Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Factors affecting swimbladder volume in rainbow trout (Salmo gairdneri) held in gas suppersaturated water Shrimpton, James Mark 1987

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1988_A6_7 S47.pdf [ 3.03MB ]
Metadata
JSON: 831-1.0097852.json
JSON-LD: 831-1.0097852-ld.json
RDF/XML (Pretty): 831-1.0097852-rdf.xml
RDF/JSON: 831-1.0097852-rdf.json
Turtle: 831-1.0097852-turtle.txt
N-Triples: 831-1.0097852-rdf-ntriples.txt
Original Record: 831-1.0097852-source.json
Full Text
831-1.0097852-fulltext.txt
Citation
831-1.0097852.ris

Full Text

FACTORS AFFECTING SWIMBLADDER VOLUME IN RAINBOW TROUT CSALMO GAIRDNERI) HELD IN GAS SUPERSATURATED WATER By JAMES MARK SHRIMPTON B.Sc.CHonours), University of V i c t o r i a , 198S A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES CDepartment of Zoology) We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December 1987 ® J. MARK SHRIMPTON, 1987 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 D a t e D f c t L . 5 \Ofifl DF-fin/ft-n i i ABSTRACT I examined t h e r e s p o n s e o f t h e rainbow t r o u t . CSalmo g a i r d n e r i J swimbladder bo gas s u p e r s a t u r a t e d water. Cannulas p o s i t i o n e d i n t h e swimbladder o f f i s h were c o n n e c t e d t o a p r e s s u r e t r a n s d u c e r , f a c i l i t a t i n g d i r e c t measurement o f swimbladder p r e s s u r e . F i s h h e l d i n s u p e r s a t u r a t e d water showed an i n c r e a s e i n swimbladder p r e s s u r e . The r e s p o n s e showed a s t r o n g dependence on t h e t o t a l gas p r e s s u r e and t h e oxygen p a r t i a l p r e s s u r e o f t h e water. The minimum l e v e l o f gas s u p e r s a t u r a t i o n o b s e r v e d t o cause t h i s r e s p o n s e was a AP o f 27 mmHg C P O 2 = IdO mmHg). Swimbladder p r e s s u r e i n c r e a s e d u n t i l gas was f o r c e d o u t t h e pneumatic du c t . The pneumatic d u c t r e l e a s e p r e s s u r e i s s i z e dependent, w i t h g r e a t e r p r e s s u r e r e q u i r e d t o e x p e l swimbladder gas i n s m a l l e r f i s h . The e x p a n s i o n o f t h e swimbladder due t o i n c r e a s e d p r e s s u r e c a u s e s a d e c r e a s e i n d e n s i t y . The buoyant f o r c e c r e a t e d by d e c r e a s e d d e n s i t y i s g r e a t e s t f o r f i s h below lOg. These f i s h seek depth t o compensate f o r swimbladder o v e r i n f l a t i o n . i i i TABLE OF CONTENTS PAGE A b s t r a c t i i L i s t o f T a b l e s i v L i s t o f F i g u r e s v Acknowledgements v i i 1.0 I n t r o d u c t i o n 1 2.0 Methods and M a t e r i a l s 11 2.1 P r o d u c t i o n o f S u p e r s a t u r a t i o n and Water A n a l y s i s 11 2.2 D e t e r m i n a t i o n o f Swimbladder I n f l a t i o n T h r e s h o l d 13 2.3 D e t e r m i n a t i o n o f Pneumatic Duct R e l e a s e P r e s s u r e 15 2.3.1 D i r e c t Measurement o f Pneumatic Duct R e l e a s e 16 P r e s s u r e 2.3.2 I n d i r e c t Measurement o f Pneumatic Duct R e l e a s e 16 P r e s s u r e 2.4 Swimbladder E x p a n s i o n 19 2.5 B e h a v i o u r a l E x p e r i m e n t s 21 3.0 R e s u l t s 24 3.1 Response o f Swimlbadder t o Gas S u p e r s a t u r a t e d Water 24 3.2 Pneumatic Duct R e l e a s e P r e s s u r e 35 3.3 Swimbladder E x p a n s i o n 39 3.4 B e h a v i o u r a l Response 44 4.0 D i s c u s s i o n 48 5.0 Summary 59 6.0 L i t e r a t u r e C i t e d 60 i v LIST OF TABLES TABLE PAGE 1 S t a t i s t i c s f o r r e g r e s s i o n o f r a t e o f swimbladder 33 i n f l a t i o n on d i s s o l v e d gas t e n s i o n f o r f i v e l e v e l s o f P 0 o V LIST OF FIGURES FIGURE PAGE 1 Diagram o f a p p a r a t u s used i n t h e measurement o f 14 swimbladder p r e s s u r e f o r f i s h h e l d i n a i r s u p e r s a t u r a t e d water 2 A p p a r a t u s used t o measure t h e p r e s s u r e w i t h i n 17 th e swimbladder r e q u i r e d t o f o r c e gas o u t t h e pneumatic d u c t f o r f i s h l e s s t h a n 50g 3 Diagram o f t h e o b s e r v a t i o n column used t o 22 mo n i t o r t h e depth d i s t r i b u t i o n o f t h e f i s h f o r d i f f e r e n t l e v e l s o f TGP 4 I n c r e a s e i n swimbladder p r e s s u r e f o r a 195g 25 f i s h h e l d i n gas s u p e r s a t u r a t e d water CAP = 50 mmHg) 5 V e n t i n g o f gas o u t t h e pneumatic d u c t when a i r 26 was i n f u s e d i n t o t h e swimbladder 6 I n c r e a s e i n swimbladder p r e s s u r e f o r a 184g 28 f i s h h e l d i n gas s u p e r s a t u r a t e d water CAP = 29 mmHg) 7 R e l e a s e o f gas o u t t h e pneumatic d u c t d u r i n g 29 i n f u s i o n o f a i r i n t o t h e swimbladder 8 Rate o f i n c r e a s e i n swimbladder p r e s s u r e f o r f i s h 31 h e l d i n d i f f e r e n t l e v e l s o f gas s u p e r s a t u r a t e d water 9 P l o t o f TGP t h r e s h o l d C F i d l e r , 1985) and swim- 36 b l a d d e r i n f l a t i o n d a t a as a f u n c t i o n o f P O 2 10 Pneumatic d u c t r e l e a s e p r e s s u r e as a f u n c t i o n 37 o f f i s h w e i g h t 11 Pneumatic d u c t r e l e a s e p r e s s u r e as a f u n c t i o n 38 o f f i s h w e i g h t p l o t t e d l o g a r i t h m i c a l l y 12 R e l a t i o n s h i p between t h e p r e s s u r e and volume o f t h e swimbladder f o r a 9.5g rainbow t r o u t 41 D e n s i t y o f rainbow t r o u t a t DRP as a f u n c t i o n o f f i s h w e i g h t L i f t f a c t o r c a l c u l a t e d a t DRP as a f u n c t i o n o f f i s h w e i g h t Depth d i s t r i b u t i o n f o r rainbow t r o u t as a f u n c t i o n o f TGP and f i s h w e i g h t ACKNOWLEDGEMENTS I am gratef u l to several individuals, who generously gave of t h e i r time and expertise toward the completion of t h i s thesis. In p a r t i c u l a r , I thank Dr. Dave Randall f o r h i s support and h e l p f u l c r i t i c i s m of t h i s project. I extend my appreciation to Mr. Larry F i d l e r , f o r h i s guidance and assistance throughout the study. I thank Mr. Jon Jensen, of the P a c i f i c B i o l o g i c a l Station, Nanaimo, B.C., f o r advice and f o r the loan of a tensionometer and the observation column. Review of the thesis by Dr. Malcolm Shrimpton i s g r a t e f u l l y acknowledged. F i n a l l y , I thank my wife J u l i e , f o r her help and encouragement. 1 1.0 INTRODUCTION F i s h exposed t o water s u p e r s a t u r a t e d w i t h a t m o s p h e r i c gases can d e v e l o p a p h y s i c a l l y i n d u c e d syndrome c a l l e d Gas Bubble Trauma CGBT), where gas b u b b l e s form i n t h e b l o o d and o t h e r t i s s u e s o f t h e f i s h CPauley and N a k a t a n i , 1967). The c o n d i t i o n was f i r s t r e c o g n i z e d by Marsh and Gorham C1905), and can be l e t h a l t o a q u a t i c a n i m a l s . A f t e r t h i s i n i t i a l r e s e a r c h , d i s s o l v e d gas s u p e r s a t u r a t i o n was c o n s i d e r e d t o be a minor problem, c o n f i n e d t o man made f i s h r e a r i n g f a c i l i t i e s . I t was o f t e n c a u sed by f a u l t y pumps and a i r e n t r a i n m e n t i n water i n t a k e p i p e s . A measure o f t h e degree o f s u p e r s a t u r a t i o n o f t h e water i s t h e t o t a l d i s s o l v e d gas p r e s s u r e CTGP), and i s e x p r e s s e d as a p e r c e n t o f s a t u r a t i o n . The water i s i n e q u i l i b r i u m w i t h t h e a i r a t 100% TGP. A t l e v e l s o f TGP above 100% t h e water i s s u p e r s a t u r a t e d w i t h gases. The degree o f s u p e r s a t u r a t i o n can a l s o be e x p r e s s e d as t h e e x c e s s d i s s o l v e d gas p r e s s u r e , AP. The two e x p r e s s i o n s a r e r e l a t e d by t h e e q u a t i o n : AP + BP TGP % = * 100 1.1 BP With t h e advent o f l a r g e s c a l e h y d r o — e l e c t r i c dams on th e Columbia and Snake R i v e r systems i n t h e 1960s, a s e r i o u s gas s u p e r s a t u r a t i o n problem d e v e l o p e d C E b e l , 1969). T o t a l gas p r e s s u r e CTGP) v a l u e s on t h e Columbia R i v e r were r e c o r d e d i n e x c e s s o f 130% o f s a t u r a t i o n C C l a r k , 1977). M a s s i v e k i l l s o f 2 m i g r a t i n g s a l m o n i d s a l e r t e d s c i e n t i s t s once a g a i n t o t h e problem. A r e l a t i o n s h i p was e s t a b l i s h e d between f i s h m o r t a l i t y and r e s e r v o i r s p i l l a g e o v e r h y d r o e l e c t r i c dams. D u r i n g f l o w p e r i o d s when water p a s s e d t h r o u g h t h e power g e n e r a t i n g t u r b i n e s and was not exposed t o t h e a e r a t i n g e f f e c t o f t h e s p i l l w a y s , s u p e r s a t u r a t i o n l e v e l s were low. D u r i n g t h e s p r i n g f l o o d p e r i o d , l e v e l s o f gas s u p e r s a t u r a t i o n were h i g h e s t . A t t h i s t i m e f l o w was r e l e a s e d o v e r s p i l l w a y s and a i r was e n t r a i n e d i n t h e water as i t p assed o v e r t h e dam. The i n c r e a s e d p r e s s s u r e as t h e water p l u n g e d i n t o t h e b a s i n below t h e dam f o r c e d a i r i n t o s o l u t i o n , and s u p e r s a t u r a t e d t h e water. These h i g h f l o w p e r i o d s c o r r e s p o n d e d t o t h e downstream m i g r a t i o n o f j u v e n i l e s a l m o n i d s , and r e s u l t e d i n a b n o r m a l l y h i g h m o r t a l i t i e s C B e i n i n g e n and E b e l , 1970). Water q u a l i t y c r i t e r i a f o r gas s u p e r s a t u r a t i o n were f o r m u l a t e d i n t h e USA. S i n c e f i s h were f o u n d t o be a f f e c t e d a t s u p e r s a t u r a t i o n l e v e l s o f 110% TGP o r g r e a t e r , t h e USEPA committee C1973) on water q u a l i t y c r i t e r i a e s t a b l i s h e d 110?; as t h e maximum a c c e p t a b l e l i m i t f o r TGP. However, t h e b i o l o g i c a l d a t a upon which t h e USEPA c r i t e r i a were based were t y p i c a l o f t h e Columbia R i v e r system and i t s h i g h l e v e l s o f gas s u p e r s a t u r a t e d water. The c r i t e r i a d i d n o t a c c o u n t f o r low l e v e l s o f TGP and t h e e f f e c t s o f l o n g term exposure. T h e r e f o r e , t h e c r i t e r i a may no t be a p p l i c a b l e t o t h e s e s i t u a t i o n s C C o l t , 1983). F o r example, f i s h h a t c h e r i e s a r e i n h e r e n t l y s u s c e p t a b l e t o low l e v e l s o f TGP CBouck, 1980). Stream m o d i f i c a t i o n s f o r j u v e n i l e r e a r i n g and t h e use o f ground water o f t e n r e s u l t i n s l i g h t l y . e l e v a t e d d i s s o l v e d gas p r e s s u r e s . R e a r i n g c h a n n e l s a r e s u b j e c t t o s o l a r h e a t i n g which d e c r e a s e s t h e gas s o l u b i l i t y o f t h e water. Ground water s u p p l i e s a r e o f t e n s u p e r s a t u r a t e d i n n i t r o g e n gas due t o t h e d e n i t r i f i c a t i o n o f n i t r a t e CSigma, 1983). S t u d i e s o f some s a l m o n i d h a t c h e r i e s have shown m o r t a l i t i e s t o o c c u r a t l e v e l s w e l l below 110% TGP. W r i g h t and McLean C1985) examined t h e e f f e c t s o f low l e v e l gas s u p e r s a t u r a t i o n on Chinook f r y i n a 122 day r e a r i n g p e r i o d . They a t t r i b u t e d a 2.5% m o r t a l i t y t o TGP l e v e l s a v e r a g i n g 105%. Growth was a l s o a f f e c t e d by TGP. The average w e i g h t o f f i s h h e l d i n a e r a t e d water CTGP = 100%) was s l i g h t l y more t h a n f i s h h e l d i n s u p e r s a t u r a t e d w a t e r, b u t t h i s was 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 . However, t h e c o n d i t i o n c o e f f i c i e n t s were s i g n i f i c a n t l y d i f f e r e n t , i n d i c a t i n g t h a t f i s h from a e r a t e d t r o u g h s were h e a v i e r r e l a t i v e t o t h e i r l e n g t h t h a n c o n t r o l f i s h ( W r i g h t and McLean, 1985). Dawley and E b e l C1975) r e p o r t e d t h a t e x p o s u r e o f j u v e n i l e Chinook and s t e e l h e a d t o 106% TGP f o r 35 days r e d u c e d growth r a t e s and i m p a i r e d swimming performance. M o r t a l i t y o f f i s h h e l d i n 106% TGP was n o t a t t r i b u t e d t o TGP s i n c e g r o s s symptoms o f GBT were n o t e v i d e n t . Bouck C1980) f o u n d t h a t h a t c h e r y t r o u t d i e d from GBT i n 105% TGP water. H a t c h e r y f i s h i n M i c h i g a n were a l s o d i s c o v e r e d t o be s e n s i t i v e t o low l e v e l s o f TGP. Westers C1983) r e p o r t e d g r e a t e r t h a n 70% m o r t a l i t y f o r brown t r o u t CSal mo t r u i t a ) and f o r rainbow t r o u t CSalmo gairdneri') a t t o t a l gas p r e s s u r e s l e s s t h a n 108%. The l i t e r a t u r e 4 c l e a r l y i n d i c a t e s t h a t m o r t a l i t y from GBT can o c c u r below t h e USEPA c r i t e r i u m o f 110%. A t t h e s e l o w e r l e v e l s o f TGP no e v i d e n c e o f v a s c u l a r system b u b b l e s have been r e p o r t e d . However, o t h e r symptoms o f GBT a r e e v i d e n t . The symptoms o f t e n t a k e t h e form o f o v e r e x p a n s i o n o f t h e swimbladder, i n t e s t i n a l t r a c t and a c c u m u l a t i o n o f gases i n t h e b u c c a l c a v i t y . D e t e r m i n a t i o n o f a t h r e s h o l d l e v e l o f TGP t h a t w i l l i n d u c e GBT i s v i t a l l y i m p o r t a n t f o r t h e p r o t e c t i o n o f m i g r a t i n g s a l m o n i d s t o c k s and r e a r i n g o f j u v e n i l e s a l m o n i d s i n h a t c h e r i e s . D e t e c t i o n o f t h e l o w e s t l e v e l o f TGP t h a t w i l l i n d u c e growth o f b u b b l e s c o u l d i n d i c a t e s a f e l e v e l s o f TGP. To f i n d a t h r e s h o l d f o r e m b o l i growth, F i d l e r C1984) examined t h e p h y s i c a l p arameters a f f e c t i n g t h e f o r m a t i o n o f b u b b l e s i n t h e v a s c u l a r system, swimbladder and t h e ambient water. H i s work i n d i c a t e s t h a t m o r t a l i t i e s can o c c u r a t TGP l e v e l s below t h e t h r e s h o l d f o r bub b l e f o r m a t i o n i n t h e v a s c u l a r system. A l d e r d i c e and Je n s e n C1985) have a l s o s u g g e s t e d m o r t a l i t y r e s p o n s e s a r e d i v i d e d i n t o two c a t e g o r i e s , a c u t e and c h r o n i c . A c u te m o r t a l i t y i s l i k e l y t o r e s u l t from i n t r a v a s c u l a r b u b b l e growth when TGP l e v e l s exceed 110%. C h r o n i c m o r t a l i t y i s p r o b a b l y a r e s u l t o f e x t r a v a s c u l a r b u b b l e growth. The h o l l o w o r g a n s C i e . g a s t r o - i n t e s t i n a l t r a c t , b u c c a l c a v i t y and swimbladder) a r e a r e a s t h a t show an a c c u m u l a t i o n o f gases when f i s h a r e exposed t o gas s u p e r s a t u r a t e d water. Jensen C1980) a s s o c i a t e d m o r t a l i t y i n s t e e l h e a d a l e v i n s w i t h b u b b l e s i n t h e b u c c a l c a v i t y . C o r n a c h i a and C o l t C1984) o b s e r v e d b u b b l e s i n t h e d i g e s t i v e t r a c t o f l a r v a l s t r i p e d b ass 5 (Morone saxatilis'), t h a t produced damage t o t h e e p i t h e l i a l c e l l s . H y p e r i n f l a t i o n o f t h e swimbladder has a l s o been o b s e r v e d C S h i r a t a , 1966; C o r n a c h i a and C o l t , 1984; J.O.T. J e n s e n , P a c i f i c B i o l o g i c a l S t a t i o n , Nanaimo, B.C., p e r s o n a l communication). T h i s s t u d y f o c u s e s on o v e r i n f l a t i o n o f t h e swimbladder, i t s e f f e c t s on t h e f i s h , and t h e r e s p o n s e o f t h e f i s h t o t h e e x c e s s buoyancy. The downloading o f b l o o d gases i n t o t h e swimbladder i s dependent on t h e degree o f v a s c u l a r i z a t i o n o f t h e c a v i t y w a l l . P h y s o c l i s t s have w e l l v a s c u l a r i z e d s w i m b l a d d e r s , p o s s e s s i n g gas s e c r e t i o n and gas r e a b s o r p t i o n s u r f a c e s . These s t r u c t u r e s a l l o w d ownloading o f oxygen from a r t e r i a l b l o o d t o t h e b l a d d e r a s a means o f m a i n t a i n i n g buoyancy a t depth. Gas s u p e r s a t u r a t i o n o f water has been c o n c l u d e d t o cause p o s i t i v e buoyancy i n t h e p h y s o c l i s t A t l a n t i c C r o a k e r CMicropogon undulatus) CChamberlain et al., 1980). U n l i k e t h e A t l a n t i c C r o a k e r , s a l m o n i d s a r e physostomes and l a c k s p e c i a l i z e d gas t r a n s f e r o r g a n s , and a r e n o t a b l e t o a d j u s t b l a d d e r volume by gas s e c r e t i o n and r e a b s o r p t i o n CSteen, 1970). Physostomes p o s s e s s a s h o r t d u c t t h a t c o n n e c t s t h e swimbladder t o t h e esophagus, known as t h e pneumatic d u c t . Gas needed t o i n f l a t e t h e swimbladder i s f o r c e d i n v i a t h e pneumatic d u c t by g u l p i n g a i r a t t h e s u r f a c e CFange, 1976). The swimbladder w a l l i s v a s c u l a r i z e d p r i m a r i l y by a r t e r i e s from t h e c o e l i a c a r t e r y C J a s i n s k i , 1963). These b l o o d v e s s e l s a r e p r o b a b l y s u f f i c i e n t t o a l l o w t h e passage o f gases from t h e 6 a r t e r i a l system a c r o s s t h e swimbladder w a l l , w hich may cause t h e swimbladder t o h y p e r i n f l a t e . S t r o u d et al. C1975) r e p o r t e d t h a t j u v e n i l e s a l m o n i d s u s u a l l y e x h i b i t e d d i s t e n d e d s wimbladders a f t e r e x p o s ure t o e x c e s s TGP. c o n t r a s t t o t h e v a s c u l a r system, t h e p r e s s u r e r e q u i r e d t o overcome t h e s u r f a c e t e n s i o n f o r c e s t h a t r e s t r i c t b u b b l e growth i s low. C o n s e q u e n t l y , i f a r t e r i a l b l o o d o f t h e f i s h i s i n e q u i l i b r i u m w i t h t h e ambient water gas t e n s i o n s , swimbladder i n f l a t i o n s h o u l d o c c u r whenever t h e TGP exceeds a t m o s p h e r i c p r e s s u r e . However, t h e r a t i o o f P(>2 i n t h e a r t e r i a l system t o P 0 2 i n t h e water CF r a t i o ) i s l e s s t h a n one due t o t h e d i f f u s i o n r e s i s t a n c e a t t h e g i l l and consumption o f oxygen a t t h e t i s s u e s . C o n s e q u e n t l y , t h e t o t a l d i s s o l v e d gas p r e s s u r e i s l o w e r i n t h e a r t e r i a l system t h a n i n t h e ambient water and TGP l e v e l s g r e a t e r t h a n 100% a r e r e q u i r e d f o r downloading o f gas i n t o t h e swimbladder. F i d l e r C1985) t o o k t h e s e p a r a m e t e r s i n t o a c c o u n t and d e r i v e d a r e l a t i o n s h i p f o r t h e t h r e s h o l d TGP t h a t w i l l cause swimbladder o v e r i n f l a t i o n . F o r a f i s h h e l d i n gas s u p e r s a t u r a t e d water, t h e t h r e s h o l d e q u a t i o n i s : The swimbladder i s an organ t h a t can be c o n s i d e r e d t o be a v e r y l a r g e bubble. As s u c h t h e r a d i u s i s v e r y l a r g e . I n TGP S B - B 1.2 where: B C 7 T G P _ = BP + AP S B P(>2 = p a r t i a l p r e s s u r e o f oxygen i n t h e water BP = b a r o m e t r i c p r e s s u r e F = r a t i o o f a r t e r i a l PC>2 t o water PC>2 p = t h e d e n s i t y o f water h = t h e depth o f water K = H N ° N /H D / o o H N = H e n r y s c o n s t a n t f o r n i t r o g e n H Q = H e n r y s c o n s t a n t f o r oxygen D N = D i f f u s i v i t y o f n i t r o g e n D Q = D i f f u s i v i t y o f oxygen F o r d e r i v a t i o n o f t h i s e q u a t i o n s e e F i d l e r C1985). F i d l e r C1984) s u g g e s t e d t h a t m o r t a l i t y a t TGP l e v e l s l e s s t h a n 110% must be a s s o c i a t e d w i t h o v e r i n f l a t i o n o f t h e h o l l o w organs. D i r e c t m o r t a l i t y has been o b s e r v e d from r u p t u r e o f s w i m b l a d d e r s i n rainbow t r o u t h e l d i n gas s u p e r s a t u r a t e d water C S h i r a t a , 1966). T h i s r e s u l t i m p l i e s t h a t t h e p r e s s u r e f o r v e n t i n g o f gas o u t t h e pneumatic d u c t was g r e a t e r t h a n t h a t t o b u r s t t h e swimbladder membrane. T h e r e f o r e , t h e p r e s s u r e f o r r e l e a s e o f gas t h r o u g h t h e pneumatic d u c t must be examined. One o f t h e few r e s e a r c h e r s t o d e t e r m i n e t h e pneumatic d u c t r e l e a s e p r e s s u r e CDRP) on physostomes was Harvey C1963). He d e t e r m i n e d DRP f o r soc k e y e s m o l t s t o be 28 mmHg. A p r e s s u r e o f t h i s magnitude does n o t seem adequate t o damage t h e swimbladder membrane, b u t i t may d i f f e r f o r d i f f e r e n t s p e c i e s and d i f f e r e n t s i z e s o f f i s h . The physostome pneumatic d u c t i s h i g h l y c o n v o l u t e d and v a r i e s i n d i a m e t e r a l o n g i t s l e n g t h . F i d l e r C1984) s u g g e s t e d t h a t t h e r e l e a s e p r e s s u r e i s a s s o c i a t e d w i t h t h e 8 minimum r a d i u s o f t h e pneumatic d u c t and s u r f a c e t e n s i o n f o r c e s . The r e l e a s e p r e s s u r e w i l l be r e l a t e d t o t h e r a d i u s o f t h e pneumatic d u c t and can be d e s c r i b e d by t h e L a p l a c e E q u a t i o n . 2 a Pi - Po = 1.3 r Where Pi. i s t h e b u b b l e i n t e r n a l p r e s s u r e Po i s t h e e x t e r n a l p r e s s u r e a i s t h e s u r f a c e t e n s i o n r i s t h e b u b b l e r a d i u s From e q u a t i o n 1.3, t h e DRP w i l l be i n v e r s e l y r e l a t e d t o t h e d u c t r a d i u s . The minimum p r e s s u r e t o overcome t h e s u r f a c e t e n s i o n f o r c e s and a l l o w gas t o move a l o n g t h e d u c t i s d e t e r m i n e d by t h e s m a l l e s t r a d i u s . I f t h e r a d i u s i s r e l a t e d t o t h e s i z e o f t h e f i s h , t h e d u c t r e l e a s e p r e s s u r e w i l l be l a r g e r f o r s m a l l f i s h . An i n c r e a s e i n swimbladder p r e s s u r e from g a s e s d i f f u s i n g i n t o t h e swimbladder w i l l a l s o r e s u l t i n a volume i n c r e a s e i n t h e f i s h due t o e x p a n s i o n o f t h e swimbladder. I n c r e a s e s i n t h e volume o f t h e f i s h w i l l r e s u l t i n a d e c r e a s e i n t h e d e n s i t y o f t h e f i s h , making i t p o s i t i v e l y buoyant. T h e r e f o r e , e v a l u a t i o n o f t h e p r e s s u r e / v o l u m e r e l a t i o n s h i p f o r t h e swimbladder i s i m p o r t a n t . I f a s i z e r e l a t i o n s h i p e x i s t s f o r t h e DRP, t h e buoyant l i f t e x e r t e d on t h e f i s h by swimbladder o v e r i n f l a t i o n may a l s o be s i z e r e l a t e d . F i s h may seek d e p t h t o compensate f o r an o v e r i n f l a t e d swimbladder. The i n c r e a s e d h y d r o s t a t i c p r e s s u r e w i l l compress t h e swimbladder and a l l e v i a t e p o s i t i v e buoyancy. However, d e p t h compensation has n o t been shown c o n c l u s i v e l y CWeitkamp and K a t z , 9 1980). Shrimpton C1985) showed that juvenile coho salmon COncorhynchus kisutch^ d i s t r i b u t e d themselves deeper with increasing TGP. However, f i s h l e s s than 8g were used, and a depth compensation response may be dependent on si z e . I examined t h i s response to determine what impact o v e r i n f l a t i o n of the swimbladder would have on the depth d i s t r i b u t i o n of salmonids. Whether f i s h seek depth to compensate f o r gas supersaturated water or not, most f i s h culture f a c i l i t i e s do not provide the depth required f o r f i s h to a l l e v i a t e GBT. In such a s i t u a t i o n f i s h may have to swim continuously to overcome the l i f t caused by swimbladder o v e r i n f l a t i o n . I f f i s h are unable to swim continuously, they may be c a r r i e d to the surface where they become more susceptable to predation. Many observations i n the l i t e r a t u r e indicate that swimbladder o v e r i n f l a t i o n i s a symptom of GBT, and i s a serious problem f o r young salmonids. Since there have been few measurements to define the response of the swimbladder to elevated TGP, I have set out to demonstrate the physiological changes associated with the swimbladder due to dissolved gas supersaturation of water. Using Rainbow trout CSalmo gairdneri} as the experimental animals i n t h i s study, a number of re l a t i o n s h i p s were determined on a range of f i s h s i z e s . These re l a t i o n s h i p s included: 1. The threshold TGP that w i l l cause swimbladder i n f l a t i o n ; 2 . The swimbladder i n t e r n a l pressure that w i l l cause venting of gas v i a the pneumatic duct CDRP)j 3 . The change i n f i s h density r e s u l t i n g from swimbladder o v e r i n f l a t i o n ; 4. Alterations i n behaviour that suggest water depth i s used by the f i s h to compensate f o r changes i n body density. 11 2.0 METHODS AND MATERIALS 2.1 PRODUCTION OF SUPERSATURATION AND WATER ANALYSIS The water TGP was controlled precisely using two aerator systems. One, designed to supersaturate the water, was constructed out of four inch PVC pipe, f i l l e d with 3/4 inch p l a s t i c i n t e r l o c saddles and sealed at both ends. Water and compressed a i r Cor oxygen) were introduced into the top of the column and allowed to pass through the substrate under pressure. Adjustment of a i r and water flow rates determined the dissolved gas pressure. Pressure f l u c t u a t i o n s i n the water system were controlled by an i n l i n e water flow regulator which maintained a constant water pressure and therefore, a constant t o t a l gas pressure CTGP). Water at the University of B r i t i s h Columbia i s naturally supersaturated Capproximately 104%). As I was interested i n the response of the swimbladder at dissolved gas pressures near equilibrium, gas had to be removed from solution by aerating the water at a pressure below atmospheric. The st r i p p i n g column was constructed out of four inch ABS pipe, f i l l e d with 3/4 inch Koch f l e x i r i n g s , sealed at the top, with the bottom of the pipe r e s t i n g i n a 15 L p a i l . Water was introduced into the top and passed through the column under a s l i g h t vacuum. The vacuum was created by a water aspirator connected to the top of the column. Outflows from both aerators ran into a mixing chamber. 12 Desired TGP l e v e l s could be achieved by adjusting mixture r a t i o s . Vater from the mixing chamber was gravity fed into the f i s h holding f a c i l i t i e s . The dissolved gas pressure d i f f e r e n t i a l CAP) was measured using a Novatech Designs model 300 C tensionometer. From AP and the barometric pressure CBP), the Total Gas Pressure CTGP) could be calculated from equation 1.1. The tensionometer probe was continuously agitated by a B u r r e l l Wrist Action Shaker to prevent a i r bubbles forming on the tubing membrane which would prevent the passage of gases into the membrane. The p a r t i a l pressure of oxygen C P O 2 ) was measured using a Radiometer oxygen electrode and meter Cmodule PHA 930). The oxygen meter was cal i b r a t e d d a i l y with a i r equili b r a t e d water and oxygen stripped water. Water temperature was measured using a mercury thermometer with 0.1 °C gradations. Barometric pressure was measured using a wall mounted mercury F o r t i n barometer. The dissolved gas oxygen:nitrogen r a t i o CONR) was calculated from these measurements by d i v i d i n g the percent 0 2 saturation by the percent N 2 saturation. The percent saturation of oxygen was calculated by: %0 2 = P0 2 / 0.2094 CBP - PH 20) 2.1 The percent saturation of nitrogen was calculated by: %N 2 = CBP + AP - P0 2 - PH 20) / 0.7902 CBP - PH 20) 2.2 N 2 includes Argon. 2-2 DETERMINATION OF SWIMBADDER INFLATION THRESHOLD The threshold TGP required f o r i n f l a t i o n of the swimbladder was detected by measuring the increase i n swimbladder pressure of f i s h held i n gas supersaturated water. Measurement of swimbladder pressure was accomplished by cannulating the swimbladder. Fish were anaesthetized i n 1:10,000 Tricaine methanesulphonate CMS-222) and placed on t h e i r side i n a c l o t h hammock. Water containing 1:15,000 MS-222 was perfused over the g i l l s by a r e c i r c u l a t i n g pump i n normal d i r e c t i o n of water flow. A hole was made i n the side of the f i s h approximately 0.5 cm below the l a t e r a l l i n e and mid-way along the length of the f i s h with a No. 20 s u r g i c a l needle. An 8 cm length of t e f l o n tubing CO.56 x 0.25 mm ID x WALL) with a r i g h t angle bend 1.5 cm from one end was guided into the swimbladder with a s t e e l guitar wire. The cannula was secured i n place with sutures through the adjacent muscle CFigure 1). Forcing a i r into the swimbladder u n t i l bubbles were expelled out the mouth ensured correct positioning of the cannula. Also, the f i s h were dissected a f t e r each experiment to v e r i f y placement of the cannula. An 80 cm long piece of gas impermeable nylon tubing connected the cannula to a Statham P23 BB pressure transducer. A suture of cotton thread was passed through the snout and used to hold the f i s h to a cross piece at the front of a clear p l e x i g l a s s r e s t r a i n i n g box open at both ends. The f i s h and the r e s t r a i n i n g box were then placed into a darkened box with a depth of 8 cm. The f i s h was revived by perfusing the g i l l s with fresh 14 Figure 1. Diagram of apparatus used i n the measurement of swimbladder pressure f o r f i s h held i n a i r supersaturated *rater. The f i s h was restrained i n the box by a suture through the nose that anchored i t to a crosspiece on the box and denied i t access to the surface. water. The f i s h were allowed to acclimate with the ambient water before data a q u i s i t i o n began. The swimbladder pressure, dissolved gas pressure d i f f e r e n t i a l and the oxygen p a r t i a l pressure were monitored every 100 seconds by a Data Translation Data Aqu i s i t i o n system controlled by a personal computer. Data was stored on floppy disks f o r l a t e r analysis. 2.3 DETERMINATION OF PNEUMATIC DUCT RELEASE PRESSURE In supersaturated water swimbladder pressure increased, making the f i s h p o s i t i v e l y buoyant. The pressure continued to r i s e u n t i l i t exceeded a threshold f o r venting of gas out the pneumatic duct. This pressure, the pneumatic duct release pressure CDRP) determined the extent of buoyancy the f i s h would experience. To determine the pressure that could be maintained within the swimbladder before venting of gas, two methods were used. The f i r s t method measured swimbladder pressure d i r e c t l y . The second method involved reducing environmental pressure u n t i l gas was expelled from the swimbladder, and c a l c u l a t i o n of duct release pressure. 2.3.1 Direct Measurement of Pneumatic Duct Release Pressure To measure swimbladder pressure d i r e c t l y , the cannula inserted into the swimbladder was connected to a pressure transducer CStatham P23 BB), as described i n section 2.2. Duct release pressure was determined by i n j e c t i n g a i r into the swimbladder at 0.625 ml/min. Measurements of swimbladder pressure and time were taken every second using the data a q u i s i t i o n system. Successive r i s e s i n pressure were followed by rapid drops i n swimbladder pressure corresponding to swimbladder venting v i a the pneumatic duct. A i r i n j e c t i o n had several advantages i n that i t was e a s i l y repeated and could be performed on a f i s h i n concert with the experiments to determine the threshold f o r swimbladder i n f l a t i o n i n gas supersaturated water. However, accuracy i n cannulating small f i s h was d i f f i c u l t , therefore t h i s method was r e s t r i c t e d to f i s h greater than 30 g. 2.3.2 Indirect Measurement of Pneumatic Duct Release Pressure A modification of Harvey's C1963) method f o r duct release pressure was used f o r f i s h weighing l e s s than 50 g. This method required measurement of the swimbladder volume and then determination of duct release pressure. A small chamber was constructed with a f i n e l y graduated pipette to detect volume changes i n the f i s h as the pressure was altered CFigure 2). An anaesthetized f i s h was placed inside the apparatus. I n i t i a l l y the pressure was increased by increments of 50 kP C380 mmHg) up to 150 kP. The change i n volume of the f i s h from the increased pressure was due to swimbladder compression. Since the gases within the swimbladder must conform to Boyle's Law, the volume of the swimbladder at atmospheric pressure CV^) can be calculated i f the change i n volume CdV), the barometric pressure a R d the chamber pressure CP 7) are known. The relationship: 1 7 VACUUM GAUGE Figure 2. Apparatus used to measure the pressure within the swimbladder required to force gas out through the pneumatic duct f o r f i s h l e s s than SOg. 18 P l V l = P2 V2 2 ' 3 w i l l apply. The volume of gas i n the swimbladder under pressure can then be described by: V 2 = V ± - dV 2.4 Solving equations 2.3 and 2.4 f o r gives: P 2 * dV V. = 2.5 P2 " P l = swimbladder volume at atmospheric pressure V 2 = swimbladder volume at increased pressure dV = change i n swimbladder volume = barometric pressure P 2 = chamber pressure Determination of the DRP was accomplished by decreasing the chamber pressure below atmospheric pressure. As the swimbladder expands the swimbladder wall and the f i s h musculature r e s t r i c t further expansion. Consequently the swimbladder pressure i s higher than the chamber pressure and gas i s expelled out the pneumatic duct. Pressure was decreased i n the chamber u n t i l bubbles of a i r were released from the swimbladder, at which time the chamber pressure and change i n volume were recorded. The swimbladder pressure was calculated by: P l * V l Po = 2.6 V V3 P3 = swimbladder pressure V3 = VI + dV 20 pressure increase can be calculated from the t o t a l volume of the f i s h . Determination of volume i s tedious and inaccurate. However, the volume of the f i s h can be calculated i f i t s density i s known. The density of f i s h with deflated swimbladder i s the most constant value and tends to deviate l i t t l e . Harvey C1963) found sockeye smolts to average 1.0634 g/ml, with l i t t l e variance. Although Harvey'S determinations were made over a lim i t e d s i z e range, the value may be a reasonable approximation of the rainbow trout density with swimbladder deflated. The density of the f i s h at DRP can be determined i f the weight, volume of the swimbladder at DRP and density of the f i s h with no swimbladder are known. The mass divided by 1.0634 plus the volume of swimbladder at DRP w i l l equal the t o t a l volume of the f i s h . V F = V S B + [ M F 1 2 8  F SB L 1.0634 J The density i s then mass divided by volume. D = — — 2.9 V p = Total volume of the f i s h V* „ = Volume of the swimbladder S B rT = Mass of the f i s h F D = Density of the f i s h at DRP The density of the f i s h can also be expressed as a l i f t f actor, which i s the r a t i o of the environmental water density <Pe> to the f i s h density Cp f). This value i s the inverse of Lowdes C1942) sinking factor. 21 2.10 When t h i s r a t i o i s greater than 1, the f i s h w i l l be p o s i t i v e l y buoyant. The magnitude of the buoyant l i f t i s d i r e c t l y proportional to LF. 2.5 BEHAVIOURAL EXPERIMENTS Changes i n the swimbladder volume due to gas supersaturation cause a change i n the buoyancy of the f i s h . Examination of f i s h behaviour may reveal i f the f i s h compensate f o r t h i s decrease i n density. This was accomplished by monitoring the v e r t i c a l movements of f i s h . Testing depth change as a function of t o t a l gas pressure was conducted on rainbow trout ranging i n s i z e from 2 to 50 g. An observation column C200x47x50 cm HxWxDD constructed from 3/4 inch plywood with a ple x i g l a s s f r o n t was used to observe depth d i s t r i b u t i o n changes i n the t e s t f i s h at d i f f e r e n t l e v e l s of TGP CFigure 3). Markings on the side of the observation column indicated f i s h depth. Water of known TGP was introduced into the observation column f o r each t r i a l . A s i n g l e f i s h was placed i n the column and allowed time to acclimate to the water conditions and become accustomed to the column. Only one f i s h was used per t r i a l to avoid group behavioral interactions that may have resulted i n f i s h not holding at the preferred depth. The f i s h was then observed i n the column with a video camera over an 8 hour period C1600 to 2400 Hr). The depth of the f i s h i n the water was determined to 19 The pneumatic duct release pressure (DRP) was equal to the difference between the swimbladder pressure and the chamber pressure at DRP (P2). DRP P3 - P2 2.7 The apparatus was ca l i b r a t e d regularly over the range of po s i t i v e and negative pressures studied and in d i v i d u a l values f o r a f i s h were corrected f o r d i s t o r t i o n of the apparatus. 2.4 SWIMBLADDER EXPANSION Determination of the change i n density of a f i s h due to swimbladder o v e r i n f l a t i o n i s accomplished by measuring the increase i n volume of the swimbladder and the f i s h . Expansion of the swimbladder due to an increase i n bladder pressure was measured i n the same apparatus used to determine the duct release pressure f o r small f i s h . The volume of the swimbladder was determined as described f o r i n d i r e c t measurement of pneumatic duct release pressure CSection 2.3.2). After measurements f o r the c a l c u l a t i o n of swimbladder volume were taken, the chamber pressure was decreased and changes i n swimbladder volume recorded f o r every 10 kP (75 mmHg) reduction i n pressure from one atmosphere u n t i l bubbles were expelled from the mouth of the f i s h . In practice the experiments were c a r r i e d out simultaneously with the duct release pressure work. The change i n density of the f i s h due to swimbladder 22 totflm I DEPTH 5ML: METERS -I L2 Figure 3 . Diagram of the observation column used to monitor the depth d i s t r i b u t i o n of rainbow trout f o r d i f f e r e n t l e v e l s of TGP. Total depth of the water was 2 meters. Water flowed into the column at a rate of S L/min. 23 the nearest 10 cm at approximately 3 minute in t e r v a l s . The mean depth and standard deviation were determined from the i n d i v i d u a l observations. A d i f f e r e n t l e v e l of supersaturated water was then introduced into the column, and the f i s h given time to acclimate Capproximately 24 hours). Depth f o r the f i s h was again monitored with the video. Each f i s h was observed at two or more l e v e l s of TGP ranging from 100% CAP = 0) to 120% CAP = ISO). Afterwards the f i s h was removed from the column, weighed to within O.lg and body length measured to within 1mm. 24 3.0 RESULTS 3.1 RESPONSE OF SWIMBLADDER TO GAS SUPERSATURATED WATER Fish exposed to gas supersaturated water show an increase i n swimbladder pressure. I f the water TGP i s high enough, the swimbladder pressure w i l l continue to r i s e u n t i l i t exceeds a l e v e l that w i l l force gas out through the pneumatic duct. Figure 4 i s a t y p i c a l example of swimbladder pressure increase f o r a f i s h held i n supersaturated water of 106.6% TGP CAP = SO mmHg). Pressure within the swimbladder rose to 14.1 mmHg. At t h i s pressure, gas was forced out the pneumatic duct. The sudden drop i n pressure i s c h a r a c t e r i s t i c of swimbladder gas venting, which can also be seen i n Figure 5 where multiple duct releases were created by infusing a i r into the swimbladder at a constant rate. A i r infused into the bladder caused an increase i n pressure, u n t i l a l e v e l was reached that could force open the pneumatic duct. The s i m i l a r i t y between the pressures required to release gas out the pneumatic duct during a r t i f i c i a l i n f l a t i o n and d i f f u s i o n of supersaturated gases into the swimbladder can be seen i n Figures 4 and 3. After the venting of gas CFigure 4), the continued d i f f u s i o n of supersaturated gases into the swimbladder of the f i s h should have resulted i n a further increase i n swimbladder pressure. However, upon examination of the cannula, drops of water could be seen occluding the tubing and preventing further measurement of swimbladder pressure. This 23 S W I M B L A D D E R P R E S S U R E V S T I M E 15-10-1986 195g FISH 0 2 4 6 8 TIME hours Figure 4. Increase i n swimbladder pressure f o r a l°5g rainbow •trout, held i n gas supersaturated water CAP = 50 mmHg ± 2). The rapid drop i n pressure a f t e r 5 hours i s associated with venting of gas out the pneumatic duct. 26 Figure S . Venting of gas out the pneumatic duct when a i r was infused into the swimbladder at a rate of 0.625 ml/min. The sharp drops i n pressure are c h a r a c t e r i s t i c of gas release from the swimbladder. 27 pattern was seen often and may r e s u l t from the sudden drop i n pressure asssociated with venting of gases. Detection of a TGP threshold f o r swimbladder i n f l a t i o n proved d i f f i c u l t due to the long response time associated with swimbladder i n f l a t i o n . Often the cannula became occluded with water, and changes i n bladder pressure were impossible to detect. Figure 6 shows a response f o r a f i s h held i n water near the threshold f o r swimbladder i n f l a t i o n . More than IS hours were required f o r the pressure i n the swimbladder to exceed the DRP. The i n i t i a l response of the swimbladder showed no consistent trend, as the pressure o s c i l l a t e d between 1 and 5 mmHg. As the d i f f u s i o n of gases into the swimbladder i s expected to be slow at these l e v e l s of TGP, the changes i n pressure detected by the pressure transducer are most l i k e l y due to moisture i n the cannula preventing free movement of a i r . Sudden changes i n swimbladder pressure caused by struggling movements and contraction of s k e l e t a l muscle CMcGutheon, 1966) may be s u f f i c i e n t to dislodge a water drop from occluding the cannula. For example, the sudden r i s e i n swimbladder pressure at s i x hours i s i n d i c a t i v e of water occluding the cannula (Figure 6). Beyond t h i s time period the bladder pressure increased u n t i l i t reached a l e v e l at 16 hours where gas was expelled out the pneumatic duct. Figure 7 i s the a r t i f i c i a l l y induced duct release pressures f o r the same f i s h . After each duct release, the decrease i n swimbladder pressure i s small. Consequently, the f i s h w i l l continuously have an excess i n swimbladder pressure and 28 SWIMBLADDER PRESSURE VS TIME 22-09-1986 184g FISH TIME hours Figure 6. Increase i n swimbladder pressure f o r a 184g rainbow trout held i n gas supersaturated water CAP = 29 mmHg ± 2). The uneven increase i n pressure over the f i r s t 8 hours i s l i k e l y due to moisture i n the cannula. PNEUMATIC DUCT RELEASE PRESSURE 23-09-1986 184g FISH TIME seconds Figure 7 . Release of gas out the pneumatic duct during infusion of a i r into the swimbladder of a 184g rainbow trout. Infusion of a i r began at 30 seconds and ended at 220 seconds. 30 be p o s i t i v e l y buoyant,. The minimum AP found to cause an increase i n swimbladder pressure was 27 mmHg. Gas tensions below t h i s resulted i n a reduction of swimbladder pressure and a loss of gas. This was confirmed when f i s h were dissected to determine placement of the cannula within the swimbladder. During dissec t i o n i t was easy to see the r e l a t i v e i n f l a t i o n of the swimbladder. Commonly, f i s h held i n supersaturated water above the threshold had large extended swimbladders. However, at t o t a l gas pressures l e s s than 27 mmHg, the swimbladders were obviously underinflated. As there was no opportunity f o r the f i s h held i n the boxes to reach the surface, these animals could not i n f l a t e t h e i r swimbladders by swallowing a i r . When these f i s h were held i n water near equilibrium or below, they slowly l o s t gas from the swimbladder. The d i f f u s i o n gradient determines the rate of swimbladder pressure increase and i s a function of the t o t a l gas pressure. The i n f l a t i o n rate can be calculated from the r i s e i n swimbladder pressure over time. P l o t t i n g the i n f l a t i o n rate CdP/dt; the slope of the increase i n swimbladder pressure) against the dissolved gas pressure d i f f e r e n t i a l CAP) resulted i n 2 a l i n e a r r e l a t i o n s h i p CR = 0.966) when the ONR Coxygen:nitrogen r a t i o ) i s constant at 0.95 CFigure 8). As the TGP increases the rate of d i f f u s i o n into the swimbladder from the a r t e r i a l system must also increase. I t can also be seen that the swimbladder w i l l loose pressure when TGP i s below equilibrium or below the 31 1.8 H 1.6 1.4 -1.2 -1 -0.8 0.6 H 0.4 0.2 -0 --0.2 --0.4 --0.6 --0.8 --1 + + SWIMBLADDER INFLATION RATE AS A FUNCTION OF TGP "~T~ 20 40 60 80 DISSOLVED GAS PRESSURE mmHg Figure 8. Rate of increase i n swimbladder pressure (mmHg per hour) f o r rainbow trout held i n d i f f e r e n t l e v e l s of gas supersaturated water. The ONR was constant f o r a l l the data points, at 0.95. 32 threshold f o r d i f f u s i o n of gases into the bladder CAP < 27 mmHg for an ONR of approximately 1.0). The threshold f o r swimbladder i n f l a t i o n i s also dependent on the P0 2 of the water. I t was not possible to maintain a constant P0 2 over a wide range of TGP; consequently the P0 2 tended to increase with the TGP throughout the experiments, keeping the ONR r e l a t i v e l y constant. To examine the e f f e c t that changing the ONR would have on swimbladder i n f l a t i o n , the water was supersaturated with oxygen, which resulted i n oxygen p a r t i a l pressures i n excess of 250 mmHg and nitrogen p a r t i a l pressures s l i g h t l y below equilibrium. At higher l e v e l s of P0 2, the threshold TGP f o r hyperinflation of the swimbladder increased. For example, at a P0 2 of 250 mmHg the threshold AP that caused an increase i n bladder pressure was greater than 40 mmHg. Although the va r i a t i o n i n the ONR altered the threshold f o r d i f f u s i o n of gas into the swimbladder, i t did not s i g n i f i c a n t l y a f f e c t the rate of i n f l a t i o n . Choosing data points with the same P0 2, showed that an increase i n AP resulted i n a corresponding increase i n i n f l a t i o n rate. Five s e r i e s of data points were used. Each s e r i e s had s i m i l a r l e v e l s of P0 2. Linear regression of dP/dt on AP with P0 2 was calculated f o r the f i v e d i f f e r e n t oxygen l e v e l s CTable 1). Analysis of covariance showed no s i g n i f i c a n t difference between the regression c o e f f i c i e n t s CF = 1.0305, P > 0.50). Changing the ONR of the water r e s u l t s i n a seri e s of equations describing dP/dt against AP that are a l l 33 x P0 2 ± s. e. n b mmHg mmHg/Hr 152.2 0. 462 15 0.0589 158.9 0.773 8 0.0404 168.9 0.455 7 0.0462 274. 9 2.641 7 0.0383 322. 2 1.237 9 0.0484 common 0.0480 Table 1. S t a t i s t i c s f o r regression of rate of swimbladder i n f l a t i o n on dissolved gas tension f o r f i v e l e v e l s of PO2* ^ the PO2 could not be kept constant over the whole range of t o t a l gas pressures tested, only those data points were chosen that had si m i l a r P0 2. The standard error term expresses the deviation i n PO2 of these data points. The c o e f f i c i e n t calculated by l i n e a r regression i s b. 34 p a r a l l e l , but o f f s e t from one another depending on the P0 2. Multiple l i n e a r regression performed on the swimbladder i n f l a t i o n rate data showed a s i g n i f i c a n t i n t e r r e l a t i o n s h i p of the independent variables CAP, P0 2, Weight and Temperature) on the dependent variable, dP/dt. F f o r the regression was 87.42S CP 4 6 8 << 0.001). The p a r t i a l regression c o e f f i c i e n t s f o r AP CT = 18.136; P << 0.001) and P0 2 CT = -6.567; P < 0.001) indicated a s i g n i f i c a n t r e l a t i o n s h i p with dP/dt. Temperature was varied l i t t l e throughout each experiment C< 0.3°C), but ranged over the duration of the study from 8.0 to 16.3°G. However, i t was not found to s i g n i f i c a n t l y a f f e c t the rate of swimbladder i n f l a t i o n . The p a r t i a l regression c o e f f i c i e n t f o r temperature was 1.4507 CP > 0.1). Fish weight did not have a s i g n i f i c a n t e f f e c t on dP/dt. Trout ranged i n s i z e from 45 to 245g. The p a r t i a l regression c o e f f i c i e n t was -0.8605 CP > 0.2). When temperature and f i s h weight were excluded from regression analysis on the dP/dt data, the equation describing the r e l a t i o n s h i p between rate of swimbladder i n f l a t i o n on the dissolved gas tension and the p a r t i a l pressure of oxygen was: dP/dt = 0.04142 CAP) - 0.007316 CP0 2) + 0.3634 3.1 F f o r the regression was 172.795 CP 2 7 Q « 0.001). R 2 = 0.832. Although, P0 2 determines the threshold f o r swimbladder i n f l a t i o n , AP determines the magnitude of the d i f f u s i o n gradient and consequently the rate of pressure buildup within the swimbladder. The data c o l l e c t e d on swimbladder i n f l a t i o n rate 35 (dP/dt) reveals that there i s a l e v e l of TGP that does not lead to an increase or decrease i n swimbladder pressure. This l e v e l of TGP i s the threshold f o r swimbladder o v e r i n f l a t i o n . Comparison of the data from t h i s study and the threshold equation 1.2 ( F i d l e r , 1985) i s presented i n Figure 9. TGP l e v e l s above the threshold l i n e lead to swimbladder o v e r i n f l a t i o n , whereas those below the threshold l i n e lead to bladder d e f l a t i o n . The dP/dt data points are denoted p o s i t i v e f o r increases i n swimbladder pressure and negative f o r decreases i n swimbladder pressure. Clearly data c o l l e c t e d i n t h i s study support the v a l i d i t y of F i d l e r ' S C1985) threshold equation. 3.2 PNEUMATIC DUCT RELEASE PRESSURE The threshold pressure that w i l l force a i r through the pneumatic duct i s dependent on the s i z e of the f i s h CFigure 10). Small f i s h have higher duct release pressures than large f i s h . Within the s i z e group 1 - 10 g there i s a steep increase i n DRP as f i s h become smaller. There i s l e s s difference i n DRP among f i s h larger than approximately 30 g; although i t i s s t i l l evident that larger f i s h have lower duct release pressures. This was seen f o r a r t i f i c i a l l y induced DRP from infusing a i r into the swimbladder and release pressures observed f o r f i s h held i n supersaturated water. A logarithmic transformation of the data forms a s t r a i g h t l i n e (Figure 11). Linear regression on the transformed 36 0> I E E t Ui I 0. P 140 130 120 110 H 100 90 -f 80 - j 70 - i 60 - j 50 -j 40-j i 30 H 20 -| 10 -j 140 SWIMBLADDER OVERINFLATION DATA TGP VS WATER P02 + + + + + + + % 1 SWIMBLADDER ~ OVERINFLATION THRESHOLD + + + + ++ ™ i — r 160 ~ T ~ T 180 ~ " i — r — r ~ 200 220 i — i — v — i i — i — r — r — r 240 260 280 300 T " 320 340 WATER P02 mmHg Figure 9. Plot- of -the t o t a l gas pressure threshold equation derived by F i d l e r C19855 as a function of the water PO2. Data from t h i s study i s also plotted. + indicates dP/dt was p o s i t i v e and the swimbladder i n f l a t e d - indicates dP/dt was negative and the swimbladder deflated 37 X E E & D OT bi cc a. 1 a d Q DUCT RELEASE PRESSURE VS WEIGHT 30 -IX 20 -10 H # + + FOR RAINBOW TROUT + . + + + + + + 0 4 0 ~7 T 1 1 1 1 T i 1 1 r 40 BO 120 160 200 FISH WEIGHT g + Method 1 X Method 2 1 240 Figure 10. The r e l a t i o n s h i p between the in t e r n a l swimbladder pressure required to force gas out the pneumatic duct and the weight of the f i s h f o r rainbow trout CSalmo gairdneri"). Method 1 r e f e r s to data points that were c o l l e c t e d by infusing a i r into the swimbladder at 0.623 ml/min. Method 2 r e f e r s to data points obtained using the method of Harvey C1963). 38 DUCT RELEASE PRESSURE VS WEIGHT FOR RAINBOW TROUT 1 2 3 5 10 20 30 50 100 200 300 FISH WEIGHT g + Method 1 X Method 2 Figure 11. A plot, of the logarithmically transformed data showing the r e l a t i o n s h i p between the pneumatic duct release pressure and the weight of the f i s h . Method 1 and method 2 ref e r to methods described on Figure 10. 39 data gave the equation: DRP = Vt " ° - 2 8 8 * 60 3.2 R 2 f o r the equation 0.842. The DRP shows a response related to the minimum radius of the pneumatic duct as described by the Laplace equation f o r surface tension. The pneumatic duct radius that corresponds to the DRP can be calculated by equating the DRP equation with the Laplace equation. DRP P - P 3.3 V t " 0 - 2 8 8 * 60 = -2-2_ 3.4 Solving the equation f o r r C^ nm) and using a surface tension of 74.22 dynes/cm, gives: r = V t 0 * 2 8 8 * 18.6 3.S During experiments to determine the pneumatic duct release pressure using Harveys C1963) method, several f i s h were not observed to release gas out the mouth. In each case the f i s h became grossly corpulent from the swimbladder gases expanding u n t i l bubbles of a i r were observed to escape from the anus. Presumably the swimbladder of these i n d i v i d u a l s had ruptured, preventing escape of gas out the pneumatic duct. In each of these cases the f i s h weighed le s s than 10 g. 3.3 SVIMBLADDER EXPANSION The volume of the swimbladder i s related to the 40 pressure within the swimbladder. At low swimbladder pressures, further increases i n pressure lead to r e l a t i v e l y large increases i n volume. This can be seen i n Figure 12 as the f l a t part of the curve. Thus, the most rapid change i n volume w i l l occur before a large buildup i n pressure has occurred. At higher pressures the change i n volume i s reduced, as swimbladder expansion i s r e s t r i c t e d by the membrane and surrounding body tissues. The bladder pressure i s only a l l e v i a t e d by release of gas out the pneumatic duct. Figure 12 shows the pressure/volume r e l a t i o n s h i p f o r a 9.5 g rainbow trout. I t can be seen that the volume of the swimbladder more than doubles before the duct release pressure i s reached. Although the doubling of the volume gives an in d i c a t i o n of the density change of the f i s h , i t i s dependent on the i n i t i a l volume of the swimbladder, which may be underinflated or overinflated. Thus, the maximum volume change must be determined i n r e l a t i o n to the t o t a l volume of the f i s h . P l o t t i n g the calculated density at the duct release pressure reveals that small f i s h w i l l experience the largest change i n density from neutral buoyancy CFigure 13). Regression analysis on the log transformed data resulted i n the equation: DENS = 0.931 * VT 0 0 1 7 3.6 R 2 f o r the equation i s 0.725. The exponential r e l a t i o n s h i p of the data indicates that small f i s h w i l l have a tremendous buoyancy change before gas i s expelled out the pneumatic duct. The f l a t t e n i n g of the curve 41 VOLUME CHANGE WITH INCREASED PRESSURE 40 FOR A 9.5g RAINBOW TROUT I E E 35 30 - t t DC Ui o o 25 -i 2 20 H o Ui a V) (0 Ul a a. 15 10 5-4 0.4 "~T~ 0.6 I 0.8 0.2 VOLUME OF SWIMBLADDER ml Figure 12. The re l a t i o n s h i p between the int e r n a l pressure and the volume of the swimbladder f o r a 9.5g rainbow trout. 42 Figure 13. Density of rainbow trout at the threshold pressure f o r venting of gas through the pneumatic duct as a function of the f i s h weight. 43 above 20 g i n weight s i g n i f i e s a smaller change i n buoyancy f o r t h i s s i z e range of f i s h . Figure 14 shows the l i f t f a c t o r experienced by a f i s h when the swimbladder pressure equals the DRP. 3.4 BEHAVIOURAL RESPONSE The mean depth of f i s h i s dependent on the t o t a l gas pressure and the s i z e of the f i s h . Small f i s h , l e s s than 10 grams compensate f o r increasing TGP by seeking greater depth. Larger f i s h show a depth d i s t r i b u t i o n that appears independent of the TGP. Many f i s h spent long periods of time swimming up and down the column. This was c l e a r l y evident at TGP near equilibrium. Consequently the mean depth was near the centre of the column C100 cm depth). Increasing the TGP did not have a constant e f f e c t on f i s h above 40 g; some were higher i n the column, some lower and some did not change t h e i r mean depth. However, f i s h below 10 g i n weight exhibited a deeper depth f o r increasing TGP. Although many of these f i s h would s t i l l swim up and down the length of the column, the r e l a t i v e frequency of f i s h i n the top sections of the water column decreased with increased t o t a l gas pressure. Multiple regression on mean depth as a function of AP and weight resulted i n a non-linear response. F f o r the regression was 5.098 CP R < 0.01), and R 2 was 0.338. The non-linear r e s u l t was due to several f i s h holding near the bottom of the column at a l l t o t a l gas pressures tested. As t h i s i s most 44 Figure 14. The l i f t f a c t o r calculated f o r a swimbladder pressure at the DRP as a function of the f i s h weight. 45 l i k e l y a behaviour that i s independent of the t o t a l gas pressure, the data was normalized by comparing the change i n depth to the weight and AP. A multiple l i n e a r regression on the data resulted i n the highest value of Fj F was 18.106 CP., _„ < 0.001) and R 2 was 0.521. The gross mean depth f o r a l l s i z e s of f i s h i n equilibr a t e d water was then calculated and added to the constant i n the equation. The mean depth Ccm) i s described by: Depth = 0.532CAP) - 0.0419CVt) -0.0137CAP*Vt) + 110.1 3.7 A comparison of the depth d i s t r i b u t i o n equation to the compensation depth f o r swimbladder o v e r i n f l a t i o n i s shown i n Figure 15. Hydrostatic pressure w i l l maintain supersaturated gases i n solution. The compensation depth i s where the hydrostatic pressure reduces the excess dissolved gas pressure to the threshold f o r swimbladder i n f l a t i o n CAPU = 27 mmHg). As the TGP increases, the depth required to maintain the dissolved gases i n s o l u t i o n also increases. I t can be seen that large f i s h spend more time above the compensation depth at high l e v e l s of AP than small f i s h . Although the model indicates that large f i s h do not experience swimbladder o v e r i n f l a t i o n , many behaviour patterns i n d i c a t i n g p o s i t i v e buoyancy were observed during the study. At a AP of 116 mmHg a 50 g f i s h held p o s i t i o n i n the top corner of the observation column f o r long periods of time. The t a i l and dorsal f i n of the f i s h broke the surface as i t held p o s i t i o n with the head down and the t a i l slowly o s c i l l a t i n g . At a AP of 80 Figure IS. Depth d i s t r i b u t i o n f o r rainbow trout CSalmo gairdneri^ as a function of the dissolved gas pressure d i f f e r e n t i a l CAP) and the weight of the f i s h . The compensation depth required to a l l e v i a t e d i f f u s i o n of gas into the swimbladder i s also plotted CAP U = 27mmHg). 47 mmHg a 35 g f i s h was observed to hold position i n the water column at a depth of 40 cm with the head down and t a i l beating. This body posture i s i n d i c a t i v e of f i s h that are p o s i t i v e l y buoyant. Large f i s h appear to be p o s i t i v e l y buoyant i n supersaturated water, but do not compensate f o r the buoyancy problem by seeking greater depth. The magnitude of the buoyant l i f t i s small and i t plays no r o l e i n determining the depth d i s t r i b u t i o n of the f i s h . 48 4.0 DISCUSSION When exposed to water supersaturated with atmospheric gases, rainbow trout e x h i b i t an increase i n the in t e r n a l pressure of the swimbladder. The threshold f o r gas d i f f u s i o n into the swimbladder e x i s t s at a AP of 27 mmHg when the water P0 2 i s 160 mmHg. Increasing the proportion of oxygen i n the water w i l l increase the threshold. Therefore, a higher AP i s required f o r di f f u s i o n of gases into the swimbladder as the P0 2 increases. In hyperoxic water CP0 2 = 250 mmHg) the threshold AP f o r swimbladder i n f l a t i o n i s approximately 45 mmHg. Although TGP i s the p r i n c i p a l component determining dP/dt, the constituent gases dissolved i n the water also have an ef f e c t on the rate of i n f l a t i o n of the swimbladder. The di f f u s i o n c o e f f i c i e n t f o r oxygen i s greater than that f o r nitrogen CKrogh, 1919). An increase i n the ONR should r e s u l t i n an increase i n dP/dt. However, t h i s i s a small factor and the a r t e r i a l P0 2 has greater bearing on the rate of i n f l a t i o n . This i s due to the lower l e v e l of P0 2 i n the a r t e r i a l system i n r e l a t i o n to the water, and i s expressed as the F r a t i o . The r a t i o i s always le s s than one CRandall and Daxboeck, 1984). Diffusi o n resistance at the g i l l s and the consumption of oxygen at the tissues prevents the 0 2 l e v e l i n the f i s h tissues from f u l l y e q u i l i b r a t i n g with the water, unlike nitrogen. Consequently the a r t e r i a l PO^ i s lower than the water P0^ and the 49 threshold f o r blood gases to d i f f u s e into the swimbladder i s not at 100% TGP. The F r a t i o w i l l also vary with the ambient water P0 2 and a l t e r the threshold. During hyperoxia the g i l l water flow i s reduced CRandall and Daxboeck, 1984), and the oxygen gradient between water and blood increases. Equation 1.2 CFidler, 198S) predicts a threshold TGP f o r swimbladder o v e r i n f l a t i o n , and the data from t h i s work agrees well with F i d l e r ' s prediction. The convergence of the data points onto a l i n e indicates the existance of a threshold. The equation shows a strong e f f e c t of P0 2 on the threshold; f o r an increase i n P0 2 the threshold AP f o r swimbladder o v e r i n f l a t i o n w i l l also increase. The d i f f u s i o n of gases through the tissues i s influenced by the ambient temperature. Increasing temperature r a i s e s the d i f f u s i o n c o e f f i c i e n t CVelty e t . a l . , 1984). In t h i s study, the multiple l i n e a r regression analysis showed the p a r t i a l regression c o e f f i c i e n t was positive. The standard error around the c o e f f i c i e n t was r e l a t i v e l y large, and the c o e f f i c i e n t was not s i g n i f i c a n t . The p o s i t i v e p a r t i a l regression c o e f f i c i e n t indicates that r i s e s i n temperature increase the rate of swimbladder o v e r i n f l a t i o n . The rate of swimbladder i n f l a t i o n i s also affected by f i s h s i z e . The lower surface area to volume r a t i o of the bladder i n large f i s h causes a slower increase i n pressure. I f the d i f f u s i o n gradient remains constant, the rate of increase i n volume w i l l be dependent on the surface area to volume r a t i o of 50 the bladder. The large surface area to volume r a t i o , corresponding to the swimbladder of a small f i s h , w i l l expand more ra p i d l y than the swimbladder of a large f i s h . Over the s i z e range of f i s h used i n t h i s study, a cle a r r e l a t i o n s h i p was never established. However, the f i s h were a l l greater than 40g and the e f f e c t of the surface area to volume r a t i o may only become discernable at much smaller s i z e s when the r a t i o becomes much greater. Although accumulation of gas i n the swimbladder of salmonids has been shown by several researchers CWittenberg, 1958; Fahlen, 1971; Sundes et. a l . , 1958), i t has never been attributed to gas supersaturation. They had proposed that salmonids a c t i v e l y secrete gas into the swimbladder. However, the l i n e a r r e l a t i o n s h i p of dP/dt with AP indicates that blood gases d i f f u s e down a concentration gradient into the swimbladder when rainbow trout are held i n supersaturated water. The tissu e layers of the swimbladder are arranged such that the main d i f f u s i o n b a r r i e r to gases i s exterior to the blood supply CLapennas and Schmidt-Nielsen, 1977; Morris and Albright, 1979). Consequently, gas exchange i s not r e s t r i c t e d between the vascular system and the swimbladder. However, movement of gas into the swimbladder i s slow. The structure of the salmonid swimbladder also suggests that movement of gas must be by d i f f u s i o n . The component layers of the membrane are simple. The simple vascular arrangement w i l l allow d i f f u s i o n , but i s not complex enough to produce secretion 31 of gas into the trout bladder CJasinski, 1963). The i n a b i l i t y of trout and salmon to secrete gas into the swimbladder i s further demonstrated by Harvey C1963) and T a i t C1956). They found eit h e r no change i n swimbladder volume or a decrease i n swimbladder volume i n experiments where f i s h were prevented from reaching the water surface. Harvey C1963) also found that sockeye held i n water with low oxgen tension (2 ppm) showed a rapid reduction i n the swimbladder oxygen content. Presumably, the oxygen diffused out of the swimbladder to a region of lower oxygen tension. C o n f l i c t i n g r e s u l t s i n the l i t e r a t u r e on the r e l a t i v e i n f l a t i o n of the swimbladder during s i m i l a r experimental conditions may be explained by TGP. I t i s l i k e l y the differences i n supersaturation of the water supplies used by the researchers that has lead to differences i n res u l t s . D i f f u s i o n of supersaturated blood gases into the swimbladder causes an increase i n pressure. The pressure w i l l r i s e u n t i l i t reaches a threshold f o r release of gas out the pneumatic duct. There i s a logarithmic r e l a t i o n s h i p between the f i s h s i z e and the pneumatic duct release pressure. The very high DRP values f o r f i s h l e s s than lOg, indicate that a considerable pressure buildup w i l l occur within the swimbladder before gas i s vented. I t has been postulated that DRP i s controlled by a sphincter muscle. However, Harvey C1963) found no obvious spincter present i n sockeye. The duct i s highly convoluted and F i d l e r C1984) suggested that the DRP may be a function of surface tension forces and the minimum radius of the pneumatic duct, and 52 •therefore conform to the Laplace Equation C1.3). Gas passage through the duct w i l l occur i f the gas pressure i n the swimbladder i s s u f f i c i e n t to overcome the surface tension forces of the duct. The radius of the pneumatic duct w i l l determine the minimum pressure required to overcome the surface tension forces and allow gas to move along the duct. Thus, the c r i t i c a l dimension of the duct i s the minimum diameter, which i s l i k e l y to change with the development of the f i s h . As the f i s h grows the radius of the pneumatic duct increases and duct release pressure decreases. I f f i s h are held i n supersaturated water, a small f i s h w i l l maintain a high pressure within the swimbladder; whereas a larger f i s h w i l l continuously vent gas and release swimbladder pressure. The Laplace Equation C1.3) can be used to cal c u l a t e the probable radius of the pneumatic duct. I t was found that the pneumatic duct radius c o n t r o l l i n g release of gas from the swimbladder was a function of weight raised to a power of 0.29. From the length and weight measurements on rainbow trout made i n t h i s study, the length was found to be related to weight raised to a power of 0.32. The s i m i l a r i t y i n the two exponents indicates that the radius of the pneumatic duct i s approximately proportional to the length of the f i s h . The release of gas out the pneumatic duct i s dependent on a d i f f e r e n t i a l pressure between the int e r n a l swimbladder pressure and the ambient water pressure. However, f r i g h t also causes the release of gas from the swimbladder of sockeye salmon 53 CHarvey, 1963). When s t a r t l e d f i s h dive and release a t r a i l of gas bubbles. The r e s u l t i s an increase i n f i s h density. In physostomes the smooth muscle of the swimbladder wall i s innervated by noradrenergic f i b e r s CFange, 1976; Fahlen et. al., 1965). Loss of gas induced by f r i g h t i s not a simple release of gas held under pressure i n the bladder. Instead, gas i s expelled f o r c i b l y from the swimbladder by contraction of the c i r c u l a r muscles of the swimbladder i n response to adrenalin, which causes a reduction i n the cross sectional area CBrawn, 1964; Harvey, 1963). Although salmonids have the a b i l i t y to vent swimbladder gas, i t i s a sympathetic response induced by f r i g h t . Consequently, o v e r i n f l a t i o n of the swimbladder due to supersaturated water appears not to induce the sympathetic response and the bladder does not release the excess pressure u n t i l the DRP i s reached. The swimbladder w i l l expand with an increase i n in t e r n a l pressure. The expansion of the swimbladder i s greatest at low pressures. At low swimbladder pressure the membrane and surrounding tiss u e tension i s low. As the volume continues to expand, further expansion i s r e s t r i c t e d by the reduced compliance of the adjacent tiss u e and musculature. The r e s t r i c t e d expansion leads to a large buildup i n pressure with a small change i n volume. The change i n volume, associated with the swimbladder pressure increase, causes an increase i n buoyancy. The r e l a t i o n -ship between pressure and volume of the swimbladder indicates 54 that the f i s h w i l l experience a buoyant force dependent on the degree of swimbladder o v e r i n f l a t i o n . The buoyant force w i l l be greatest when the swimbladder pressure approaches the duct release pressure. The f i s h used i n t h i s study experienced a buoyant force before swimbladder gas was vented. However, the e f f e c t i s s i z e related. Smaller f i s h experience the greatest l i f t . L i t e rature observations of abnormal p o s i t i v e buoyancy i n juvenile salmonids caused by gas supersaturated water substantiate these findings. Work on rainbow trout held i n supersaturated water at greater than 150% TGP showed a s i m i l a r response CShirata, 1966). Abnormal expansion of the swimbladder was one of the main symptoms of GBT a f t e r the f i s h were free swimming and had i n f l a t e d t h e i r swimbladders. Stroud et. al. C1975) found that p r i o r to death, juvenile salmonids held i n acutely l e t h a l l e v e l s of supersaturation, exhibited abnormal buoyancy. The f i s h were observed to f l o a t at the surface. Dissection of the f i s h revealed the swimbladder to be large and distended. Swimbladder o v e r i n f l a t i o n w i l l cause a buoyant force that must be compensated f o r by the f i s h . Either i t can continuously swim to o f f s e t the buoyancy or i t can swim to a greater depth where the hydrostatic pressure w i l l compress the swimbladder and obtain neutral buoyancy. Seeking depth w i l l be of benefit to the f i s h i n that the hydrostatic pressure also retains the supersaturated gas i n solut i o n CHarvey, 1975). The increased hydrostatic pressure has been shown to a l l e v i a t e S3 symptoms of GBT CVeitkamp and Katz, 1980). Caged steelhead exposed to a l e t h a l l e v e l of gas supersaturation at d i f f e r e n t depths, died most quickly i n shallow cages and most slowly i n deep cages CKnittel et. al., 1980). Depth provides protection against supersaturation by compensating f o r the excess dissolved gas pressure. Depth compensation f o r excess TGP i s a behaviour limi t e d to small f i s h ; f i s h below lOg showed a consistent increase i n depth with increases i n TGP. The response i s l i k e l y due to the high swimbladder pressures required f o r venting of the pneumatic duct. The high i n t e r n a l pressures lead to large changes i n density, f o r c i n g the f i s h to compensate f o r swimbladder o v e r i n f l a t i o n . To maintain neutral buoyancy the f i s h must seek depth to compress the swimbladder. Although large f i s h experience a smaller decrease i n density from swimbladder o v e r i n f l a t i o n , they are also l e s s affected by changes i n density. Harvey and Bothern C1972) showed that larger f i s h Cgreater than 20g) are capable of maintaining po s i t i o n over a wide range of pressures without a l t e r i n g behaviour. Sockeye showed no change i n behaviour f o r an increase i n pressure equal to 3 .5 m depth, but subsequent pressure increases e l i c i t e d a maximal response. However, changes i n behaviour of smaller sockeye were r e a d i l y apparent as soon as the pressure changed. Larger f i s h are stronger swimmers and are better able to compensate f o r changes i n density. Consequently they exh i b i t l e s s change i n depth when p o s i t i v e l y buoyant due to 56 gas supersaturation. These findings appear to be consistent with published data. A study on two year old rainbow trout C48-89g) showed that the mean swimming depth of f i s h held i n 117.3% TGP was not s i g n i f i c a n t l y d i f f e r e n t from f i s h i n equilibrium water CLund and Heggberget, 1985}. In f a c t , f i s h exposed to supersaturated water showed a tendency to swim at a shallower l e v e l than f i s h i n equilibrium water. Active depth compensation was i n s i g n i f i c a n t i n rainbow trout of t h i s s i z e . Movement to a greater depth i s a passive behaviour since the a b i l i t y to detect supersaturation by f i s h i s doubtful CVeitkamp and Katz,1980). In an avoidance experiment, steelhead did not demonstrate any s i g n i f i c a n t avoidance behaviour i n a choice trough study. Aggression between the f i s h caused considerable t e r r i t o r i a l a c t i v i t y which may have resulted i n the lack of avoidance (Stevens et. a l . , 1980). However, f i s h may respond to the symptoms of GBT and seek water where these symptoms do not p e r s i s t CD.F. Alderdice, P a c i f i c B i o l o g i c a l Station, Nanaimo, B.C., personal communication). Although f i s h may not detect and avoid supersaturation, several experiments have shown that i f depth i s available mortality i s greatly reduced. F i f t e e n gram Chinook allowed to seek depth i n a four meter cage did not s u f f e r m o r t a l i t i e s at saturations of up to 128% CVeitkamp, 1976). V i l d juvenile chinook with a mean weight of 19g, held i n water supersaturated at 130% i n a 9 m deep tank survived at a much higher rate than those i n shallow tanks CEbel et. a l . , 1971). Observations 57 indicated that most f i s h remained between about 1 and 4 m o f the s u r f a c e . V e r t i c a l d i s t r i b u t i o n o f 0.42g Chinook maintained a g r e a t e r depth at h i g h e r saturation l e v e l s than those at the lower l e v e l s CDawley et. a l . , 1976). I f depth i s not s u f f i c i e n t to f u l l y compensate f o r the dissolved gas supersaturation substantial m o r t a l i t i e s can occur CEbel and Raymond, 1976). A decrease i n f i s h density due to swimbladder o v e r i n f l a t i o n w i l l impose energetic constraints on the f i s h . P o s i t i v e buoyancy w i l l force f i s h to expend more energy i n swimming continuously to maintain position i n the water column, i f there i s inadequate hydrostatic pressure to allow f u l l compensation. Shallow ponds, well water systems and stream a l t e r a t i o n s may create supersaturation problems and do not allow f i s h any opportunity to compensate f o r the excess gas pressures. V i l d f i s h must cope with gas supersaturation associated with hydroelectric dams. Dissolved gas l e v e l s are subject to considerable seasonal f l u c t u a t i o n s and vary with the release of water over spillways of dams. On the Columbia River, TGP i s near equilibrium i n the f a l l and winter when no water i s s p i l l e d , and high (above 135%) i n spring and summer when large volumes of water are s p i l l e d . The downstream migration of juvenile salmonids coincides with the peak times f o r water s p i l l a g e over the dams CEbel, 1969). Young f i s h most s e n s i t i v e to swimbladder o v e r i n f l a t i o n often inhabit water with supersaturation l e v e l s l i k e l y to promote GBT. 58 5 .0 SUMMARY Rainbow trout held i n gas supersaturated water and denied access to the surface show an increase i n swimbladder pressure. The threshold dissolved gas pressure d i f f e r e n t i a l found to cause i n f l a t i o n of the swimbladder was 27 mmHg f o r an ONR of 0.95. Increase i n the ONR resulted i n a higher threshold AP f o r swimbladder i n f l a t i o n . Movement of gas into the swimbladder i s passive and w i l l cause a r i s e i n pressure u n t i l the d i f f u s i o n gradient i s n i l or the gas i s expelled out the pneumatic duct. The threshold f o r DRP i s related to the s i z e of the f i s h . Small f i s h have higher DRP values and are subject to the higher degree of pressure buildup within the swimbladder. Corresponding to the excess swimbladder pressure i s an expansion of swibladder volume. The volume change r e s u l t s i n a decrease i n density and postive buoyancy. Due to the high DRP of small f i s h , they experience the greatest decrease i n density. Once the DRP has been reached i n the swimbladder, a portion of the swimbladder gas i s released. The subsequent release of pressure does not a l l e v i a t e p o s i t i v e buoyancy completely. Therefore, a f i s h held i n supersaturated water w i l l continuously experience a buoyant force. The large change i n density causes small f i s h to increase depth and compensate f o r the swimbladder expansion. Although swimbladder i n f l a t i o n occurs f o r a l l s i z e s of trout held i n gas supersaturated water, the impact i s greatest f o r small f i s h . Therefore, f i s h that experience the greatest buoyant force must compensate by seeking depth. 60 6.0 LITERATURE CITED Alderdice, D.F. and J.O.T. Jensen. 1985. Assessment of the Influence of gas supersaturation on salmonids i n the Nechako River i n r e l a t i o n to Kemano completion. Canadian Technical Report of F i s h e r i e s and Aquatic Science No. 1386. Beiningen, K.T. and V.J. Ebel. 1970. E f f e c t of John Day Dam on dissolved nitrogen concentrations and salmon i n the Columbia River, 1968. Trans. Am. Fish. Soc. 99:664-671. Bouck, G.R. 1980. Etiology of gas bubble disease. Trans. Amer. Fish. Soc. 109:703-707. Brawn, V.M. 1964. Some functions of the swimbladder and i t s ducts i n A t l a n t i c and P a c i f i c herring. PhD. thesis, University of B r i t i s h Columbia. 256pp. Chamberlain, G.V. , V.H. N e i l l , P.A. Romanowsky and K. Strawn. 1980. V e r t i c a l responses of A t l a n t i c croaker to gas supersaturation and temperature change. Trans. Amer. Fish. Soc. 109:737-750. Clark, M.J.R. 1977. Environmental protection dissolved gas study: Data summary 1977. Province of B r i t i s h Columbia, Ministry of Environment, Report No. 77-10. Colt, J.E. 1983. The computation and reporting of dissolved gas le v e l s . Vater Res. 8:841-849. Cornachia, J.V. and J.E. Colt. 1984. The e f f e c t s of dissolved gas supersaturation on l a r v a l s t r i p e d bass, Morone s a x a t i l i s (Valbaum). J. Fish Diseases. 7:15-27. Dawley, E.M., M. Schiewe and B. Monk. 1976. E f f e c t s of long-term exposure to supersaturation of dissolved atmospheric gases on juvenile chinook salmon and steelhead trout i n deep and shallow t e s t tanks. p 1-10. In D.H. Fickiesen and M.J. Schneider Ceds), Gas Bubble Disease: Proceedings of a workshop held at Richland, Washington, October 8-9, 1974. Energy Res. Dev. Admin., Oak Ridge, Tennessee, USA. 61 Dawley, E.M., and V.J. Ebel. 1975. E f f e c t s of various concentrations of dissolved atmospheric gas on juvenile chinook salmon and steelhead trout. Fishery B u l l e t i n 73(4):787-796. Ebel, V.J. 1969. Supersaturation of nitrogen i n the Columbia r i v e r and i t s e f f e c t on salmon and steelhead trout. Fishery B u l l e t i n 68(1):1-11. Ebel, W.J. and H.L. Raymond. 1976. E f f e c t of atmospheric gas supersaturation on salmon and steelhead trout of the Snake and Columbia Rivers. Marine F i s h e r i e s Review 38(7):1-14. Ebel, V.J., E.M. Dawley and tolerance of juvenile P a c i f i c r e l a t i o n to supesaturation B u l l e t i n 69(4):833-843. B.H. Monk. 1971. Thermal salmon and steelhead trout i n of nitrogen gas. Fishery Fahlen, G. 1971. The functional morphology of the gas bladder of the genus Salmo. Acta Anat. 78:161-184. Fahlen, G., B. Falck and E. Rosengren. 1965. Monoamines i n the swimbladder of Gadus c a l l arias and Salmo i r i d e u s . Acta Physiol. Scand. 64:119-126. Fange, R. 1976. Gas exchange i n the swimbladder. p 189-211. In Respiration of amphibious vertebrates. Ed. G.M. Hughes. Academic Press, London. F i d l e r , L.E. 1985. A study of the biophysical phenoma associated with gas bubble trauma i n f i s h . MSc. Thesis, University of B r i t i s h Columbia 114pp. F i d l e r , L.E. 1984. A study of biophysical phenoma associated with gas bubble trauma i n fishes. Penny Applied Sciences, Ltd., Penny, B.C. 132pp. Harvey, H.H. 1975. Gas disease i n f i s h e s - a review. p 450 -485 In V. A. Adams (ed), Chemistry and Physics of Aqueous Gas Solutions. The Electrochemical Society, Princeton, New Jersey, USA. 62 Harvey, H.H. 1963. Pressure i n the early history of the Sockeye salmon. PhD thesis, University of B r i t i s h Columbia. 267pp. Harvey, H.H. and C.R. Bothern. 1972. Compensatory swimming i n the kokanee and sockeye salmon Oncorhynchus nerka CValbaum). J. Fish B i o l . 4:237-247. Ja s i n s k i , A. 1963. The vascularization of the a i r bladder i n fishes. Part I. A i r bladder of the bleak CCoregonus a l b u l a l and rainbow trout CSalmo i r i d e u s Gibb . 5 , and the ductus pneumaticus of the eel <.Angui.Ha a n g u i l l a L.). Acta Biologica Cracoviensia, Vol. VI:2-31. Jensen, J.O.T. 1980. E f f e c t of t o t a l gas pressure, temperature, and t o t a l water hardness on steelhead eggs and alevins In Northwest Fish Culture Conference. Courtney, B.C. K n i t t e l , M.D., G.A. Chapman and P.R. Garton. 1980. E f f e c t s of hydrostatic pressure on steelhead s u r v i v a l i n air-supersaturated water. Trans. Amer. Fish. Soc. 109:7SS-759. Krogh, A. 1919. The rate of d i f f u s i o n of gases through animal tissues, with some remarks on the c o e f f i c i e n t of invasion. J. Physiology 52:391-408. Lapennas and Schmidt-Nielsen. 1977. Swimbladder permeability to oxygen. J. Exp. Biology 67:175-196. Lowndes, A.G. 1942. The displacement method of weighing l i v i n g aquatic organisms. J. Mar. B i o l . Assoc. UK. 25:555-574. Lund, M. and T.G. Heggberget. 1985. Avoidance response of two—year old rainbow trout, Salmo gairdneri Richardson, to a i r supersaturated water: hydrostatic compensation. J. Fish B i o l . 26:193-200. Marsh, M.C. and F.P. Gorham. 1905. The gas disease i n fishes. Report of the United States Bureau of Fisheries. C1904):343-376. McCutcheon, F.H. 1966. Pressure s e n s i t i v i t y , reflexes, and buoyancy responses i n teleosts. Animal Behav. 14:204-217. 63 Morris, S.M. and J.T. Albright. 1979. Ultrastructure of the swim bladder of the g o l d f i s h , Carassius aurat us. C e l l and Tissue Res. 198:105-117. Pauley, G. B. and R.E. Nakatani. 1967. Histopathology of "gas bubble" disease i n salmon f i n g e r l i n g s . J. Fish. Res. Bd. Canada 24:867-871. Randall, D.J. and C. Daxboeck. 1984. Oxygen and carbon dioxide transfer across f i s h g i l l s pp 263-314 In V.S. Hoar and D.J. Randall Ceds), Fish Physiology, Vol. 10A. Academic Press, New York, USA. Shirata, S. 1966. Experiments on nitrogen gas disease with rainbow trout f r y . B u l l e t i n of Freshwater F i s h e r i e s Research Laboratory CTokyo). 15C2>:197-211. Shrimpton, J.M. 1985. Response of coho salmon COncorhynchus kisutchy to d i f f e r e n t l e v e l s of gas supersaturation. BSc Thesis, University of V i c t o r i a , B r i t i s h Columbia. 44pp. Sigma Resource Consultants Ltd. 1983. Water q u a l i t y c r i t e r i a f o r salmonid hatcheries. Report to Department of F i s h e r i e s and Oceans, Vancouver, B.C. Steen, J.B. 1970. The swimbladder as a hydrostatic organ, p 413-443. In W.S. Hoar and D.J. Randall Ceds), Fish Physiology, Vol. 4. Academic Press, New York, USA. Stevens, D.G., A.V. Nebeker and R.J. Baker. 1980. Avoidance responses of salmon and trout to air—supersaturated water. Trans. Amer. Fish. Soc. 109:751-754. Stroud, R.K., G.R. Bouck and A.V. Nebeker. 1975. Pathology of acute and chronic exposure of salmonid f i s h e s to supersaturated water. p 435—449 In W.A. Adams Ced) Chemistry and Physics of Aqueous Gas Solutions. The Electrochemical Society, Princeton, New Jersey, USA. Sundnes, G., T. Enns and P.F. Scholander. 1958. Gas secretion i n f i s h e s lacking rete mirabile. J. Exp. Biology 35C3):671-676. 64 T a i l , J.S. 1936. Nitrogen and argon i n salmonoid swimbladders. Can. J. Zool. 34:38-62. USEPA. 1973. Quality c r i t e r i a f o r water. Washington, D i s t r i c t of Columbia, USA. Weitkamp, D.E. 1976. Dissolved gas supersaturation: Live cage bioassay at Rock Island Dam, Washington. In D.H. Fickeisen and M.J. Schneider Ceds), Gas Bubble Disease: Proceedings of a workshop held at Richland, Washington, October 8-9, 1974, p 24-36. Energy Res. Dev. Admin., Oak Ridge, Tennessee, USA. Weitkamp, D.E. and M. Katz. 1980. A review of dissolved gas supersaturation l i t e r a t u r e . Trans. Amer. Fish. Soc. 109:659-702. Welty, J.R., C.E. Wicks and R.E. Wilson. 1984. Fundamentals of momentum, heat, and mass transfer. 3rd edi t i o n . Wiley, New York, USA 803pp. Westers, H. 1983. Experience i n Michigan with gas supei— saturation. In Gas Supersaturation Conference, Milwaukee, Wisconsin, USA. Wittenberg, J.B. 1958. The secretion of i n e r t gas into the swimbladder of f i s h . J. Gen. Physiol. 41C4):783-804. Wright, P.B. and W.E. McLean. 1984. The e f f e c t s of aeration on the rearing of summer Chinook f r y COncorhynchus tshauytschcD at the Puntledge Hatchery. Dept. Fish. Oceans, Vancouver, B.C. 47pp. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0097852/manifest

Comment

Related Items