , F u n d u l u s  k a n s a e ( P o t t s a n d F l e m i n g , 1 9 7 0 ) . A h o r m o n a l l y s t i m u l a t e d a l t e r a t i o n i n d i v a l e n t c a t i o n m e t a b o l i s m c o u l d be i n v o l v e d i n t h e p e r m e a b i l i t y c h a n g e s d u r i n g swimming. S e c o n d l y , t h e s e c r e t i o n o f mucus by b r a n c h i a l e p i d e r m a l c e l l s may c h a n g e t h e e f f e c t i v e d i f f u s i o n d i s t a n c e and r e s i s t a n c e o f t h e e x c h a n g e s u r f a c e . M o r e o v e r , t h e r e e x i s t s some e v i d e n c e t h a t p a r a l a c t i n s t i m u l a t e s mucus p r o d u c t i o n a t t h e g i l l s ( s e e B a l l , 1 9 6 9 ) ; t h i s a c t i o n may e x p l a i n i t s e f f e c t on p a s s i v e s o d i u m e f f l u x b u t n o t o n b r a n c h i a l w a t e r p e r m e a b i l i t y ( L a h l o u a n d G i o r d a n , : 19 7 0 ) . F i n a l l y an i n v o l v e m e n t o f t h e c y t o p l a s m i c f i l a m e n t s , w h i c h a r e s i m i l a r t o t h e m y o f i l a m e n t s o f smooth m u s c l e ( R h o d i n , 1964; N e w s t e a d , 1 9 6 7 ) , f o u n d i n t h e p i l l a r c e l l s o f t h e r e s p i r -202 a t o r y l a m e l l a e may be s u g g e s t e d . I t i s p o s s i b l e t h a t c o n -t r a c t i o n o f t h e s e e l e m e n t s c o u l d i n some v/ay a l t e r t h e t e n s i o n o n t h e o v e r l y i n g e p i t h e l i u m and b a s a l l a m i n a t o r e d u c e t h e i r p e r m e a b i l i t y ; t h e known s t i m u l a t o r y a c t i o n o f n e u r o h y p o p h y s i a l p e p t i d e s on s m o o t h m u s c l e o f f e r s a p o s s i b l e m e d i a t i o n o f t h i s e f f e c t . V 203 LITERATURE C I T E D B a l l , J . N . 1969. P r o l a c t i n ( F i s h P r o l a c t i n o r P a r a l a c t i n ) and G r o w t h Hormone. I n : F i s h P h y s i o l o g y . V o l . I I . (W.S.Hoar and D . J . R a n d a l l , e d i t o r s ) , A c a d e m i c P r e s s I n c . , New Y o r k . B e n n i o n , G. 1968. The c o n t r o l o f t h e f u n c t i o n o f t h e h e a r t i n t e l e o s t f i s h . M.Sc. t h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , D e p t . o f Z o o l o g y . B e n t l e y , P . J . 1962. P e r m e a b i l i t y o f t h e s k i n o f t h e c y c l o s t o m e L a m p e t r a f l u v i a t i l i s t o w a t e r a n d e l e c t r o l y t e s . Comp. B i o c h e m . P h y s i o l . 6: 9 5 -97. B o e h l k e , K.W., O . W . T i e m e i e r , an d B . E . E l e f t h e r i o u . 1967. D i u r n a l r h y t h m i n p l a s m a e p i n e p h r i n e and n o r e p i n e p h r i n e i n t h e c h a n n e l c a t f i s h ( I c t a l u r u s p u n c t a t u s ) . Gen. Comp. E n d o c r i n o l . 8: 189-192. B o u r g u e t , J . , B . L a h l o u h , a n d J . M a e t z . 1964. M o d i f i c a t i o n s e x p e r i m e n t a l e s de l ' e q u i l i b r e h y d r o m i n e r a l e t osmo-r e g u l a t i o n c h e z C a r a s s i u s a u r a t u s . Gen. Comp. E n d o c r i n o l . 4: 563-576. _ _ _ _ B r e t t , J.R. 1962. Some c o n s i d e r a t i o n s i n t h e s t u d y o f r e s p i r -a t o r y m e t a b o l i s m i n f i s h , p a r t i c u l a r l y s a l m o n . J . F i s h . R e s . Bd. C a n a d a . 19: 1 0 2 5 - 1 0 3 8 . B r e t t , J.R. 1964. The r e s p i r a t o r y m e t a b o l i s m a n d swimming p e r f o r m a n c e o f y o u n g s o c k e y e s a l m o n . J . F i s h . R e s . B d . C a n a d a . 21: 1 183-1226. B r y a n , G.W. 1960. S o d i u m r e g u l a t i o n i n t h e c r a y f i s h A s t a c u s  f l u v i a t i l i s . I I . E x p e r i m e n t s w i t h s o d i u m - d e p l e t e d a n i m a l s . J . E x p . B i o l . 37: 1 00-112. C h e s t e r J o n e s , I . , D.K.O.Chan, I.W.Henderson, an d J . N . B a l i . 1969. The A d r e n o c o r t i c a l S t e r o i d s , A d r e n o c o r t i c o t r o p i n a n d t h e C o r p u s c l e s o f S t a n n i u s . I n : F i s h P h y s i o l o g y . V o l . I I . (W.S.Hoar an d D . J . R a n d a l l , e d i t o r s ^ , A c a d e m i c P r e s s I n c . , New Y o r k . C o n t e , F.P. 1969. S a l t S e c r e t i o n . I n : F i s h P h y s i o l o g y . V o l . I . (W.S.Hoar an d D . J . R a n d a l l , e d i t o r s ) , A c a d e m i c P r e s s I n c . , New Y o r k . C o n t e , F.P., H.H.Wagner, a n d T . O . H a r r i s . 1 9 6 3 . M e a s u r e m e n t s o f t h e b l o o d v o l u m e o f t h e f i s h Salmo g a i r d n e r i g a i r d n e r i . Am. J . P h y s i o l . 205: 533-540. D a i n t y , j . , a n d C.R.House. 1966. An e x a m i n a t i o n o f t h e e v i d -e n c e f o r membrane p o r e s i n f r o g s k i n . J . P h y s i o l . , L o n d o n . 185: 172-184. 204 D a t t a M u n s h i , J . S . , a n d S i n g h , B.N. 1968. On t h e m i c r o - c i r c u l -a t o r y s y s t e m o f t h e g i l l s o f c e r t a i n f r e s h w a t e r t e l e o s t e a n f i s h e s . J . Z o o l . ( L o n d o n ) . 154: 365-376. D a v i s , J . C . 1968. The i n f l u e n c e o f t e m p e r a t u r e an d a c t i v i t y o n c e r t a i n c a r d i o v a s c u l a r a n d r e s p i r a t o r y p a r a m e t e r s i n a d u l t s o c k e y e s a l m o n . M.Sc. t h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , D e p t . o f Z o o l o g y . D a v i s , J . C , a n d J.N.Cameron. 1970. W a t e r f l o w an d g a s e x c h a n g e a t t h e g i l l s o f r a i n b o w t r o u t , Salmo g a i r d n e r i . J . E x p . B i o l . I n p r e s s . D a v s o n , H. 1964. A T e x t b o o k o f G e n e r a l P h y s i o l o g y . T h i r d e d i t i o n . J . a n d A . C h u r c h i l l L t d . , L o n d o n . Dawson, J . B . , a n d F.W.Heaton. 1961 . The d e t e r m i n a t i o n o f m a g n e s i u m i n b i o l o g i c a l m a t e r i a l s by a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y . B i o c h e m . J . 80: 9 9 - 106. D o n a l d s o n , E.M., a n d J . R . M c B r i d e . 1 9 6 7 . The e f f e c t s o f h y p o -p h y s e c t o m y i n t h e r a i n b o w t r o u t Salmo g a i r d n e r i i ( R i c h . ) w i t h s p e c i a l r e f e r e n c e t o t h e p i t u i t a r y - i n t e r r e n a l a x i s . Gen. Comp. E n d o c r i n o l . 9: 9 3 - 1 0 1 . Duncan, D.B. 1955." " M u l t i p l e - r a n g e a n d m u l t i p l e F ~ t e s t s . ~ ' = B i o m e t r i c s . 11: 1-42. E nomoto, Y. 1 9 6 7 . On t h e e f f e c t s o f t h e s o m a t o t r o p i c hormone t o t h e u r i n e e l e c t r o l y t e s o f r a i n b o w t r o u t . B u l l . J a p a n . S o c . S c i . F i s h e r i e s . 33: 71-73. < E n s o r , D.M., a n d J . N . B a l l . 1968. P r o l a c t i n a n d f r e s h w a t e r s o d i u m f l u x e s i n P o e c i l i a l a t i p i n n a ( T e l e o s t e i ) . J . E n d o c r i n o l . 41: X V I . E v a n s , D.H. 1967. Sodium, c h l o r i d e , and w a t e r b a l a n c e o f t h e i n t e r t i d a l t e l e o s t , X i p h i s t e r a t r o p u r p u r e u s . I I I . The r o l e s o f s i m p l e d i f f u s i o n , e x c h a n g e d i f f u s i o n , o s m o s i s , a n d a c t i v e t r a n s p o r t . J . E x p . B i o l . 47: 525-534. E v a n s , D.H. 1969 a. S o d i u m , c h l o r i d e , a n d w a t e r b a l a n c e o f t h e i n t e r t i d a l t e l e o s t , P h o l i s g u n n e l l u s . J . E x p . B i o l . 50: 1 7 9 - 190. E v a n s , D.H. 1969 b . S t u d i e s on t h e p e r m e a b i l i t y t o w a t e r o f s e l e c t e d m a r i n e , f r e s h w a t e r an d e u r y h a l i n e t e l e o s t s . J . E x p . B i o l . 50: 6 8 9-703. F a r m e r , G . J . , a n d F.W.H.Beamish. 196 9 . O x y g e n c o n s u m p t i o n o f T i l a p i a n i l o t i c a i n r e l a t i o n t o swimming s p e e d a n d s a l i n i t y . J . F i s h . R e s . Bd. C a n a d a . 2 6 : 2 8 0 7 - 2 8 2 1 . F r a z i e r , H.S., E.F.Dempsey, and A . L e a f . 1962. Movement o f s o d i u m a c r o s s t h e m u c o s a l s u r f a c e o f t h e i s o l a t e d t o a d b l a d d e r and i t s m o d i f i c a t i o n b y v a s o p r e s s i n . J . Gen. P h y s i o l . 45: 5 2 9-543. 205 Fromm, P.O. 1 9 6 3 . S t u d i e s on r e n a l a n d e x t r a - r e n a l e x c r e t i o n i n a f r e s h - w a t e r t e l e o s t , Salmo g a i r d n e r i . Comp. B i o c h e m . P h y s i o l . 1 0: 12 1 - 1 2 8 . Fromm, P.O. 1968. Some q u a n t i t a t i v e a s p e c t s o f i o n r e g u l a t i o n i n t e l e o s t s . Comp. B i o c h e m . P h y s i o l . 27: 86 5 - 8 6 9 . F r y , F . E . J . 1 9 5 7 . T h e A q u a t i c R e s p i r a t i o n o f F i s h . I n : The P h y s i o l o g y o f t h e F i s h e s . V o l . I . (M.E.Brown, e d i t o r ) , A c a d e m i c P r e s s I n c . , New Y o r k . Gannon, B . J . , a n d G . B u r n s t o c k . 1 969. E x c i t a t o r y a d r e n e r g i c i n n e r v a t i o n o f t h e f i s h h e a r t . Comp. B i o c h e m . P h y s i o l . 29: 765-774. G a r c i a - R o m e u , F. a n d J . M a e t z . 1 9 6 4. The m e c h a n i s m o f s o d i u m a n d c h l o r i d e u p t a k e b y t h e g i l l s o f a f r e s h - w a t e r f i s h , C a r a s s u s a u r a t u s . I . E v i d e n c e f o r an i n d e p e n d e n t u p t a k e o f s o d i u m a n d c h l o r i d e i o n s . J . Gen. P h y s i o l . 47: 1 1 9 5 -1207. G a r c i a - R o m e u , F. a n d R . M o t a i s . 1 966. M i s e en e v i d e n c e d ' e c h a n g e s N a + / N H ^ + c h e z . 1 ' a n g u i l l e d ' e a u d o u c e , Comp. B i o c h e m . P h y s i o l . * 17: 1201-1204. Hammond, B.R. 1969. R e n a l f u n c t i o n and t h e e f f e c t s o f a r g i n i n e v a s o t o c i n i n l a k e t r o u t , S a l v e l i n u s n a m a y c u s h . Ph.D. t h e s i s , C o r n e l l U n i v e r s i t y , G r a d u a t e S c h o o l . H i c k m a n , C P . , J r . , a n d B.F.Trump. 1969. The K i d n e y . I n : F i s h  P h y s i o l o g y . V o l . I . (W.S.Hoar a n d D . J . R a n d a l l , e d i t o r s ) , A c a d e m i c P r e s s , I n c . , New Y o r k . H i l d e b r a n d t , J . , a n d A.C . Y o u n g . 1 9 6 5 . Anatomy a n d P h y s i c s o f R e s p i r a t i o n . I n : P h y s i o l o g y and B i o p h y s i c s . ( T . C . R u c h and H . D . P a t t o n , e d i t o r s ) , W.B. S a u n d e r s Company, P h i l a d e l p h i a . H o l m e s , R.M. 1 9 6 1 . K i d n e y f u n c t i o n i n m i g r a t i n g s a l m o n i d s . R e p t . C h a l l e n g e r S o c . ( C a m b r i d g e ) . 3: 23. H o l m e s , W.N. 1 9 5 9 . S t u d i e s on t h e h o r m o n a l c o n t r o l o f s o d i u m m e t a b o l i s m i n t h e r a i n b o w t r o u t ( S a l m o g a i r d n e r i ) . A c t a E n d o c r i n o l . 31: 587-602. H o l m e s , W.N., and D . G . B u t l e r . 1 963. The e f f e c t o f a d r e n o c o r t -i c a l s t e r o i d s on t h e t i s s u e e l e c t r o l y t e c o m p o s i t i o n o f f r e s h w a t e r r a i n b o w t r o u t ( S a l m o g a i r d n e r i ) . J . E n d o c r i n o l . 25: 457-464. H o l m e s , W.N. a n d I . M . S t a i n e r . 1 9 66. S t u d i e s on t h e r e n a l e x c r e t i o n o f e l e c t r o l y t e s b y t h e t r o u t ( S a l m o g a i r d n e r i ) . J . E x p . B i o l . 44: 33-46. H o u s e , C.R. 1963. O s m o t i c r e g u l a t i o n i n t h e b r a c k i s h w a t e r t e l e o s t , B l e n n i u s p h o l i s . J . E x p . B i o l . 40: 87-104. 206 H o u s t o n , A.H. 1 9 5 9 . O s m o r e g u l a t o r y a d a p t a t i o n o f s t e e l h e a d t r o u t ( S a l m o g a i r d n e r i R i c h a r d s o n ) t o s e a w a t e r . C a n . J . Z o o l . 37: 729-748. H o u s t o n , A.H. 1964. On p a s s i v e f e a t u r e s i n t h e o s m o r e g u l a t o r y a d a p t a t i o n o f anadramous s a l m o n i d s t o s e a w a t e r . J . F i s h . R e s . Bd. C a n a d a . 21: 1535-1538. H o u s t o n , A.H., a n d M.A. D e W i l d e . 1969. E n v i r o n m e n t a l t e m p e r -a t u r e a n d t h e b o d y f l u i d s y s t e m o f t h e f r e s h - w a t e r t e l e o s t - I I I . H e m a t o l o g y a n d b l o o d v o l u m e o f t h e r m a l l y a c c l i m a t e d b r o o k t r o u t , S a l v e l i n u s f o n t i n a l i s . Comp. B i o c h e m . P h y s i o l . 28: 877-885. H o u s t o n , A.H., M.A.DeWilde, a n d J.A.Madden. 1 9 6 9 . Some p h y s i o l o g i c a l c o n s e q u e n c e s o f a o r t i c c a t h e t e r i z a t i o n i n t h e b r o o k t r o u t ( S a l v e l i n u s f o n t i n a l i s ) . J . F i s h . R e s . Bd. C a n a d a . 26: 1847-1856. H o u s t o n , A.H., R . S . R e a v e s , J.A.Madden, and M.A. D e W i l d e . 1968. E n v i r o n m e n t a l t e m p e r a t u r e a n d t h e b o d y f l u i d s y s t e m o f t h f r e s h w a t e r t e l e o s t - I . I o n i c r e g u l a t i o n i n t h e r m a l l y a c c l i m a t e d r a i n b o w t r o u t , Salmo g a i r d n e r i . Comp. B i o c h e m . P h y s i o l . 25: 563 - 5 8 1 . H u g h e s , G.M. 1 9 6 6 . T h e d i m e n s i o n s o f f i s h g i l l s i n r e l a t i o n t o t h e i r f u n c t i o n . J . E x p . B i o l . 45: 17 7 - 1 9 5 . H u g h e s , G.M. a n d A . V . G r i m s t o n e . 1965. T h e f i n e s t r u c t u r e o f t h e s e c o n d a r y l a m e l l a e o f t h e g i l l s o f Gadus p o l l a c h i u s Q u a r t . J . M i c r . S c i . 106: 343-353. H u g h e s , G.M., a n d R . L . S a u n d e r s . 1970. R e s p o n s e s o f t h e r e s p -i r a t o r y pumps t o h y p o x i a i n t h e r a i n b o w t r o u t ( S a l m o  g a i r d n e r i ) . U n p u b l i s h e d m a n u s c r i p t . H u g h e s , G.M., a n d S h e l t o n , G. 1962. R e s p i r a t o r y m e c h a n i s m s an d t h e i r n e r v o u s c o n t r o l i n f i s h . A d v . Comp. B i o c h e m . P h y s i o l . 1: 275-364. Hunn, J . B . 1 9 6 9 . C h e m i c a l c o m p o s i t i o n o f r a i n b o w t r o u t u r i n e f o l l o w i n g a c u t e h y p o x i a s t r e s s . T r a n s . Am. F i s h . S o c . 98: 20-22. Hunn, J . B . , R . A . S c h o e t t g e r , a n d W . A . W i l l f o r d . 1 968. T u r n o v e r a n d u r i n a r y e x c r e t i o n o f f r e e a n d a c e t y l a t e d M.S. 222 b y r a i n b o w t r o u t , Salmo g a i r d n e r i . J . F i s h . R e s . Bd. C a n a d a . 25: 2 5 - 3 1 . Hunn, J . B . , a n d W . A . W i l l f o r d . 1 9 7 0. The e f f e c t o f a n e s t h e t i z -a t i o n and u r i n a r y b l a d d e r c a t h e t e r i z a t i o n on r e n a l f u n c t i o n o f r a i n b o w t r o u t . Comp. B i o c h e m . P h y s i o l . 33: 805-812. K e r s t e t t e r , T.H., L . B . K i r s c h n e r , and D . D . R a f u s e . 1970. On t h e me c h a n i s m s o f N a ^ t r a n s p o r t b y t h e i r r i g a t e d g i l l s o f r a i n b o w t r o u t ( S a l m o g a i r d n e r i ) . U n p u b l i s h e d m a n u s c r i p t . 207 K e y s , A. a n d J . B . B a t e m a n . 1932. B r a n c h i a l r e s p o n s e s t o a d r e n a l i n e a n d p i t r e s s i o n i n t h e e e l . J . P h y s i o l . , L o n d o n . 75: 327-336. K i r s c h n e r , L . B . 1955. On t h e m e c h a n i s m o f a c t i v e s o d i u m t r a n s p o r t a c r o s s f r o g s k i n . J . C e l l . Comp. P h y s i o l . 45: 6 1 - 8 7 . K i r s c h n e r , L . B . 1 9 6 9 . V e n t r a l a o r t i c p r e s s u r e a n d sodium f l u x e s i n p e r f u s e d e e l g i l l s . Am. J . P h y s i o l . 217: 596-604. K i r s c h n e r , L . B . 1970. The s t u d y o f N a C l t r a n s p o r t i n a q u a t i c a n i m a l s . Am. Z o o l o g i s t . ' 10: 365-376. K l o n t z , G.W., and L . S . S m i t h . 1 968. M e t h o d s o f U s i n g F i s h a s B i o l o g i c a l R e s e a r c h S u b j e c t s . I n : M e t h o d s o f A n i m a l  E x p e r i m e n t a t i o n . V o l . I I I . A c a d e m i c P r e s s I n c . , New Y o r k . K r a m e r , C.Y. 1956. E x t e n s i o n o f m u l t i p l e r a n g e t e s t s t o g r o u p means w i t h u n e q u a l numbers o f r e p l i c a t i o n s . B i o m e t r i c s 12: 307-310. Krawkow, N.P. 1913. U b e r d i e ' W i r k u n g v o n G x f t e n a u f d i e g e f a s s e i s o l i e r t e r F i s c h k i e m e n . _ A r c h . G e s . P h y s i o l . 1 5 1 : 583-_603. K r o g h , A. 1 9 4 1 . The C o m p a r a t i v e P h y s i o l o g y o f R e s p i r a t o r y  M e c h a n i s m s . U n i v . o f P e n n s y l v a n i a P r e s s , P h i l a d e l p h i a . L a h l o u , B., a n d A . G i o r d a n . 1 9 7 0. L e c o n t r S l e h o r m o n a l d e s e c h a n g e s e t de l a b a l a n c e de l ' e a u c h e z l e t e l e o s t e e n d ' e a u d o u c e C a r a s s i u s a u r a t u s . i n t a c t e t h y p o p h y s e c t o m i s e . Gen. Comp. E n d o c r i n o l . 14: 491-509. L a h l o u , B., I.W.Henderson, a n d W.H.Sawyer. 1969. Sod i u m e x -c h a n g e s i n g o l d f i s h ( C a r a s s i u s a u r a t u s . L . ) a d a p t e d t o a h y p e r t o n i c s a l i n e s o l u t i o n . Comp. B i o c h e m . P h y s i o l . 28: 1 4 2 7 - 1 4 3 3 . L a h l o u , B., and W.H.Sawyer. 1969. E l e c t r o l y t e b a l a n c e i n h y p o -p h y s e c t o m i z e d g o l d f i s h , C a r a s s i u s a u r a t u s L . Gen. Comp. E n d o c r i n o l . 12: 370-377. L e d e r i s , K. 1 970. T e l e o s t u r o p h y s i s . I . B i o a s s a y o f an a c t i v e u r o p h y s i a l p r i n c i p l e on t h e i s o l a t e d u r i n a r y b l a d d e r o f t h e r a i n b o w t r o u t , Salmo g a i r d n e r i . Gen. Comp. E n d o c r i n o l . 14: '417-426. L i n e w e a v e r , H., a n d D . B u r k e . 1934. The d e t e r m i n a t i o n o f enzyme-d i s s o c i a t i o n c o n s t a n t s . J . Am. Chem. S o c . 56: 658. Mackay, W.C., and D . D . B e a t t y . 1968. The e f f e c t o f t e m p e r a t u r e o n r e n a l f u n c t i o n i n t h e w h i t e s u c k e r f i s h , C a t o s t o m u s  c o m m e r s o n i i . Comp. B i o c h e m . P h y s i o l . 26: 2 35-245. M a e t z , J . 1956. L e s e c h a n g e s de s o d i u m c h e z l e p o i s s o n C a r a s s i u s a u r a t u s L . A c t i o n d'un i n h i b i t e u r de l ' a n h y d r a s e c a r b o n i q u e . J . P h y s i o l . , P a r i s . 48: 108 5 - 1 0 9 9 . 208 M a e t z , J . 1 9 6 9 . S e a w a t e r t e l e o s t s : e v i d e n c e f o r a s o d i u m -p o t a s s i u m e x c h a n g e i n t h e b r a n c h i a l s o d i u m - e x c r e t i n g pump. N a t u r e . 166: 613 - 6 1 5 . M a e t z , J . , J . B o u r g u e t , a n d B . L a h l o u . 1964 a. U r o p h y s e e t osmo-r e g u l a t i o n c h e z C a r s s i u s a u r a t u s . Gen. C o m p . E n d o c r i n o l . 4: 401-414. M a e t z , J . , J . B o u r g u e t , B . L a h l o u , a n d J . H o u d r y . 1964 b . P e p t i d e s n e u r o h y p o p h y s a i r e s e t o s m o r e g u l a t i o n c h e z C a r a s s i u s a u r a t u s . Gen. Comp. E n d o c r i n o l . 4: 508-522. M a e t z , J . , a n d F . G a r c i a - R o m e u . 1964. The me c h a n i s m o f s o d i u m a n d c h l o r i d e u p t a k e b y t h e g i l l s o f a f r e s h - w a t e r f i s h , C a r a s s i u s a u r a t u s . I I . E v i d e n c e f o r N H 4 + / N a + a n d HC0~/C1~ e x c h a n g e s . J . Gen. P h y s i o l . 47: 1209-1227. M a e t z , J . , a n d M . J u l i e n . 1 9 6 1 . A c t i o n o f n e u r o h y p o p h y s e a l h o r m o n e s on t h e s o d i u m f l u x e s o f a f r e s l w a t e r t e l e o s t . N a t u r e . 189: 15 2 - 1 5 3 . M a e t z , J . , N.Mayer, a n d M . M . C h a r t i e r - B a r a d u c . 1967 a . L a b a l a n c e m i n e r a l e du s o d i u m c h e z A n g u i l l a a n g u i l l a en e a u de mer,en •-• e a u d o u c e e t au c o u r s de t r a n s f e r t d'un m i l i e u a l ' a u t r e : _ E f f e t s de 1 • h y p o p h y s e c f e e m i e e t de l a p r o l a c t i n e . G e n r - -Comp. E n d o c r i n o l . 8: 177-188. M a e t z , J.,W.H.Sawyer, G . E . P i c k f o r d , a n d N.Mayer. 1967 b . E v o l u t i o n de l a b a l a n c e m i n e r a l e du s o d i u m c h e z F u n d u l u s  h e t e r o c l i t u s au c o u r s du t r a n s f e r t d ' e a u de mer en e a u d o u c e : E f f e t s de 1 • h y p o p h y s e c t o m i e e t de l a p r o l a c t i n e . Gen. Comp. E n d o c r i n o l . 8: 16 3-176. M a n e r y , J . F . 2954. W a t e r a n d e l e c t r o l y t e m e t a b o l i s m . P h y s i o l . R e v. 34: 334-417. M a y e r , N., J . M a e t z , D.K.O.Chan, M . E . F o r s t e r , a n d I . C h e s t e r J o n e s . 1 9 6 7 . C o r t i s o l , a s o d i u m e x c r e t i n g f a c t o r i n t h e e e l ( A n g u i l l a a n g u i l l a L.) a d a p t e d t o s e a w a t e r . N a t u r e . 214: 1 118-1120. M a y e r , N. a n d J . N i b e l l e . 1 9 69. Sodi u m s p a c e i n f r e s h - w a t e r a n d s e a - w a t e r e e l s . Comp. B i o c h e m . P h y s i o l . 31: 589-597. M a y e r , N., and J . N i b e l l e . 1 970. K i n e t i c s o f t h e m i n e r a l b a l a n c e i n t h e e e l A n g u i l l a a n g u i l l a i n r e l a t i o n t o e x t e r n a l s a l -i n i t y c h a n g e s a n d i n t r a v a s c u l a r s a l i n e i n f u s i o n s . Comp. B i o c h e m . P h y s i o l . 35: 553-566. M i l e s , H.M., and L . S . S m i t h . 1968. I o n i c r e g u l a t i o n i n m i g r a t -i n g j u v e n i l e c o h o s a l m o n , O n c h o r h y n c u s k i s u t c h . Comp. B i o c h e m . P h y s i o l . 26: 381-398. M o r r i s , R., a n d J . M . B u l l . 1 968. S t u d i e s on f r e s h - w a t e r osmo-r e g u l a t i o n i n t h e ammocoete l a r v a o f L a m p e t r a p l a n e r i ( B l o c h ) . I I . T h e e f f e c t o f d e - i o n i z e d w a t e r a n d t e m p e r a t u r e on s o d i u m b a l a n c e . J . E x p . B i o l . 48: 597-609. 209 M o r r i s , R.,.and J . M . B u l l . 1970. S t u d i e s o n f r e s h - w a t e r osmo-r e g u l a t i o n i n t h e ammocoete l a r v a o f L a m p e t r a p l a n e r i ( B l o c h ) . I I I . The e f f e c t o f e x t e r n a l and i n t e r n a l s o d i u m c o n c e n t r a t i o n on s o d i u m t r a n s p o r t . J . E x p . B i o l . 5 2:275-290. M o t a i s , R. 1967. L e s m e c a n i s m e s d ' e c h a n g e s i o n i q u e s b r a n c h i a u x c h e z l e s T e l e o s t e e n s . Ann. I n s t . O c e a n . P a r i s . 45: 1-83. M o t a i s , R., F . G a r c i a - R o m e u , and J . M a e t z . 1966. E x c h a n g e d i f f -u s i o n e f f e c t and e u r y h a l i n i t y i n t e l e o s t s . J . Gen. P h y s i o l . 50: 391-422. M o t a i s , R., and J . M a e t z , 1964. A c t i o n s d e s hormones n e u r o h y p o -p h y s a i r e s s u r l e g 'echanges de s o d i u m ( M e s u r e s a l ' a i d e du r a d i o - s o d i u m Na "chez un t e l e o s t e e n e u r y h a l i n : P l a t i c h t h y s  f l e s u s L . Gen. Comp. E n d o c r i n o l . 4: 210-224. M o t t , J . C . 1 9 5 1 . Some f a c t o r s a f f e c t i n g t h e b l o o d c i r c u l a t i o n i n t h e common e e l ( A n g u i l l a a n g u i l l a ) . J . P h y s i o l . , L o n d o n . 114: 387-398. M u i r , B.S. 1968. G i l l d i m e n s i o n s as a f u n c t i o n o f f i s h s i z e . J . F i s h . R e s . Bd. C a n a d a . 26: 165-170. - . M u i r , B.S. 1970. C o n t r i b u t i o n t o t h e s t u d y o f b l o o d p a t h w a y s — - i n t e l e o s t g i l l s , - e o p e r n . 1970 ( 1 ) : 1 9 -28. _ ^ ~ M u i r , B.S. a n d J . I . K e n d a l l . 1968. S t r u c t u r a l m o d i f i c a t i o n s i n t h e g i l l s o f t u n a s a n d some o t h e r o c e a n i c f i s h e s . C o p e i a . 1968 ( 2 ) : 388-398. Nakano, T., a n d N . T o m l i n s o n . 1967. C a t e c h o l a m i n e a n d c a r b o h y d r a t e m e t a b o l i s m i n r a i n b o w t r o u t (Salmo g a i r d n e r i ) i n r e l a t i o n t o p h y s i c a l d i s t u r b a n c e . J . F i s h . R e s . B d . C a n a d a . 24: 1 7 0 1 - 1 7 1 5 . N e w s t e a d , J.D. 1 9 6 7 . F i n e s t r u c t u r e o f t h e r e s p i r a t o r y l a m e l l a e o f t e l e o s t e a n g i l l s . Z e i t s c h r i f t f u r Z e l l f o r s c h u n g . 79: 396-428. O s t l u n d , E . 1954. The d i s t r i b u t i o n o f c a t e c h o l a m i n e s i n l o w e r a n i m a l s a n d t h e i r e f f e c t on t h e h e a r t . A c t a . P h y s i o l . S c a n d . 31: S u p p l . 112. O s t l u n d , E . , a n d R . F a n g e . 1962. V a s o d i l a t i o n b y a d r e n a l i n a n d n o r a d r e n a l i n e , and t h e e f f e c t s o f some o t h e r s u b s t a n c e s on p e r f u s e d f i s h g i l l s . Comp. B i o c h e m . P h y s i o l . 5: 307-309. P a c k e r , R.K., a n d W.A.Dunson. 1970. E f f e c t s o f l o w e n v i r o n m e n t a l pH on b l o o d pH a n d s o d i u m b a l a n c e o f b r o o k t r o u t . J . E x p . Z o o l . 174: 65-72. P a p p e n h e i m e r , J.R. 1953. P a s s a g e o f m o l e c u l e s t h r o u g h c a p i l l a r y w a l l s . P h y s i o l . Rev. 33: 387-423. P e r k s , A.M. 1969. The N e u r o h y p o p h y s i s . I n : F i s h P h y s i o l o g y . V o l . 1 1 . (W.S.Hoar and D . J . R a n d a l l , e d i t o r s ) , A c a d e m i c P r e s s I n c . , New Y o r k . 210 P l e h n , M. 1 9 0 1 . Zum f e i n e r e n B au d e r F i s c h k e i m e . Z o o l . A n z . 24: 4 3 9 - 4 4 3 . P o t t s , W.T.W., a n d E v a n s , D.H. 1967. Sodium a n d c h l o r i d e b a l a n c e i n t h e k i l l i f i s h F u n d u l u s h e t e r o c l i t u s . B i o l . B u l l . 1 3 3: 411-424. P o t t s , W.T.W., and W . R . F l e m i n g . 1 9 70. The e f f e c t s o f p r o l a c t i n a n d d i v a l e n t i o n s o n t h e p e r m e a b i l i t y t o w a t e r o f F u n d u l u s  k a n s a e . J . E x p . B i o l . 53: 317-327. P o t t s , W.T.W., M . A . F o s t e r , a n d J . W . S t a t h e r . 1970. S a l t a n d w a t e r b a l a n c e i n s a l m o n s m o l t s . J . E x p . B i o l . 52: 553-564. R a n d a l l , D.J. 1970 a. Gas E x c h a n g e . i n F i s h . I n : F i s h P h y s i o l o g y . V o l . IV..(W.S.Hoar a n d D . J . R a n d a l l , e d i t o r s ) , A c a d e m i c P r e s s I n c . , New Y o r k . R a n d a l l , D.J. 1970 b . The C i r c u l a t o r y S y s t e m . I n : F i s h P h y s i - o l o g y . V o l . I V . (W.S.Hoar and D . J . R a n d a l l , e d i t o r s ) , A c a d e m i c P r e s s I n c . , New Y o r k . R a n d a l l , D.J., D.Baumgarten-Schumman and M . M a l y u s z . 1 9 6 9 . Gas e x c h a n g e v e r s u s i o n e x c h a n g e a c r o s s t h e g i l l s o f f i s h e s . U n p u b l i s h e d m a n u s c r i p t . R a n d a l l , D.J., G . F . H o l e t o n , a n d E . D . S t e v e n s . 1967. T he e x c h a n g e o f o x y g e n a n d c a r b o n d i o x i d e a c r o s s t h e g i l l s o f r a i n b o w t r o u t . J . E x p . B i o l . 46: 339-348. R a n d a l l , D . J i , a n d L . S . S m i t h . 1967. The e f f e c t o f e n v i r o n m e n t a l f a c t o r s o n c i r c u l a t i o n a nd r e s p i r a t i o n i n t e l e o s t f i s h . H y d r o b i o l o g i a 19: 113-124. R a n d a l l , D.J., and E . D . S t e v e n s . 1 9 6 7 . T he r o l e o f a d r e n e r g i c r e c e p t o r s i n c a r d i o v a s c u l a r c h a n g e s a s s o c i a t e d w i t h e x e r c i s e i n s a l m o n . Comp. B i o c h e m . P h y s i o l . 21: 415-424. Rao, G.M.M. 1968. O x y g e n c o n s u m p t i o n o f r a i n b o w t r o u t ( S a l m o  g a i r d n e r i ) i n r e l a t i o n t o a c t i v i t y a nd s a l i n i t y . C a n . J . Z o o l . 46: 781-786. Rao, G.M.M. 1969. E f f e c t o f a c t i v i t y , s a l i n i t y , a n d t e m p e r a t u r e on p l a s m a c o n c e n t r a t i o n s o f r a i n b o w t r o u t . C a n . J . Z o o l . 47: 131-134. R h o d i n , J.A.G. 1964. S t r u c t u r e o f t h e g i l l s o f t h e m a r i n e f i s h p o l l a c k ( P o l l a c h i u s v i r e n s ) . A n a t . R e c . 148: 420. R i c h a r d s , B„D., a n d P.O.Fromm. 1969. P a t t e r n s o f b l o o d f l o w t h r o u g h f i l a m e n t s a nd l a m e l l a e o f i s o l a t e d - p e r f u s e d r a i n -bow t r o u t ( S a l m o g a i r d n e r i ) g i l l s . Comp. B i o c h e m . P h y s i o l . 29; 1063-1070. R i c h a r d s , B.D., a n d P.O.Fromm. 1970. Sodium u p t a k e b y i s o l a t e d -p e r f u s e d g i l l s o f r a i n b o w t r o u t ( S a l m o g a i r d n e r i ) . Comp. B i o c h e m . P h y s i o l . 33: 303-310. 211 R i e s s , J . A . 1 8 8 1 . Der Bau d e r K e i m e n b l a t e r b e i d e n K n o c h e n f i s c h e n . A r c h . N a t u r g e s h . 47, I : 518-550. R u s s e l , J . A . 1965. The A d r e n a l s . I n : P h y s i o l o g y a n d B i o p h y s i c s . ( T . C . R u c h a n d H . D . P a t t o n , e d i t o r s ) , W.B.Saunders Company, P h i l a d e l p h i a . S a g e , M. 1968. R e s p o n s e s t o o s m o t i c s t i m u l i o f X i p h o p h o r u s p r o l a c t i n c e l l s i n o r g a n c u l t u r e . Gen. Comp. E n d o c r i n o l . 10: 70-74. S a u n d e r s , R.L. 1962. The i r r i g a t i o n o f t h e g i l l s i n f i s h e s . I I . E f f i c i e n c y o f o x y g e n u p t a k e i n r e l a t i o n t o r e s p i r -a t o r y f l o w , a c t i v i t y a nd c o n c e n t r a t i o n s o f o x y g e n a n d c a r b o n d i o x i d e . C a n . J . Z o o l . 40: 817-862. Shaw, J . 1959. The a b s o r p t i o n o f s o d i u m i o n s b y t h e c r a y f i s h , A s t a c u s p a l l i p e s L e r e b o u l l e t . I . The e f f e c t o f e x t e r n a l a n d i n t e r n a l s o d i u m c o n c e n t r a t i o n s . J . E x p . B i o l . 36: 1 26-144. S h e h a d e h , Z.H., a n d M.S.Gordon. 1969. The r o l e o f t h e i n t e s t i n e i n s a l i n i t y a d a p t a t i o n o f t h e r a i n b o w t r o u t , Salmo g a i r d n e r i . Comp. B i o c h e m . P h y s i o l . 30: 397-418. S m i t h , L . S . 1966. B l o o d v o l u m e o f t h r e e s a l m o n i d s . J . F i s h . R e s . Bd. C a n a d a . 23: 1439-1446. S m i t h , L . S . , a n d G . R . B e l l . 1964. A t e c h n i q u e f o r p r o l o n g e d b l o o d s a m p l i n g i n f r e e - s w i m m i n g s a l m o n . J . F i s h . R e s . Bd. C a n a d a . 21: 711-717. S m i t h , L . S . , J . R . B r e t t , and J . C . D a v i s . 1 967. C a r d i o v a s c u l a r d y n a m i c s i n swimming a d u l t s o c k e y e s a l m o n . J . F i s h . R e s . Bd. C a n a d a . 24: 17 7 5 - 1 7 9 0 . S t e e n , J . B . , a n d A . K r u y s s e . 1964. The r e s p i r a t o r y f u n c t i o n o f t e l e o s t e a n g i l l s . Comp. B i o c h e m . P h y s i o l . 12: 127-142. S t e v e n s , E.D., 1968 a . The e f f e c t o f e x e r c i s e on t h e d i s t r i b -u t i o n o f b l o o d t o v a r i o u s o r g a n s i n r a i n b o w t r o u t . Comp. B i o c h e m . P h y s i o l . 25: 615-625. S t e v e n s , E.D. 1968 b . C a r d i o v a s c u l a r d y n a m i c s d u r i n g swimming i n f i s h , p a r t i c u l a r l y r a i n b o w t r o u t ( S a l m o g a i r d n e r i ) . Ph.D. t h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , D e p t . o f Z o o l o g y . S t e v e n s , E.D., a n d D . J . R a n d a l l . 1967 a. C h a n g e s i n b l o o d p r e s s u r e , h e a r t r a t e , a n d b r e a t h i n g r a t e d u r i n g m o d e r a t e swimming a c t i v i t y i n r a i n b o w t r o u t . J . E x p . B i o l . 46: 307-315. S t e v e n s , E.D., and D . J . R a n d a l l . 1967 b . C h a n g e s o f g a s c o n -c e n t r a t i o n s i n b l o o d and w a t e r d u r i n g m o d e r a t e swimming a c t i v i t y i n r a i n b o w t r o u t . J . E x p . B i o l . 46: 329-337. 2 1 2 S u t c l i f f e , D . W . , a n d J.Shaw. 1968. Sodium r e g u l a t i o n i n t h e a m p h i p o d Gammarus d u e b e n i L i l l j e b o r g f r o m f r e s h - w a t e r l o c a l i t i e s i n I r e l a n d . J . E x p . B i o l . 48: 339-358. T a y l o r , W . , A . H . H o u s t o n , a n d J . D . H o r g a n . 1968. D e v e l o p m e n t o f a c o m p u t e r m o d e l s i m u l a t i n g some a s p e c t s o f t h e c a r d i o v a s c u l a r - r e s p i r a t o r y d y n a m i c s o f t h e s a l m o n i d f i s h . J . E x p . B i o l . 49: 477-494. T e l o h , H.A. 1958. E s t i m a t i o n o f se r u m c a l c i u m b y f l a m e p h o t o -m e t r y . A.M.A. A r c h i v e s o f P a t h o l o g y . 66: 474 - 4 8 1 . Toews, D.P. 1966. The e f f e c t o f c y c l i n g t e m p e r a t u r e s on e l e c t r o l y t e b a l a n c e i n s k e l e t a l m u s c l e and p l a s m a o f r a i n b o w t r o u t , Salmo g a i r d n e r i . M.Sc. t h e s i s . U n i v e r s i t y o f A l b e r t a , D e p t . o f Z o o l o g y . Toews, D.P., a n d C . P . H i c k m a n . 1969. The e f f e c t o f c y c l i n g t e m p e r a t u r e s on e l e c t r o l y t e b a l a n c e i n s k e l e t a l m u s c l e a n d p l a s m a o f r a i n b o w t r o u t Salmo g a i r d n e r i . Comp. B i o c h e m . P h y s i o l . 29: 905-918. U s s i n g , H.H. 1949 a . The d i s t i n c t i o n b y means o f t r a c e r s b e t w e e n a c t i v e t r a n s p o r t a n d d i f f u s i o n . A c t a . P h y s . S c a n d . - - 1 9 : 43-56. — • — - ~~ ' U s s i n g , H.H. 1949 b . The a c t i v e i o n t r a n s p o r t t h r o u g h t h e i s o l a t e d f r o g s k i n i n t h e l i g h t o f t r a c e r s t u d i e s . A c t a . P h y s . S c a n d . 17: 1-37. v o n E u l e r , U.S., a n d R . F a n g e . 1961., C a t e c h o l a m i n e s i n n e r v e s a n d o r g a n s o f M y x i n e g l u t i n o s a , S q u a l u s a c a n t h i a s a n d Gadus c a l l i a r i a s . Gen. Comp. E n d o c r i n o l . 1: 191-194. W a i t z e n e g g e r , M . 1 9 6 7 . I n f l u e n c e d e s a m i n e s b i o g e n e s s u r l a m e c a n i q u e o p e r c u l a i r e d'un t e l e o s t e e n : l a c a r p e commune ( C y p r i n u s c a r p i o L . ) . J . P h y s i o l . , P a r i s . 59: 351-356. Wedemeyer, G., a n d K . C h a t t e r t o n . 1970. Some b l o o d c h e m i s t r y v a l u e s f o r t h e r a i n b o w t r o u t ( S a l m o g a i r d n e r i ) . J . F i s h . R e s . B d. C a n a d a . 27: 1162-1164. W o l f , K. 1 9 6 3 . P h y s i o l o g i c a l s a l i n e s f o r f r e s h w a t e r t e l e o s t s . P r o g r v . F i s h . C u l t . 25: 135-140. Wood, C M . a n d D J . R a n d a l l . 1 971. The e f f e c t o f a n a e m i a on i o n e x c h a n g e i n t h e s o u t h e r n f l o u n d e r ( P a r a l i c h t h y s  l e t h o s t i g m a ) . Comp. B i o c h e m . P h y s i o l . I n p r e s s . Woodbury, D.M. 1 9 6 5 . P h y s i o l o g y o f Body F l u i d s . I n : P h y s i -o l o g y and B i o p h y s i c s . ( T . C . R u c h and H . D . P a t t o n , e d i t o r s ) , W . B.Saunders Company, P h i l a d e l p h i a . Woodbury, J . W . 1965. The C e l l Membrane: I o n i c and P o t e n t i a l G r a d i e n t s a n d A c t i v e t r a n s p o r t . I n : P h y s i o l o g y and B i o - p h y s i c s ( T . C . R u c h a n d H . D . P a t t o n , e d i t o r s ) , W . B . S a u n d e r s Company, P h i l a d e l p h i a . 

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