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Daily rings in otoliths of sockeye salmon (Oncorhynchus nerka) and their relationship to growth 1981

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DAILY RINGS IN OTOLITHS OF SOCKEYE SALMON ( O n c o r h y n c h u s n e r k a ) AND THEIR R E L A T I O N S H I P TO GROWTH b y K e n n e t h H. W i l s o n B . S c , 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 , 1977 A T H E S I S SUBMITTED IN P A R T I A L F U L F I L L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H COLUMBIA M a r c h 1981 (c) K e n n e t h H. W i l s o n MASTER OF S C I E N C E i n t h e D e p a r t m e n t o f Z o o l o g y I n 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 l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree 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 a g r e e t h a t t h e 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 agree 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 h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s . I 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 n o t 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 . Department o f 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 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date i i ABSTRACT This study reports the occurrence of d a i l y r i n g s i n the o t o l i t h s of Oncorhynchus nerka f r y and examines t h e i r r e l a t i o n s h i p to growth. In experiment 1, sockeye salmon f r y were c o l l e c t e d from the Fulton River spawning channel a t Babine Lake, B r i t i s h Columbia i n May 1978. The f i s h were reared f o r 26 days i n enclosures i n the spawning channel and were sampled every seven to ten days. S a g i t t a e were removed from 25 f i s h from each sample, and the growth r i n g s i n one o t o l i t h from each f i s h were counted. A re g r e s s i o n o f the number of r i n g s on the number of days since capture showed t h a t these r i n g s a r e , on average, formed d a i l y , beginning at the time of emergence. A number of p o s s i b l e t e c h n i c a l and b i o l o g i c a l causes o f v a r i a t i o n i n r i n g counts w i t h i n and between samples are considered. In Experiment 2, sockeye salmon f r y were reared i n the la b o r a t o r y from f e r t i l i z e d eggs taken i n the f a l l of 1978 at the Weaver Creek spawning channel near M i s s i o n , B r i t i s h Columbia. A random sample of 64 of these f r y was marked to enable i d e n t i f i c a t i o n of i n d i v i d u a l s . Each i n d i v i d u a l was weighed i n i t i a l l y on June 6 or 8, again on J u l y 6, and s u r v i v i n g f i s h were weighed a t h i r d time on J u l y 20. A f t e r a f i n a l weighing, s a g i t t a e were removed and a standard o t o l i t h radius was deter- mined by counting back the appropriate number of d a i l y r i n g s which c o r r e s - ponded to each weight. The re g r e s s i o n of £n o t o l i t h radius on £n f i s h weight was l i n e a r , and had an R 2 of 0.92, which demonstrates a r e l a t i o n - ship between the mean width o f a d a i l y r i n g i n sockeye salmon f r y s a g i t t a e , and a mean d a i l y change i n the weight of the f r y . Using t h i s r e g r e s s i o n l i n e , we bac k - c a l c u l a t e d the previous weight of the i n d i v i d u a l f i s h from i i i the corresponding o t o l i t h radius and a l a t t e r f i s h weight and o t o l i t h radius and found the e r r o r s to be r e l a t i v e l y small — i n the order of 15 per cent. i v TABLE OF CONTENTS Page TITLE PAGE . 1 ABSTRACT i i TABLE OF CONTENTS i v LIST OF FIGURES v i LIST OF TABLES v i i LIST OF APPENDICES v i i i ACKNOWLEDGEMENTS i x INTRODUCTION 1 GENERAL METHODS 9 F i s h P r e s e r v a t i o n 9 O t o l i t h Removal 9 O t o l i t h S t o r a g e 11 O t o l i t h P r e p a r a t i o n and O b s e r v a t i o n 11 EXPERIMENT 1: DAILY GROWTH RINGS IN THE OTOLITHS OF JUVENILE SOCKEYE SALMON (Oncorhynchus nerka) 15 I n t r o d u c t i o n 15 Methods 16 R e s u l t s IV D i s c u s s i o n 19 EXPERIMENT 2: THE RELATIONSHIP BETWEEN WIDTuH OF DAILY GROWTH RINGS IN SAGITTAE AND CHANGE IN BODY SIZE OF SOCKEYE SALMON (Oncorhynchus nerka) 23 I n t r o d u c t i o n 23 Methods 23 V R e s u l t s 30 D i s c u s s i o n 36 SUMMARY 42 LITERATURE CITED 43 APPENDIX 1 The back c a l c u l a t i o n of p r e v i o u s f i s h w e i g h t from c o r r e s p o n d i n g p r e v i o u s o t o l i t h r a d i u s and a l a t t e r o t o l i t h r a d i u s and f i s h w e i g h t . . 45 APPENDIX 2 Annotated photographs of O. nerk a o t o l i t h s as an a i d to age and growth a n a l y s i s 48 v i LIST OF FIGURES Page F i g u r e 1. The l a b y r i n t h o f the cod, Gadus morhua (L.) showing the r e l a t i o n s h i p between the semi- c i r c u l a r c a n a l s and the o t o l i t h chambers 2 F i g u r e 2. S a g i t t a e of 0. n e r k a f r y 3 F i g u r e 3. Appearance of 0. n e r k a f r y b e f o r e and a f t e r removal of lower jaw, g i l l c o v e r s and g i l l s t o r e v e a l s a g i t t a e 10 F i g u r e 4. S a g i t t a e from a 0. n e r k a f r y removed from the e n c l o s u r e on June 9 18 F i g u r e 5. Graph of o t o l i t h r i n g count v e r s u s age i n days s i n c e emergence 20 F i g u r e 6. S a g i t t a e of an 0. n e r k a f r y removed from the e n c l o s u r e on May 13 22 F i g u r e 7. C o l d b r a n d i n g s i t e s i n an 0. n e r k a f r y 25 F i g u r e 8. S a g i t t a e of an 0. n e r k a f r y showing r o s t r u m , p o s t - r o s t r u m , n u c l e i and l o c a t i o n o f p r e f e r r e d r a d i u s 27 F i g u r e 9. S a g i t t a e of 0. n e r k a f r y removed from tank on J u l y 2 29 F i g u r e 10. £n f i s h weight v e r s u s in o t o l i t h r a d i u s f o r i n d i v i d u a l f i s h (No's 1-29) at the i n i t i a l (June 6 o r 8 ) , second ( J u l y 6) and, where a p p l i c a b l e , t h i r d ( J u l y 20) w e i g h i n g 31 F i g u r e 11. P l o t o f r e s i d u a l s from l i n e a r r e g r e s s i o n of f i s h weight on £n o t o l i t h r a d i u s as shown i n F i g u r e 10 32 F i g u r e 12. S a g i t t a e of O. n e r k a f r y showing p o s s i b l e t y p e s of back c a l c u l a t i o n of p r e v i o u s f i s h w e i g h t u s i n g the c o r r e s p o n d i n g p r e v i o u s o t o l i t h r a d i u s and a l a t t e r f i s h weight and o t o l i t h r a d i u s as d e s c r i b e d i n the t e x t . . . . 35 F i g u r e 13. R e s i d u a l s o f back c a l c u l a t e d weight {Un back c a l c u l a t e d f i s h weight - Zn observed f i s h w e i g h t ) v e r s u s p r e d i c t e d Jin weight 37 LIST OF TABLES Page Ta b l e I an o t o l i t h r a d i u s ( AnR) and in f i s h weight (JlnW) f o r e x p e r i m e n t a l f r y at the i n i t i a l (June 6 o r 8 ) , second ( J u l y 6 ) , and t h i r d ( J u l y 20) w e i g h i n g s 33 vi i i LIST OF APPENDICES Appendix 1 The back c a l c u l a t i o n of p r e v i o u s f i s h w e i g h t from c o r r e s p o n d i n g p r e v i o u s o t o l i t h r a d i u s and a l a t t e r o t o l i t h r a d i u s and f i s h w e i g h t 45 Appendix 2 Annotated photographs of 0. n e r k a o t o l i t h s as an a i d to age and growth a n a l y s i s 48 i x ACKNOWLEDGEMENTS I am d e e p l y g r a t e f u l t o Dr. P. A. L a r k i n f o r h i s g u i d a n c e , encouragement and s u p p o r t . I a l s o wish to thank Helen Hahn, G a i l Sugden, M o i r a Greaven, B i l l Gazey, John N e i l s o n , Cameron West and many o t h e r s f o r t h e i r h e l p and a d v i c e , and g r a t e f u l l y acknowledge f i n a n c i a l s u p p o r t p r o v i d e d by the Marine Resources Branch, M i n i s t r y o f Environment of the Government of B r i t i s h Columbia and the N a t u r a l S c i e n c e s and E n g i n e e r i n g Research C o u n c i l of Canada. I a l s o thank the Department o f F i s h e r i e s and Oceans, Canada, the s t a f f o f the F u l t o n R i v e r spawning c h a n n e l , and the I n t e r n a t i o n a l P a c i f i c Salmon f i s h e r i e s commission f o r t h e i r c o o p e r a t i o n . 1 INTRODUCTION The o t o l i t h s o f t e l e o s t f i s h e s are p a r t s of the l a b y r i n t h system. The t y p i c a l t e l e o s t f i s h has s i x o t o l i t h s , t h r e e i n each l a b y r i n t h ; a s a g i t t a i n each s a c c u l u s , an a s t e r i s c u s i n each l a g e n a , and a l a p i l l u s i n each u t r i c u l u s . The s a g i t t a i s almost i n v a r i a b l y the l a r g e s t o t o l i t h i n n o n - o s t e r i o p h y s i d s . F i g u r e 1 ( a f t e r B l a c k e r 1974) shows the l a b y r i n t h of a cod (Gadus morhua) and the a s s o c i a t e d o t o l i t h s . F i g u r e 2 ( a f t e r T aubert and Coble 1977) r e p r e s e n t s the s a g i t t a of a sockeye salmon (Oncorhyncus n e r k a ) . Each o t o l i t h i s composed p r i m a r i l y (85-90 p e r cent) of argo- n i t e ( c a l c i u m c a r b o n a t e ) , and a p r o t e i n r e l a t e d t o c o l l a g e n c a l l e d o t o l i n ( Degens e_t a_l. 1969). O t o l i n c o n s t i t u t e s between 0.25 and 10 p e r cent o f the o t o l i t h . S m a l l amounts of c a l c i u m phosphate and c a l c i u m s u l p h a t e as w e l l as comparable sodium s a l t s are a l s o p r e s e n t ( M o r r i s and K i t t l e m a n 1967). An e x c e l l e n t r e v i e w o f the l i t e r a t u r e on o t o l i t h s and t h e i r growth i s p r e - s e n t e d by R.W. B l a c k e r (1974). D a i l y growth r i n g s were f i r s t r e p o r t e d t o oc c u r i n the o t o - l i t h s o f M e r l u c c i u s b i l i n e a r i s , U t r o p h y c i s chuss and Gadus morhua by P a n n e l l a (1971). Subsequent r e s e a r c h has co n f i r m e d t h e i r o c c u r r e n c e i n a t l e a s t seven s p e c i e s — j u v e n i l e n o r t h e r n anchovy, E n g r a u l i s mordax ( B r o t h e r s e t a_l. 1976 ); j u v e n i l e and a d u l t nehu, S t e l a p h o r u s purpurens ( S t r u s a k e r and Uchiyama 1976); j u v e n i l e s o f the green s u n f i s h , Lepomis c y a n e l l u s , pumpkinseed, 2 F i g u r e 1. The l a b y r i n t h of the cod, Gadus morhua (L.) showing the r e l a t i o n s h i p between the s e m i c i r c u l a r c a n a l s and the o t o l i t h chambers. (a) L e f t l a b y r i n t h viewed from the o u t e r s i d e and (b) d o r s a l view of the l e f t l a b y r i n t h ( a f t e r B l a c k e r 1974). (a) Nerve Ampullae Lapillus Utriculus Sagitta Semi-circular canals Sacculus (b) Nerve Utriculus Lapillus Macula acustica Blood vessel Macula acustica Ampullae Semi-circular canals Asteriscus 3 F i g u r e 2. S a g i t t a e o f 0. n e r k a f r y ( a f t e r T aubert and Coble 1977) S A G I T T A L SECTION 3a D o r s a l E d g e P o s t e r i o r E d g e L A T E R A L V I E W P o s t e r i o r E d g e D O R S A L V I E W V e n t r a l E d g e P r o x i m a l S u r f a c e A n t e r i o r E d g e Nucleus P r o x i m a l S u r f a c e T R A N S V E R S E SECTION D o r s a l E d g e D i s t a l S u r f a c e Nucleus A n t e r i o r E d g e V e n t r a l E d g e D i s t a l S u r f a c e FRONTAL SECTION 4 L . G i b b o s u s , Mozambique mouthbrooder, M e i d i a m e n i d i a ( Barkman 1978); and j u v e n i l e sockeye salmon, Oncorhynchus n e r k a ( W i l s o n and L a r k i n 1980). W i l s o n and L a r k i n (1980) have a l s o observed d a i l y r i n g p a t t e r n s i n the s a g i t t a e of Chinook salmon (Oncorhynchus t s h a w y t s c h a ) , chum salmon (0. k e t a ) , p i n k salmon (0. g o r b u s c h a ) , coho salmon (0. k i s u t c h ) , rainbow t r o u t (Salmo g a i r d n e r i ) , P a c i f i c s t a g h o r n s c u l p i n ( L e p t o c o t t u s a r m a t u s ) , s t a r r y f l o u n d e r ( P l a t i c h t h y s s t e l l a t u s ) , P a c i f i c h a l i b u t ( H i p p o g l o s s u s s t e n o l e p s i s ) , and Olympic mud minnow (Novumbra hubbsi) and i n the a s t e r i s c u s of the n o r t h e r n s q u a w f i s h ( P t y c h o c h e i l u s o r e g o n e n s i s ) . A l t h o u g h d a i l y growth r i n g s were f i r s t r e c o g n i z e d by P a n n e l l a , t h e y were p r o b a b l y f i r s t d e s c r i b e d by H i c k l i n g (1931), who d e s c r i b e d the m i c r o s t r u c t u r e s of the hake ( M e r l u c c i u s m e r l u c c i u s ) o t o l i t h as c o n c r e t e s h e l l s or l a m e l l a e of o r g a n i c m a t e r i a l spaced about two micr o n s a p a r t and connected by s t o u t r a d i a l f i b e r s . The i n o r g a n i c component was d e s c r i b e d as i n t e r l o c k i n g n e e d l e - l i k e c r y s t a l s about 40 micr o n s i n maximum l e n g t h and l e s s than one m i c r o n wide, which are s e c r e t e d among the r a d i a l f i b e r s and pass t h r o u g h the l a m e l l a e . The c o n c e n t r i c l a m e l l a e d e s c r i b e d by H i c k l i n g were examined by P a n n e l l a (1971). P a n n e l l a observed t h a t the s m a l l e s t bands i n the o t o l i t h were made up of two d i s t i n c t p a r t s . Under " o p t i c a l " e x a m i n a t i o n the bands c o n s i s t of a l i g h t zone o f w i d t h 0.5 t o 1 m i c r o n , and a dark zone 0.5 t o 2.5 m i c r o n s wide, w i t h the dark zone c o n t a i n i n g a much denser mesh of o r g a n i c f i b e r s . P a n n e l l a s t a t e s t h a t the dark zone c o r r e s p o n d s 5 t o p e r i o d s o f r a p i d p r o t e i n d e p o s i t i o n , and t h a t " d u r i n g f a s t d e p o s i t i o n the p r o d u c t i o n of o r g a n i c f i b e r s i s h i g h , but c a l c i f i - c a t i o n i s even h i g h e r , so t h a t the r a t i o o f o r g a n i c to i n o r g a n i c f i b e r s i s o v e r w h e l m i n g l y i n f a v o u r of the o r g a n i c p o r t i o n (over 90 p e r cent ) ( S i c ) . D u r i n g slow d e p o s i t i o n fewer o r g a n i c f i b e r s are produced, but the r a t i o i s i n f a v o u r of the o r g a n i c p o r t i o n , s i n c e c a l c i f i c a t i o n i s almost n i l . " T h i s statement may have r e s u l t e d from the o b s e r v a t i o n of both o t o l i t h s and a c e t a t e i m p r e s s i o n s o f o t o l i t h s , and i t i s not c l e a r whether the " o p t i c a l " e x a m i n a t i o n i n v o l v e d the use of t r a n s m i t t e d o r r e f l e c t e d l i g h t . A n o t h e r i n t e r p r e t a t i o n o f these o b s e r v a t i o n s of o t o l i t h com- p o s i t i o n i s p o s s i b l e . In the f o r m a t i o n of the a n n u l u s , i t i s the f a s t growth zone which i s r e l a t i v e l y h i g h i n c a l c i u m c o n t e n t and which i s opaque under o b s e r v a t i o n w i t h t r a n s m i t t e d l i g h t ( B l a c k e r 1971). I n temperate f i s h e s , the f a s t growth zone u s u a l l y forms i n the summer. The h y a l i n e zone u s u a l l y forms i n w i n t e r , i s h i g h e r i n p r o t e i n c o n t e n t ( B l a c k e r 1971, C h r i s t e n s e n 1964), and appears t r a n s p a r e n t under o b s e r v a t i o n w i t h t r a n s m i t t e d l i g h t . S i m i l a r l y , the h y a l i n e p o r t i o n o f a d a i l y r i n g (observed w i t h t r a n s m i t t e d l i g h t ) i s h i g h i n p r o t e i n , analagous to H i c k l i n g ' s l a m e l l a e , i s the t h i n n e s t o f the two zones which comprise a d a i l y r i n g , and i s p r o b a b l y formed d u r i n g the hours of slow f i s h and o t o l i t h growth. The t h i c k e r zone, which appears opaque under t r a n s m i t t e d l i g h t , i s composed p r i m a r i l y o f c a l c i u m s a l t s and i s formed d u r i n g the hours of more r a p i d growth. I s p e c u l a t e t h a t 6 the r a t e o f c a l c i u m s a l t d e p o s i t i o n i s h i g h e s t d u r i n g p e r i o d of most r a p i d o t o l i t h growth, but whether the p r o t e i n l a m e l l a e are formed by a r a p i d i n c r e a s e i n p r o t e i n d e p o s i t i o n , a decrease i n c a l c i u m s a l t d e p o s i t i o n , or a c o m b i n a t i o n of b o t h , cannot be determined by o p t i c a l o b s e r v a t i o n of p r e s e r v e d o t o l i t h s . P a n n e l l a (1974) observed 4, 8, 14, and 28-day c y c l e s i n d a i l y r i n g t h i c k n e s s i n a v a r i e t y of t r o p i c a l f i s h o t o l i t h s , which he a t t r i b u t e d t o l u n a r and t i d a l e f f e c t s . B r o t h e r s and McFarland (unpub ms.) observed a s m a l l number o f French g r u n t (Haemulon f l a v o l i n e a t u m ) o t o l i t h s c o l l e c t e d d u r i n g d i f f e r e n t times of the day. T h e i r o b s e r v a t i o n s suggest t h a t the dark p o r t i o n of the d a i l y growth r i n g ( u s i n g t r a n s m i t t e d l i g h t ) i s formed d u r i n g the n i g h t , and the l i g h t zone i s formed d u r i n g the day. Tau b e r t and Coble (1977) worked w i t h t h r e e s p e c i e s of Lepomis and T i l a p i a mosambica, and attempted to d i f f e r e n t i a t e between the e f f e c t s o f p h o t o p e r i o d and f e e d i n g regime i n d a i l y r i n g f o r m a t i o n . One tank was kept i n c o n s t a n t l i g h t and fed at t h r e e hour i n t e r v a l s . Another was a l s o kept under c o n s t a n t l i g h t and f e d a t t h r e e hour i n t e r v a l s w i t h a nin e hour h i a t u s e v e r y 24 h o u r s . A t h i r d was kept under a 24-hour to 12-hour l i g h t - d a r k c y c l e and fed e v e r y s i x h o u r s , and a f o u r t h was m a i n t a i n e d under a 15-hour t o 9-hour l i g h t - d a r k c y c l e and fed eve r y s i x hours. F i s h i n groups one and two demonstrated no d a i l y r i n g f o r m a t i o n , but i n some cases had as many as f o u r times as many r i n g s as the age i n days. These presumably r e p r e s e n t f e e d i n g r i n g s . Group t h r e e d i d not produce a r i n g e v e r y 36 h o u r s . Taubert and Coble c o n c l u d e d t h a t a d i u r n a l f e e d i n g regime was not s u f f i c i e n t t o cause d a i l y r i n g f o r m a t i o n , and t h a t a d i u r n a l change i n photo- p e r i o d was s u f f i c i e n t t o produce d a i l y r i n g s . They f u r t h e r spe- c u l a t e d t h a t the f i s h under the 24-hour l i g h t to 12-hour dark p h o t o p e r i o d d i d not produce 36-hour r i n g s because the l i g h t c y c l was too abnormal t o e n t r a i n a b i o l o g i c a l c l o c k , and i n f a c t had damping e f f e c t . T aubert and Coble were a l s o a b l e t o s t o p d a i l y r i n g f o r m a t i o n by r e d u c i n g water t e m p e r a t u r e , p r o d u c i n g an a r t i - f i c i a l annulus which resembled the annulus i n w i l d f i s h o t o l i t h s They concluded t h a t d a i l y growth r i n g f o r m a t i o n ceases when f i s h growth c e a s e s . The r e l a t i o n s h i p between d a i l y growth r i n g w i d t h and f i s h growth i s l a r g e l y u n e x p l o r e d . Taubert and Coble found a l i n e a r r e l a t i o n s h i p between s a g i t t a r a d i u s and f i s h l e n g t h (r=0.9936). B r o t h e r s and McFarland (unpub ms.) found a l i n e a r r e l a t i o n s h i p between l o g o t o l i t h r a d i u s and l o g f i s h l e n g t h f o r French g r u n t s and attempted to r e l a t e changes i n d a i l y growth r i n g w i d t h to l i f e h i s t o r y t r a n s i t i o n s . In summary, t h e r e i s much s p e c u l a t i o n and l i t t l e documented e v i d e n c e r e g a r d i n g o t o l i t h growth i n g e n e r a l , and d a i l y growth r i n g f o r m a t i o n i n p a r t i c u l a r . I t i s commonly assumed t h a t the f i n e s t v i s i b l e r i n g s i n any f i s h o t o l i t h are formed d a i l y , p a r - t i c u l a r l y i f they o c c u r i n the f a s t e s t growth zone. I t was the purpose o f t h i s s t u d y : to demonstrate the o c c u r r e n c e of d a i l y growth r i n g s i n the s a g i t t a e o f 0. n e r k a . to examine the r e l a t i o n s h i p between f i s h growth and d a i l y growth r i n g w i d t h . t o d e v e l o p t e c h n i q u e s f o r the o b s e r v a t i o n and measurement d a i l y growth r i n g s . 9 GENERAL METHODS F i s h P r e s e r v a t i o n For t h i s s t u d y , f r y were p r e s e r v e d i n 70 per cent e t h a n o l . For l o n g term s t o r a g e ( s e v e r a l weeks or more) care was taken to ensure t h a t the e t h a n o l had a pH o f a p p r o x i m a t e l y 7, s i n c e a c i d i c p r e s e r v a t i v e s tend t o d e c a l c i f y o t o l i t h s . O t o l i t h Removal Of the t h r e e p a i r s o f o t o l i t h s , o n l y the s a g i t t a e were used. The s a g i t t a e o f l a r g e f i s h are u s u a l l y removed by making a t r a n s - v e r s e c u t t h r e e - q u a r t e r s of the way through the head behind the eye o r b i t s , or l o n g i t u d i n a l l y through the c e n t e r of the head b e t - ween the o r b i t s . For s m a l l f i s h these t e c h n i q u e s are i n e f f i c i e n t . We employed two t e c h n i q u e s depending on the s i z e of the f i s h . The o t o l i t h s o f e x t r e m e l y s m a l l f i s h (1-2 cm.) were removed i n a manner s i m i l a r t o t h a t d e s c r i b e d by Taubert and C o b l e (1977). The head i s p l a c e d or p r e s s e d on a p i e c e of g l a s s on the s t a g e o f a d i s s e c t i n g m i c r o s c o p e . The o t o l i t h s appear as b r i g h t d o t s under s i d e i l l u m i n a t i o n . The head can then be t e a s e d g e n t l y a p a r t u s i n g drawn g l a s s probes and the o t o l i t h s p i c k e d up u s i n g probes or f i n e f o r c e p s . The o t o l i t h s of l a r g e r f r y (>_ 2cm) were removed by h o l d i n g the f r y on the stage of the d i s s e c t i n g m icroscope w i t h the d o r s a l s i d e down and removing the g i l l s and o p e r c u l a r p l a t e s ( F i g . 3 ) . The s a g i t t a e c o u l d then be seen under top i l l u m i n a t i o n j u s t p o s t e r i o r to the eye o r b i t s , and 10 gure 3. Appearance of 0^ n e r k a f r y b e f o r e and a f t e r removal o f lower jaw, g i l l c o v e r s and g i l l s to r e v e a l sag i t t a e . l o w e r j a w , gil.l c o v e r s , g i l l s r e m o v e d 11 were removed by t e a s i n g a p a r t the c a r t i l a g e . O t o l i t h s t o r a g e O t o l i t h s were s t o r e d d r y i n the d e p r e s s i o n s o f M i c r o T e s t 3034 t i s s u e c u l t u r e p l a t e s . Each of the s i x t y d e p r e s s i o n s i n e v e r y p l a t e was numbered and l e t t e r e d f o r c o n v e n i e n c e , and the o t o l i t h s were h e l d i n the d e p r e s s i o n s w i t h a sheet of l / 1 6 t h i n c h p l e x i g l a s s c u t to f i t i n s i d e the p l a t e . The p l e x i g l a s s was h e l d a g a i n s t the d e p r e s s i o n s by a p i e c e of sponge between the l i d and the p l e x i g l a s s , and the e n t i r e u n i t was h e l d t o g e t h e r by s e v e r a l e l a s t i c bands. O t o l i t h P r e p a r a t i o n and O b s e r v a t i o n The o t o l i t h s o f v e r y s m a l l sockeye f r y were examined whole. As the f r y grow, the o t o l i t h s t h i c k e n and the i n t e r n a l s t r u c t u r e becomes o b s c u r e d . T h i c k e r o t o l i t h s were ground i n t o t h i n s ec- t i o n s by a t t a c h i n g them to the c e n t e r o f a g l a s s microscope s l i d e u s i n g a c r y l i c a d h e s i v e . I n i t i a l l y the o t o l i t h s were ground by hand, u s i n g Carborundum No. 50 aluminum o x i d e powder mixed w i t h water on a s i n t e r e d g l a s s p l a t e . Extreme care had to be taken to keep the s l i d e p a r a l l e l to the g r i n d i n g s u r f a c e , and thus a v o i d r o u n d i n g the ground s u r f a c e o f the o t o l i t h . S u b s e q u e n t l y , g r i n d i n g methods developed by John N e i l s o n ( N e i l s o n , I_n P r e s s ) were found to be s u p e r i o r and were used f o r l a t t e r work. N e i l s o n ' s method employs a g r i n d i n g j i g which h o l d s the s l i d e p a r a l l e l t o the g r i n d i n g s u r f a c e to ensure a f l a t g r i n d , and m a i n t a i n s c o n s t a n t and c o n t r o l l a b l e p r e s s u r e . M y l a r g r i n d i n g 12 s h e e t s ( a v a i l a b l e from 3M i n a v a r i e t y of g r i t s i z e s ) were used as the g r i n d i n g s u r f a c e . The f i n e s t g r i t , c a l l e d l a p p i n g paper, had a p a r t i c l e s i z e o f 0.5 m i c r o n s and was used to f i n i s h the o t o l i t h s . Rapid g r i n d i n g was performed on 25 m i cron paper. A f t e r p o l i s h i n g one s i d e of the o t o l i t h , the a c r y l i c g l u e was s o f t e n e d by immersing the s l i d e i n a c e t o n e , and the ground s u r - f a c e o f the o t o l i t h was r e a t t a c h e d to the s l i d e . The g r i n d i n g p r o c e s s was then r e p e a t e d . N e i l s o n a l s o employed heat s e n s i t i v e r e s i n as an a d h e s i v e i n s t e a d o f a c r y l i c . We found t h a t t h i s method i n v o l v e d o n l y s l i g h t h e a t i n g to remove the o t o l i t h s and r e a t t a c h them, and the g r i n d i n g p r o c e s s was g r e a t l y s i m p l i f i e d . The g r i n d i n g p r o c e s s was c r i t i c a l . E x c e s s i v e g r i n d i n g can remove r i n g s from the o t o l i t h , w h i l e i n s u f f i c i e n t g r i n d i n g can l e a v e r i n g s obscured by an overburden of c a l c i u m c a r b o n a t e . The o t o l i t h must be observed numerous times d u r i n g g r i n d i n g , and a f a i r l y h i g h l e v e l o f s k i l l i s r e q u i r e d . S e v e r a l a u t h o r s ( P a n n e l l a 1971; Taubert and Coble 1977; S t r u s a k e r and Uchiyama 1976) have suggested e t c h i n g the ground o t o l i t h s f o r s e v e r a l seconds i n d i l u t e H C l , e i t h e r i n p r e p a r a t i o n f o r t a k i n g an a c e t a t e i m p r e s s i o n , or to augment d i r e c t v i e w i n g . We d i d not use a c e t a t e i m p r e s s i o n s , and found c o n s i d e r a b l e v a r i a t i o n i n e t c h i n g r a t e w i t h i n and between o t o l i t h s e c t i o n s . T h i s v a r i a t i o n r e s u l t e d i n o c c a s i o n a l l o s s e s of m a t e r i a l i n both the c e n t e r and edges of the o t o l i t h . S i n c e t h e r e was o n l y minor improvement i n the v i s i b i l i t y of the i n t e r n a l o t o l i t h s t r u c t u r e , and t h e r e was a p o t e n t i a l f o r i n t r o d u c i n g e r r o r , t h i s t e c h n i q u e was not used f o r r o u t i n e work. 13 The p r e p a r e d o t o l i t h was c l a r i f i e d by immersion i n g l y c e r i n e o r immersion o i l p r i o r t o v i e w i n g . The i n t e r n a l s t r u c t u r e of the o t o l i t h becomes i n c r e a s i n g l y v i s i b l e as the c l a r i f y i n g agent i s absorbed, but e x c e s s i v e c l a r i f i c a t i o n o b s c u r e s the d a i l y growth r i n g s by making the opaque p o r t i o n of the r i n g t r a n s p a r e n t . For salmon f r y o t o l i t h s , s e r i a l counts of d a i l y r i n g s d u r i n g the pr o - c e s s o f c l a r i f i c a t i o n r a p i d l y i n c r e a s e d , then s t a b i l i z e d and then s l o w l y d e c r e a s e d . The counts on v e r y s m a l l o t o l i t h s or v e r y t h i n s e c t i o n s o f o t o l i t h s i n c r e a s e d f o r up to s i x h o u r s , remained s t a b l e f o r s i x to t w e l v e h o u r s , and then decreased f o r s e v e r a l days. I t was a c c o r d i n g l y made s t a n d a r d p r a c t i c e t h a t f o r s m a l l o t o l i t h s c o unts were made a f t e r s i x to e i g h t hours of c l a r i f i c a t i o n . Counts on t h i c k e r s e c t i o n s and l a r g e r o t o l i t h s i n c r e a s e d f o r up to a day, remained s t a b l e f o r s e v e r a l days, and decreased f o r a week or more. O b s e r v a t i o n s were made on these o t o l i t h s on the day f o l l o w i n g immersion. O v e r c l a r i f i e d o t o l i t h s were r e c o v e r e d by p l a c i n g them i n e t h a n o l t o remove the c l a r i f y i n g agent, and r e c l a r i f i e d . The c l a r i f i e d o t o l i t h s were photographed u s i n g an Olympus t r i n o c u l a r compound microscope and t r a n s m i t t e d l i g h t , and f i t t e d w i t h a W i l d 35mm au t o m a t i c camera. O t o l i t h s were photographed at 50X and 200X (based on the m a g n i f i c a t i o n f a c t o r f o r the f i l m n e g a t i v e ) . A p r o j e c t o r s l i d e was pr e p a r e d d i r e c t l y from the f i l m n e g a t i v e and p r o j e c t e d onto a w h i t e t a b l e t o p f o r counts and measurements. A s e r i e s of annotated photographs of sockeye o t o l i t h s has been prepa r e d t o a s s i s t o t h e r s i n i n t e r p r e t i n g d a i l y growth p a t - 14 t e r n s and u n d e r s t a n d i n g the methods used i n i n t e r p r e t i n g the o t o - l i t h s examined i n t h i s s t u d y . These photographs are p r e s e n t e d i n Appendix 1. The methods employed i n c o u n t i n g , measuring and ana- l y s i n g the d a t a are p r e s e n t e d i n the s p e c i f i c methods s e c t i o n s . 15 EXPERIMENT 1: DAILY GROWTH RINGS IN THE OTOLITHS OF JUVENILE SOCKEYE SALMON (Oncorhynchus nerka) I n t r o d u c t i o n . The e a r l y l i f e h i s t o r y o f salmon makes the i n t e r p r e t a t i o n of growth r i n g d a t a d i f f i c u l t . Sockeye eggs h a t c h i n the g r a v e l o f stream beds between December and J a n u a r y , but emergence may not o c c u r u n t i l March, A p r i l or May. F r y g e n e r a l l y move d i r e c t l y to a l a k e upon emergence, but s h o r t - t e r m stream r e s i d e n c y i s not uncommon. P r i o r t o emergence, the f r y e x i s t on y o l k r e s e r v e s ( D i l l 1 968), and exogenous f e e d i n g b e g i n s as y o l k r e s e r v e s are exh a u s t e d . Taubert and Coble (1977) suggest t h a t d a i l y growth r i n g f o r m a t i o n i n the s a g i t t a i s prompted by f l u c t u a t i o n s i n l i g h t i n t e n s i t y and i n f l u e n c e d by temperature. Salmon f r y may o c c u r a t v a r i o u s depths i n the g r a v e l and may be exposed to d i u r - n a l changes i n l i g h t i n t e n s i t y and temperature p r i o r t o emergence. Some sockeye salmon f r y do not b e g i n f e e d i n g even a f t e r c o m p l e t e l y a b s o r b i n g t h e i r y o l k s . Such f r y are c a l l e d " p i n h e a d s " and are commonly observed i n r e a r i n g f a c i l i t i e s . These f a c t o r s may a l l s e r v e to i n c r e a s e the v a r i a t i o n i n the time a t which an i n d i v i d u a l f i r s t produces growth r i n g s and make s u s p e c t the a p p l i c a t i o n t o w i l d p o p u l a t i o n s of r e s u l t s o b t a i n e d from l a b o r a t o r y s t u d i e s . To make t h i s s t u d y of o t o l i t h growth a p p l i c a b l e t o w i l d p o p u l a t i o n s , we c o l l e c t e d and r e a r e d f r y i n t h e i r n a t u r a l environment. 16 Methods Sockeye f r y were c o l l e c t e d from c o n v e r g i n g t h r o a t t r a p s at the mouth o f F u l t o n R i v e r spawning channel 2 a t Babine L a k e , B r i t i s h Columbia, i n 1978. To determine the maximum time between emergence and c a p t u r e at the channel mouth, 10,000 f r y were dyed w i t h n e u t r a l red and r e l e a s e d at the upstream end of the c h a n n e l . E x p e r i m e n t a l f r y were c a p t u r e d i n the l a t e evening and e a r l y morning o f May 12 and 13, and r e a r e d i n e n c l o s u r e s i n the c h a n n e l . Samples were taken on May 13, 23, and 31, and June 9, and were p r e s e r v e d i n 70 p e r cent e t h a n o l . T w e n t y - f i v e f i s h were examined from each sample. One o t o l i t h was used from each f i s h , and any o t o l i t h s which were c r y s t a l l i n e o r o t h e r w i s e uncountable were r e j e c t e d . S a g i t t a e were removed i n the l a b o r a t o r y and a f f i x e d t o g l a s s microscope s l i d e s w i t h the s u l c u s (_i.e. p r o x i m a l s u r f a c e ) upward. T h i c k e r specimens ( p r i m a r i l y those from the June 9 sample) were ground l i g h t l y on the p r o x i m a l s u r f a c e , u s i n g a l u m i - nium o x i d e on a s i n t e r e d g l a s s p l a t e . A l l o t o l i t h s were c l a r i f i e d w i t h g l y c e r i n e and photographed a t a m a g n i f i c a t i o n of 200X u s i n g t r a n s m i t t e d l i g h t and a s t a n d a r d compound microscope w i t h a 35 mm p h o t o g r a p h i c attachment. A 35 mm p r o j e c t o r s l i d e was p r e p a r e d d i r e c t l y u s i n g the developed f i l m n e g a t i v e . R i n g counts were made on the p r o j e c t e d images. A r i n g was d e f i n e d as a p a i r o f d i s t i n c t bands, one l i g h t and one dark. A l l d i s c e r n i b l e r i n g s were counted. F i g u r e 4 shows a prepared o t o - l i t h (from the June 9 sample) and the a s s o c i a t e d count. 17 R e s u l t s Of the 10,000 f r y r e l e a s e d at the upstream end of the c h a n n e l , 340 were r e c a p t u r e d i n sampling at the mouth; 339 were c a p t u r e d w i t h i n 5 h o u r s , and o n l y one s u b s e q u e n t l y , d u r i n g the second e v e n i n g a f t e r r e l e a s e . With such a s h o r t passage of time t h r o u g h the c h a n n e l , the date of c a p t u r e o f the f r y from which o t o l i t h s were sampled may be taken as the date of emergence. I f r i n g s are being formed d a i l y i n sockeye salmon s a g i t t a e , a l e a s t - s q u a r e s l i n e a r r e g r e s s i o n of r i n g count a g a i n s t known age i n days ( a f t e r c a p t u r e ) s h o u l d have a s l o p e of 1. F u r t h e r , i f r i n g f o r m a t i o n began on the average at the time of c a p t u r e , the r e g r e s s i o n s h o u l d s t i l l have a s l o p e of 1 when c o n s t r a i n e d t h r o u g h the o r i g i n . The mean and v a r i a n c e of d a i l y r i n g counts i n samples of 25 sockeye salmon from F u l t o n R i v e r spawning c h a n n e l , Babine Lake, B r i t i s h C olumbia, 1978 were as f o l l o w s : SAMPLE 1 2 3 4 DATE May 13 May 23 May 31 June 9 Mean 3.9565 10.000 17.850 25.668 V a r i a n c e 53.316 58.000 27.503 19.101 B a r t l e t t 1 s t e s t o f homogeneity of v a r i a n c e i n d i c a t e s the v a r i a n - ces o f the f o u r samples are not s i g n i f i c a n t l y d i f f e r e n t . Samples 2, 3, and 4 are d i s t r i b u t e d around a mean which i n each case i s c l o s e t o a l i n e p a s s i n g through the o r i g i n w i t h a s l o p e of 1. 18 gure 4. S a g i t t a e from an 0. n e r k a f r y removed from the e n c l o s u r e on June 9.  19 The counts below the mean i n these samples must be r e p r e s e n t e d i n the f i r s t sample by zer o counts because the v a r i a t i o n below the mean i s not due to c o u n t i n g e r r o r . Because n e g a t i v e counts are i m p o s s i b l e , the f i r s t sample cannot have a mean of zer o and was e l i m i n a t e d from the c o n s t r a i n e d r e g r e s s i o n . One r e g r e s s i o n l i n e was f i t t e d t o a l l the d a t a , and a second r e g r e s s i o n c o n s t r a i n e d t h r o u g h the o r i g i n was f i t t e d t o the data from the l a s t t h r e e samples ( F i g . 5 ) . The s t a t i s t i c s of r e g r e s s i o n of d a i l y r i n g count a g a i n s t time i n days i s as f o l l o w s : S t a n d a r d r e g r e s s i o n ( a l l data) R e g r e s s i o n c o n s t r a i n e d t h r o u g h the o r i g i n ( d a t a f o r May 23, 31) D i s c u s s i o n The r e s u l t s suggest t h a t growth r i n g s i n sockeye salmon s a g i t t a e are formed d a i l y . Because the v a s t m a j o r i t y of f r y m i g r a t e d r a p i d l y and hence were c a p t u r e d almost i m m e d i a t e l y upon emergence, the r e s u l t s f u r t h e r suggest t h a t the average date of f i r s t d i s c e r n i b l e r i n g f o r m a t i o n i s the date of emergence. The apparent r e d u c t i o n i n v a r i a n c e w i t h age can be a t t r i b u t e d both to the death o f the f i s h which do not grow, and to the natu r e of pre-emergent growth r i n g s which are formed w h i l e the f i s h are i n I n t e r c e p t Slope SD o f s l o p e 3.4869 0.81660 0.10020 0.97584 0.033899 20 F i g u r e 5. Graph o f o t o l i t h r i n g count v e r s u s age i n days s i n c e emergence. AO 36- 32- DAYS SINCE EMERGENCE 21 the g r a v e l o f the c h a n n e l . These r i n g s have an e x t r e m e l y f i n e s t r u c t u r e and might be obscured as the o t o l i t h s t h i c k e n ( F i g . 6 ) . A n o t h e r p o s s i b l e e x p l a n a t i o n f o r the r e d u c t i o n of the v a r i a n c e o f r i n g counts w i t h age i s the presence of s u b d a i l y r i n g s at e a r l i e r ages. However, we have not observed s u b d a i l y r i n g s , even i n f i s h r a i s e d i n the l a b o r a t o r y at growth r a t e s s u b s t a n t i a l l y h i g h e r than those o c c u r r i n g i n our e x p e r i m e n t a l e n c l o s u r e s . F i n a l l y , t h e r e i s a p o s s i b i l i t y of f a u l t y t e c h n i q u e s as s o u r c e s of e r r o r t h a t account f o r the r e d u c t i o n of v a r i a n c e w i t h age. R i n g s can be removed from the o t o l i t h s through e x c e s s i v e g r i n d i n g , and can be obscured by the l a y e r o f c a l c i u m overburden where g r i n d i n g i s i n s u f f i c i e n t . Such e r r o r s are not c o n s i d e r e d t o be s e r i o u s f o r sockeye f r y at e a r l y ages as here r e p o r t e d , though they may prove to be at l a t e r s t a g e s of the l i f e h i s t o r y . 22 F i g u r e 6. S a g i t t a e o f an 0. n e r k a f r y removed from the e n c l o s u r e on May 13. 22a 23 EXPERIMENT 2: THE RELATIONSHIP BETWEEN WIDTH OF DAILY GROWTH RINGS IN SAGITTAE AND CHANGE IN BODY SIZE OF SOCKEYE SALMON (Oncorhynchus nerka)FRY I n t r o d u c t i o n O t o l i t h s have been used as a method o f aging f i s h s i n c e the t u r n o f t h i s c e n t u r y (Graham 1929). W h i l e growth s t u d i e s u t i - l i z i n g o t o l i t h s are o f t e n c o n f i n e d t o those s p e c i e s w i t h u n r e a d a b l e s c a l e s , at l e a s t one r e c e n t s t u d y examined the r e l a - t i o n s h i p between f i s h growth and o t o l i t h s i z e i n s a l m o n i d s (Jon s s o n and S t e n s e t h 1977). U n t i l r e c e n t l y , o n l y t e c h n i q u e s u t i l i z i n g a n n u l a r marks were a v a i l a b l e f o r age and growth s t u d i e s . The o c c u r r e n c e of d a i l y growth r i n g s i n t e l e o s t o t o - l i t h s ( P a n e l l a 1971) i n c l u d i n g those of sockeye salmon (Wi l s o n and L a r k i n 1980) p r o v i d e s an i m p o r t a n t new methodology f o r age and growth s t u d i e s . The purpose o f t h i s experiment i s to examine the r e l a t i o n s h i p between f i s h w eight and o t o l i t h s i z e over s h o r t time i n t e r v a l s f o r sockeye salmon f r y , u t i l i z i n g d a i l y r i n g s i n s t e a d of a n n u l i as the time marker. Methods Sockeye salmon f r y were r e a r e d i n the l a b o r a t o r y from f e r - t i l i z e d eggs taken i n the f a l l of 1978 a t the Weaver cre e k spawning c h a n n e l near M i s s i o n , B r i t i s h Columbia. A random sample 24 o f 64 f r y was branded to enable i d e n t i f i c a t i o n o f i n d i v i d u a l s . The marks c o n s i s t e d o f the presence or absence of a c o l d brand i n any one o f f i v e d i s t i n c t l o c a t i o n s on the body. The f r y were a n a e s t h e t i z e d w i t h MS222 and branded w i t h a copper w i r e immersed i n l i q u i d n i t r o g e n . The brand s i t e s were: on the l e f t s i d e above the p e c t o r a l f i n , below the d o r s a l f i n , and above the a n a l f i n , and on the r i g h t s i d e above the p e c t o r a l f i n and below the d o r s a l f i n (see F i g . 7) . These v a r i o u s p a t t e r n s enabled 32 f r y to be i d e n t i f i e d as i n d i v i d u a l s i n each of two t a n k s . Each of the f r y was weighed and branded b e f o r e being p l a c e d i n a tank ( 1 2 i n x 1 2 i n x 2 4 i n ) . One tank was s t o c k e d on June 6, 1979, and a second two days l a t e r . The f i s h were not fed f o r 24 hours p r i o r to w e i g h i n g i n o r d e r to m i n i m i z e v a r i a t i o n i n stomach c o n t e n t s ; o t h e r w i s e the f i s h were f e d a t one hour i n t e r v a l s e i g h t times a day. The use o f a M e t t l e r a u t o m a t i c pan bal a n c e enabled the f i s h to be p l a c e d on the pan, a weight t a k e n , the s c a l e t a r e d and a second weight t a k e n by removing the f i s h from the pan. The two weigh t s were compared to ensure agreement w i t h i n 0.01 grams, and averaged. The f i s h were reweighed i f n e c e s s a r y . The w e i g h i n g s were a l l c a r r i e d out d u r i n g the same p e r i o d o f the day, d u r i n g the l a t e a f t e r n o o n . T h i r t y days a f t e r the f i r s t tank was s e t up, the f i s h i n both tanks were a n a e s t h e t i z e d and reweighed. F r y s u r v i v i n g the second w e i g h i n g were r e a r e d f o r an a d d i t i o n a l two weeks. Data 25 F i g u r e 7. C o l d b r a n d i n g s i t e s on 0. n e r k a f r y . Brand marks Brand marks cn Co 26 were r e c o r d e d f o r those f r y which d i e d i m m e d i a t e l y as a r e s u l t of h a n d l i n g s t r e s s d u r i n g the second w e i g h i n g as w e l l as f o r those s t i l l r e m a i n i n g at the end of the e x p e r i m e n t . Those f i s h which d i e d d u r i n g the course of the experiment were d i s c a r d e d . S a g i t t a e were removed and ground on both s i d e s (see G e n e r a l Methods). One o t o l i t h from each f i s h was photographed u s i n g Kodak panatomic X f i l m i n a 35mm camera mounted on a compound scope. P r o j e c t o r s l i d e s were prepared d i r e c t l y from f i l m n e g a t i v e s . S l i d e s were p r o j e c t e d on a w h i t e t a b l e t op u s i n g a p r o j e c t o r h e l d a t a f i x e d h e i g h t and a n g l e , w i t h a f i x e d f o c u s , t o a c h i e v e a m a g n i f i c a t i o n f a c t o r 382X. Measurements were taken d i r e c t l y from the p r o j e c t e d image. A b r i e f d e s c r i p t i o n of the growth and morphology of sockeye salmon o t o l i t h s w i l l f a c i l i t a t e a d i s c u s s i o n of the measurement system used. F i g u r e 8 r e p r e s e n t s a g e n e r a l i z e d sockeye o t o l i t h . I n sockeye salmon the s a g i t t a t y p i c a l l y has s e v e r a l f o c i , and changes shape as i t grows. The s a g i t t a of the y o l k sac f r y i s o v a l i n shape, but as the f r y grows the s a g i t t a becomes t y p i - c a l l y h e a r t - s h a p e d w i t h the r o s t r u m and p o s t r o s t r u m e x h i b i t i n g the most r a p i d r a d i a l growth. These areas o f g r e a t e s t growth u s u a l l y show the most d i s t i n c t d a i l y r i n g f o r m a t i o n s . The p o s t r o s t r u m i n our samples was l e s s prone to breakage d u r i n g p r e p a r a t i o n , more u n i f o r m l y shaped, and c o n s i s t e n t l y had the most e a s i l y d i s c e r n i b l e d a i l y r i n g p a t t e r n s . To ensure t h a t measurements were taken on the same r a d i u s f o r each o t o l i t h , a l i n e was drawn to the r o s t r u m through the 27 F i g u r e 8. S a g i t t a e o f an 0. n e r k a f r y showing r o s t r u m , p o s t - r o s t r u m , n u c l e i i and l o c a t i o n of p r e f e r r e d r a d i u s .  28 f o c u s i m m e d i a t e l y a d j a c e n t t o t h e p o s t - r o s t r u m . A r a d i u s was d r a w n i n a s t r a i g h t l i n e f r o m t h i s f o c u s t o t h e p o s t - r o s t r a l b u l g e a t a f i x e d a n g l e o f 40 d e g r e e s ( F i g . 8 ) . F o r t h e f i s h f r o m t h e f i r s t t a n k w h i c h s u r v i v e d t o t h e end o f t h e e x p e r i m e n t , t h e r a d i u s was d e t e r m i n e d f o r t h r e e d i s t a n c e s : ( 1 ) f r o m t h e f o c u s t o t h e e d g e o f t h e o t o l i t h ; ( 2 ) f r o m t h e f o c u s t o t h e g r o w t h r i n g 14 r i n g s b a c k f r o m t h e e d g e ; ( 3 ) f r o m t h e f o c u s t o t h e g r o w t h r i n g 44 r i n g s b a c k f r o m t h e e d g e . T h e s e r a d i i c o r r e s p o n d e d t o t h e f i n a l , m i d d l e , and i n i t i a l w e i g h t s r e s p e c t i v e l y . S i m i l a r l y , t h o s e f i s h w h i c h s u r v i v e d t o t h e end o f t h e e x p e r i m e n t f r o m t h e s e c o n d t a n k ( s t o c k e d two d a y s a f t e r t h e f i r s t ) w e r e m e a s u r e d t o t h e e d g e , and t o t h e 1 4 t h and 4 2 n d r i n g s b a c k f r o m t h e e d g e . The o t o l i t h s o f t h o s e f i s h f r o m t h e f i r s t t a n k w h i c h d i e d a s a r e s u l t o f h a n d l i n g s t r e s s were m e a s u r e d t o t h e e d g e and t o t h e r i n g 30 r i n g s b a c k f r o m t h e e d g e . T h o s e f r o m t h e s e c o n d t a n k were m e a s u r e d t o t h e e d g e and t o t h e r i n g 28 r i n g s b a c k f r o m t h e e d g e ( F i g . 9 ) . T h e b r a n d i n g and w e i g h i n g p r o - c e s s l e f t a c l e a r s t r e s s mark 28 o r 30 r i n g s b a c k f r o m t h e e d g e i n e v e r y o t o l i t h ( F i g . 9 ) . I n e a c h c a s e t h e r a d i u s was m e a s u r e d t h r e e i n d e p e n d e n t t i m e s a n d a v e r a g e v a l u e s were c a l c u l a t e d . T h u s , f o r e a c h f i s h t h e r e was d e t e r m i n e d a s e r i e s o f two o r t h r e e w e i g h t s and a s t a n d a r d o t o l i t h r a d i u s c o r r e s p o n d i n g t o e a c h w e i g h t . T h e r e l a t i o n s h i p b e t w e e n o t o l i t h m e a s u r e m e n t s and w e i g h t s o f f r y was e v i d e n t l y c u r v i l i n e a r , a s w o u l d be e x p e c t e d c o n s i d e r i n g 29 F i g u r e 9. S a g i t t a e of 0. nerk a f r y removed from Tank 2 on J u l y 6.  30 t h a t the r e l a t i o n i s between l i n e a r and e s s e n t i a l l y v o l u m e t r i c measurements. A c c o r d i n g l y a s t a n d a r d r e g r e s s i o n l i n e was f i t t e d t o the l o g o f the weight and the l o g o f the r a d i u s . A d d i t i o n a l l y , the d a t a i n raw form were f i t t e d by o r t h o g o n a l p o l y n o m i a l s . The l o g r e g r e s s i o n l i n e was employed to back c a l c u l a t e the weight o f each i n d i v i d u a l f i s h at the time o f p r e v i o u s w e i g h i n g s , u s i n g a l a t e r weight and r a d i u s . The p r e d i c t e d w e i g h t s were com- pared w i t h those o b s e r v e d . The r e l a t i o n s h i p between o t o l i t h measurements and weights of f r y was e v i d e n t l y c u r v i l i n e a r , as would be expected c o n s i d e r i n g t h a t the r e l a t i o n i s between l i n e a r and e s s e n t i a l l y v o l u m e t r i c measurements. A c c o r d i n g l y a s t a n d a r d r e g r e s s i o n l i n e was f i t t e d t o the l o g o f the weight and the l o g o f the r a d i u s . A d d i t i o n a l l y , the d a t a i n raw form were f i t t e d by o r t h o g o n a l p o l y n o m i a l s . R e s u l t s F i s h w e i g h t s and c o r r e s p o n d i n g r a d i i are g i v e n i n Table I . The s t a n d a r d l i n e a r r e g r e s s i o n l i n e f i t t e d t o the logged data had a l i n e o f b e s t f i t £nW = -11.27 + 4.409* &n R and an r 2 of 0.9230 (see F i g . 1 0 ) . A v i s u a l i n s p e c t i o n o f the r e s i d u a l s ( F i g . 1 1 ) showed no marked non-random t r e n d s . A l t h o u g h the data p o i n t s f o r each f i s h are l i n k e d , the c o n s e r v a t i v e assumption was made t h a t a l l d a t a p o i n t s were independent. 31 F i g u r e 10. i n f i s h weight v e r s u s in o t o l i t h r a d i u s f o r i n d i v i - d u a l f i s h (No's 1-29) at the i n i t i a l (June 6 or 8 ) , second ( J u l y 6) and, where a p p l i c a b l e , t h i r d ( J u l y 20) w e i g h i n g . In Otolith Radius 32 F i g u r e 11. P l o t o f r e s i d u a l s from l i n e a r r e g r e s s i o n of In weight on Jin r a d i u s as shown i n F i g u r e 10. 32a Residual o o 4* O p o o " i 1 1 r > a • i r o c • o >• O • T a b l e I Jin o t o l i t h r a d i u s ( JlnR) and Zn f i s h weight ( Jin) f o r e x p e r i m e n t a l f r y at the i n i t i a l (June 6 o r 8 ) , second ( J u l y 6) and t h i r d ( J u l y 20) w e i g h i n g s . F i r s t Weighing Second Weighing T h i r d Weighing Fish# JlnR JlnW JlnR JlnW JlnPl JlnW 1 2. 5014 -0. 31608 2. 7246 0. 63340 2 2. 5479 -0. 18995 2. 7428 0. 80648 3 2. 5408 -0. 20702 2. 7447 0. 99990 4 2. 6174 -0. 22941 2. 7402 0. 92861 5 2. 4874 -0. 21567 2. 7020 0. 81802 6 2. 5088 -0. 36962 2. 7324 0. 60704 7 2. 4973 -0. 27839 2. 7147 0. 86752 8 2. 4681 -0. 30517 2. 6797 0. 68057 9 2. 5518 -0. 25618 2. 7606 0. 78800 10 2. 5233 -0. 20949 2. 7498 0. 83291 11 2. 4423 -0. 51584 2. 6589 0. 49042 12 2. 5080 -0. 45256 2. 7114 0. 58667 13 2. 4510 -0. 52256 2. 6426 0. 30822 14 2. 4891 -0. 39304 2. 6831 0. 73573 15 2. 4553 -0. 45413 2. 6672 0. 57774 16 2. 3842 -0. 63488 2. 6064 0. 30895 17 2. 5392 -0. 45099 2. 7441 0. 65389 18 2. 4441 -0. 47160 2. 5665 0. 40213 19 2. 4570 -0. 67139 2. 6844 0. 61842 20 2. 4380 -0. 52763 2. 6469 0. 51462 2. 7350 0. 70804 21 2. 4380 -0. 56212 2. 6123 0. 18482 2. 6946 0. 60103 22 2. 4204 -0. 38566 2. 6525 0. 67905 2. 7344 0. 87338 23 2. 5031 -0. 43232 2. 6940 0. 66783 2. 7763 0. 91228 24 2. 4562 -0. 39156 2. 6617 0. 72368 2. 7376 0. 97305 25 2. 5337 -0. 02020 2. 7376 0. 88830 2. 8232 1. 0435 26 2. 3979 -0. 66943 2. 6851 0. 61896 2. 7763 0. 87838 27 2. 4998 -0. 21691 2. 7074 0. 68914 2. 7955 0. 75565 28 2. 5193 -0. 25489 2. 7279 0. 84243 2. 8214 1. 1105 29 2. 4105 -0. 27181 2. 6797 0. 79706 2. 7850 1. 0282 34 The o r t h o g o n a l p o l y n o m i a l r e g r e s s i o n y i e l d e d an r ^ o f 0.9157, but the r e s i d u a l s showed a marked non-random t r e n d i n t h a t the we i g h t s of the f i s h w i t h the s m a l l e s t r a d i i were u n d e r e s t i m a t e d . The weight o f each i n d i v i d u a l at the time of p r e v i o u s w e i g h i n g s was back c a l c u l a t e d u s i n g the f o r m u l a : £nW,. = £nW 2 - bUnR^ - InR^) where Wl i s the weight to be e s t i m a t e d W2 i s some l a t e r measured weight R l i s the r a d i u s c o r r e s p o n d i n g t o the weight to be e s t i m a t e d R2 i s the r a d i u s c o r r e s p o n d i n g t o W2 A s i m p l e d e r i v a t i o n f o r t h i s procedure i s g i v e n i n Appendix 1. I t s h o u l d be noted t h a t f o u r d i f f e r e n t s e t s of back c a l c u l a t i o n s are p o s s i b l e w i t h these d a t a . For those f i s h which d i e d a t the second w e i g h i n g , o n l y the i n i t i a l w e ights can be e s t i m a t e d (group A, F i g . 1 2 ) . For those f i s h which s u r v i v e d to the t h i r d w e i g h i n g , the i n i t i a l weight can be c a l c u l a t e d from the wei g h t and r a d i u s c o r r e s p o n d i n g to e i t h e r the middl e or f i n a l w e i g h i n g s (groups B and C, F i g . 1 2 ) , and the middl e weight can be back c a l c u l a t e d u s i n g the f i n a l weight and r a d i u s (group D, F i g . 12 ) . I t s h o u l d be noted f u r t h e r t h a t o n l y the e s t i m a t e of the i n i t i a l w eight based on the middl e weight and r a d i u s (Group B) does not u t i l i z e a r a d i u s measured to the edge o f the o t o l i t h and t h a t back c a l c u l a t i n g the weight at the second weighing u t i l i z e s 35 F i g u r e 12. S a g i t t a e o f 0. n e r k a f r y showing p o s s i b l e types of back c a l c u l a t i o n s of p r e v i o u s f i s h weight u s i n g the c o r r e s p o n d i n g p r e v i o u s o t o l i t h r a d i u s and a l a t t e r f i s h w eight and o t o l i t h r a d i u s as d e s c r i b e d i n the t e x t .  36 a change i n r a d i u s f o r a p e r i o d o f o n l y 14 days (compared w i t h 28-30 and 42-44 days f o r the o t h e r e s t i m a t e s ) . The d i f f e r e n c e between the w e i g h t s e s t i m a t e d by back c a l c u - l a t i o n and the w e i g h t s o b s e r v e d , when p l o t t e d a g a i n s t the n of the p r e d i c t e d weight shows a non-random d i s t r i b u t i o n ( F i g . 1 3 ) . Groups A, B, and C, show a s i m i l a r d e c l i n i n g t r e n d of d i f f e r e n c e s from p o s i t i v e t o n e g a t i v e as f i s h s i z e i n c r e a s e s . A l l but one of the d i f f e r e n c e s i n group D are p o s i t i v e . D i s c u s s i o n Because the r a d i u s measurements were determined p r i m a r i l y on the b a s i s o f d a i l y r i n g c o u n t s , the c l o s e r e l a t i o n s h i p between o t o l i t h r a d i u s and weight as here d e s c r i b e d shows a r e l a t i o n s h i p between the mean w i d t h of a d a i l y r i n g i n sockeye salmon f r y s a g i t t a e , and a mean d a i l y change i n the weight of the f r y . The r ^ v a l u e o f 0.92 f o r the r e g r e s s i o n i s i d e n t i c a l to t h a t d e t e r - mined by J o n s s e n and S t e n s e t h (1978) f o r l o g f i s h l e n g t h v e r s u s l o g o t o l i t h r a d i u s , even though a much s m a l l e r sample s i z e and f i s h s i z e range were used i n our s t u d y . The non-randomness of the d i f f e r e n c e between observed and back c a l c u l a t e d weights of i n d i v i d u a l f i s h i s presumably an e x p r e s s i o n o f some inadequacy of the r e g r e s s i o n model as a r e f l e c t i o n o f the p a t t e r n s of growth, a r e s u l t of measurement e r r o r , or b o t h . A b r u p t changes i n the o t o l i t h growth p a t t e r n o r the f i s h e s w e i g h t may o c c u r . F i s h weight was used here as a measure o f s i z e 37 Figure 13. R e s i d u a l s of back c a l c u l a t e d weights (In back c a l c u - l a t e d f i s h weight - Un observed f i s h weight) versus p r e d i c t e d &n weight. 0.4 0.3 + 0.2 0.1 o ? 0 (/) cr 0.1 1 0.2 0.3 0.4 0.5 • © 9 ® 9 "9 • © 0 9 10 20 30 40 Sample Number 5 0 6 0 7 0 38 because f o r v e r y s m a l l f i s h , weight can be measured much more a c c u r a t e l y than l e n g t h . However, i f the o t o l i t h i s growing i n d i r e c t p r o p o r t i o n t o o t h e r hard p a r t s , a brupt changes i n body form r e s u l t i n g from changes i n growth or t h a t might o c c u r as a r e s u l t o f s t r e s s , c o u l d cause the weight to o t o l i t h r a d i u s r e l a - t i o n s h i p t o d e v i a t e from a l i n e a r l o g - f o r m . There i s a p o s s i b i - l i t y o f time dependent changes i n o t o l i t h r a d i u s . David Levy ( p e r s . comm.) has noted t h a t f o r samples o f chinook salmon f r y s u f f e r i n g from h a n d l i n g s t r e s s , weight decreased and l e n g t h remained c o n s t a n t (over a two week p e r i o d ) , but o t o l i t h growth r i n g s were s t i l l formed d a i l y . A n o t h e r p o s s i b l e cause of the p a t t e r n of d e p a r t u r e of observed from p r e d i c t e d v a l u e s c o u l d be s e l e c t i v e m o r t a l i t y i n the c o u r s e o f the expe r i m e n t . I f s m a l l e r f i s h tend to remain r e l a t i v e l y s m a l l e r and l a r g e r f i s h tend to remain r e l a t i v e l y l a r g e r , then s i z e - s e l e c t i v e m o r t a l i t y at the second weighing c o u l d have c o n t r i b u t e d not o n l y t o the r e l a t i v e l y l a r g e v a l u e of the s l o p e (4.4) but a l s o to the p a t t e r n of d e p a r t u r e s of observed from b a c k - c a l c u l a t e d s i z e s . T h i s does not appear to have been a f a c t o r i n t h i s a n a l y s i s , because the mean i n i t i a l weight of those f i s h which d i e d a t the second w e i g h i n g (0.693 gms) was not s i g n i - f i c a n t l y l e s s than the mean i n i t i a l weight o f the f i s h which s u r - v i v e d t o the end of the experiment (0.700 gms). Measurement e r r o r may be a f a c t o r because the s t a t i s t i c a l p r o c e d u r e of back c a l c u l a t i o n assumes a c o n s t a n t s l o p e . I f measurement e r r o r or o t h e r random e f f e c t s are a s i g n i f i c a n t com- 39 ponent i n the v a r i a t i o n of weight and r a d i u s , t h i s method of back c a l c u l a t i o n w i l l always tend to o v e r e s t i m a t e the p r e v i o u s weight of f i s h w i t h a f o r t u i t o u s l y l a r g e weight to r a d i u s r a t i o , and u n d e r e s t i m a t e those w i t h a f o r t u i t o u s l y s m a l l r a t i o . The back c a l c u l a t i o n f o r m u l a assumes t h a t the f i s h w i l l m a i n t a i n a c o n s t a n t rank o r d e r w i t h r e s p e c t to the weight and o t o l i t h r a d i u s r e l a t i o n s h i p . Changes i n rank o r d e r c o u l d thus generate the p a t - t e r n o f r e s i d u a l s seen f o r groups A, B, and C. By c o n n e c t i n g the p o i n t s r e p r e s e n t i n g the w e i g h t s and c o r r e s p o n d i n g r a d i u s measure- ments f o r the i n d i v i d u a l f i s h (as shown i n F i g . 1 0 ) , i t i s a p p a rent t h a t changes i n rank o r d e r d i d o c c u r . Group D ( F i g . 12 and F i g . 1 3 ) r e p r e s e n t s the p r e d i c t e d weight of f i s h two weeks p r i o r to the end o f the e x p e r i m e n t , as e s t i - mated from f i n a l weight and r a d i u s and the r a d i u s from the f o c u s o f the o t o l i t h t o the growth r i n g 14 r i n g s back from the edge. The p r e c i s i o n o f the weight e s t i m a t e s f o r an i n t e r v a l of two weeks are as good as the e s t i m a t e s f o r the 28-30 and 42-44 day i n t e r - v a l s (groups A and B and group C r e s p e c t i v e l y ) . The c o n s i s t e n t u n d e r e s t i m a t i o n o f p r e v i o u s weight seen i n group D has a number of p o s s i b l e c a uses. S t r e s s r e l a t e d r e d u c t i o n s i n weight to o t o - l i t h r a d i u s r a t i o a t the f i n a l w e i g h i n g (as p r e v i o u s l y d i s c u s s e d ) or measurement e r r o r s a s s o c i a t e d w i t h the edge of the o t o l i t h a c c e n t u a t e d by the s h o r t e r time i n t e r v a l (and hence s m a l l change i n o t o l i t h r a d i u s ) , c o u l d cause the observed d e v i a t i o n i n the r e s i d u a l s . 40 Measurement e r r o r i n weight would appear to be a minor c o n t r i b u t o r , because c o n s e c u t i v e w e i g h t s on each f i s h were seen t o agree w i t h i n 0.01 gms. Measurement e r r o r i s , however, a major component o f the v a r i a t i o n i n r a d i u s v a l u e s . E r r o r s of p l u s o r minus 5 p e r cen t over t h r e e measurements of a r a d i u s were not uncommon. Much of the v a r i a t i o n r e s u l t e d from d i f f i c u l t y d e t e r - m i n i n g the e x a c t l o c a t i o n of the a p p r o p r i a t e f o c u s . Other t e c h - n i c a l problems c o n t r i b u t e d t o v a r i a t i o n i n the r a d i u s measurement; c h i p p i n g or c r a c k i n g o f the o t o l i t h d u r i n g g r i n d i n g o r p r e p a r a t i o n can obscure or s h i f t the apparent l o c a t i o n of the r o s t r u m o r p o s t - r o s t r u m , membranes a d h e r i n g t o the o t o l i t h can obscure the edge of the o t o l i t h , and v a r i a t i o n i n the amount of m a t e r i a l removed d u r i n g g r i n d i n g can change apparent r i n g w i d t h . V a r i a t i o n i n the shape of the o t o l i t h w i t h s i z e , and between i n d i v i d u a l s o f the same s i z e a l s o i n t r o d u c e s v a r i a t i o n i n s t a n - dard r a d i u s measurements, p a r t i c u l a r l y when a r e l a t i v e l y s i m p l e s t a n d a r d method i s employed. For example, because the o t o l i t h changes shape as i t grows, a s t r a i g h t l i n e drawn from the f o c u s t o the o u t s i d e edge of the o t o l i t h w i l l not n e c e s s a r i l y be per - p e n d i c u l a r t o any or a l l o f the r i n g s i t i n t e r s e c t s , nor w i l l i t n e c e s s a r i l y i n t e r s e c t a l l o f the r i n g s at the same a n g l e . The use o f a curved r a d i u s , p e r p e n d i c u l a r t o each r i n g i t i n t e r s e c t s , was c o n s i d e r e d . U n f o r t u n a t e l y , the l e n g t h of a curved l i n e proved d i f f i c u l t t o measure a c c u r a t e l y and d i r e c t l y , and the r e s u l t i n g r a d i u s d i d not always l e a v e the foc u s at the same angle t o the l o n g i t u d i n a l a x i s . Complex age, s i z e and shape s p e c i f i c 41 measurement systems would almost c e r t a i n l y reduce v a r i a t i o n i n r a d i u s measurement, as would improved t e c h n i q u e s of o t o l i t h p r e p a r a t i o n . Appendix 2 g i v e s a s e r i e s of annotated photographs d e s c r i b i n g these and o t h e r t e c h n i c a l problems a s s o c i a t e d w i t h measuring and i n t e r p r e t i n g o t o l i t h s and d a i l y growth r i n g s i n o t o l i t h s . D e s p i t e these s e v e r a l c o n s i d e r a t i o n s i t i s to be emphasized t h a t the r e l a t i o n s h i p between f i s h weight and o t o l i t h r a d i u s p r o - v i d e s a s a t i s f a c t o r y method f o r back c a l c u l a t i o n of weight at p r e v i o u s age. The e r r o r s t h a t a r i s e from the t e c h n i q u e s used are r e l a t i v e l y s m a l l (of the o r d e r of 15 p e r cent) and p e r m i s s i b l e i n p r e d i c t i o n even over as s h o r t a p e r i o d as two weeks. 42 SUMMARY D a i l y r i n g s are found i n the s a g i t t a e of sockeye salmon f r y . Under the c o n d i t i o n s o f n a t u r a l i n c u b a t i o n o b s e r v e d , the f o r - m a tion o f these r i n g s commenced, on average, at the time of emergence. We have found s i m i l a r r i n g f o r m a t i o n s i n the o t o l i t h s o f e v e r y t e l e o s t f i s h o b s e r v e d . The c l o s e r e l a t i o n s h i p between the s i z e of a f i s h , the s i z e of i t s o t o l i t h s and the o c c u r r e n c e of d a i l y r i n g s , a l l o w s the back c a l c u l a t i o n of f i s h weight and, t h e r e f o r e , growth over i n t e r v a l s at l e a s t as s h o r t as two weeks. T h i s shows a r e l a t i o n s h i p between a f i s h ' s change i n weight and the w i d t h o f the c o r r e s p o n d i n g d a i l y growth r i n g . 43 LITERATURE CITED Barkman, R.C. 1978. The use of o t o l i t h growth r i n g s to age young A t l a n t i c s i l v e r s i d e s , M e n i d i a m e n i d i a . T r a n s . Am. F i s h . Soc. 1 0 7 ( 6 ) : 790-792 B l a c k e r , R.W. 1974. Recent advances i n o t o l i t h s t u d i e s . Pages 67-90 I n SEA FISHERIES RESEARCH, F.R. Harden J o n e s , ed. New York: John W i l e y . B r o t h e r s , E.B., C P . Mathews, and B. L a s k e r . 1976. 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SCIENCE 158: 368-70 N i e l s o n J.D. and G.H. Green. 1981. A method o f p r e p a r i n g o t o l i t h s f o r m i c r o s t r u c t u r e e x a m i n a t i o n . Prog. F i s h . C u l t . I n p r e s s . 44 P a n n e l l a , G. 1 9 7 4 . O t o l i t h g r o w t h p a t t e r n s : an a i d i n age d e t e r m i n a t i o n i n t e m p e r a t e and t r o p i c a l f i s h e s . P a g e s 28-39 I n T h e a g i n g o f f i s h . ( T . B . B a g e n a l , ed.) S u r r e y : U n w i n B r o t h e r s , L t d . P a n n e l l a , G. 1 9 7 1 . F i s h o t o l i t h s : d a i l y g r o w t h l a y e r s and p e r i o d i c a l p a t t e r n s . S C I E N C E 1 7 3 : 1124-1127 S t r u s a k e r , P., and J . H . U c h i y a m a . 1976. Age and g r o w t h o f t h e n e h u , S t o l e p h o r u s p u r p u r e n s ( P i s c e s : E n g r a u l i d a e ) , f r o m t h e H a w a i i a n I s l a n d s as i n d i c a t e d by d a i l y g r o w t h i n c r e - m e n t s o f s a g i t t a e . F i s h . B u l l . 74: 9-19. T a u b e r t , B., and D.W. C o b l e . 1977. D a i l y r i n g s i n o t o l i t h s o f t h r e e s p e c i e s o f L e p o m i s and T i l a p i a m o s s a m b i c a . J . F i s h . R e s . B o a r d C a n . 34: 3 3 2 - 3 4 0 . W i l s o n , K e n n e t h H. and P.A. L a r k i n . 1 980. D a i l y g r o w t h r i n g s i n t h e o t o l i t h s o f j u v e n i l e s o c k e y e s a l m o n ( O n c o r h y n c h u s n e r k a ) . C a n . J . F i s h . A q u a t . S c i . 3 7 ( 1 0 ) : 1 4 9 5 - 1 4 9 8 . APPENDIX 1 THE BACK CALCULATION OF PREVIOUS FISH WEIGHT FROM CORRESPONDING PREVIOUS OTOLITH RADIUS AND A LATTER OTOLITH RADIUS AND FISH WEIGHT When a s t r a i g h t l i n e i s f i t t e d t o the da t a f o r l o g f i s h w eight and l o g o t o l i t h r a d i u s , a r e l a t i o n s h i p i s o b t a i n e d of the form: y = a+bx which p r o v i d e s a p r e d i c t i o n o f the mean v a l u e s of y f o r a g i v e n mean v a l u e o f x. To back c a l c u l a t e a v a l u e of y f o r some p r e v i o u s v a l u e of x from a g i v e n s e t o f i n d i v i d u a l v a l u e s of x and y r e q u i r e s an assumption about the c o n s t a n c y of e i t h e r a or b. I f a i s assumed to be an i n v a r i a b l e q u a n t i t y , the l i n e of back c a l c u l a t i o n i s g i v e n by the dashed l i n e i n F i g u r e 1 - l a . A l g e b r a i c a l l y , t h i s i s e q u i v a l e n t t o e s t a b l i s h i n g the p r o p o r t i o n Y 2 -a = X 2 Y1 -a XI The q u a n t i t y b becomes d i f f e r e n t f o r each i n d i v i d u a l c a s e . A l t e r n a t i v e l y , b may be c o n s i d e r e d as i n v a r i a b l e , i n which case f i g u r e 1 - 1 b X 47 the dashed l i n e i n F i g u r e 1 - l b r e p r e s e n t s the l i n e of back c a l c u - l a t i o n and the p r o p o r t i o n a l i t y i s : = b *2 " Xi o r Y 2 - Y i = b ( X 2 - X i ) or Y i - Y 2 = b ( X ! - X 2) The v a l u e o f a i s d i f f e r e n t f o r each i n d i v i d u a l case. The r e l a t i o n between f i s h weight (y) and o t o l i t h r a d i u s (x) was found to be of the form: £n y = a+b &nx In as much as t h e r e was no i n c r e a s e i n v a r i a n c e of Un y w i t h i n c r e a s e d &n x, i t f o l l o w s t h a t the second procedure of assuming a c o n s t a n t s l o p e i s a p p r o p r i a t e . Hence the f o r m u l a f o r back c a l c u l a t i o n : l nWi = £nW 2 - b (£nRi~ £nR 2) 48 APPENDIX 2 ANNOTATED PHOTOGRAPHS OF ONCORHYNCHUS NERKA OTOLITHS AS AN AID TO AGE AND GROWTH ANALYSIS O t o l i t h T h i s f i s h was branded and weighed on June 6, weighed a g a i n 30 days l a t e r , and f i n a l l y weighed and s a c r i f i c e d 44 days a f t e r i n i t i a l w e i g h i n g . The e f f e c t s of s t r e s s of h a n d l i n g are e v i d e n t at r i n g 44 and 14. The r i n g s near the edge are s l i g h t l y o b s c u r e d . ( T h i s problem i s ac c e n t u a t e d by the d i f f i c u l t i e s o f p r i n t i n g a h i g h c o n t r a s t n e g a t i v e . ) "A" shows an area where two r i n g s come t o g e t h e r a l o n g a f a u l t i n the o t o l i t h . F i n d i n g the nu c l e u s i n an o t o l i t h such as t h i s i n v o l v e s c o n s i d e r a b l e u n c e r t a i n t y . P r i o r to r i n g 44, t h i s f i s h was h e l d i n a d e n s e l y p o p u l a t e d tank and fed l e s s r e g u l a r l y ; t h i s i s r e f l e c t e d i n the growth r i n g s . O v e r - c l a r i f i e d and under-ground Under-ground. Note the r i n g of glue seen through the o t o l i t h . T h i s can be m i s t a k e n as a s t r e s s mark by i n e x p e r i e n c e d r e a d e r s . Note a l s o t h a t the r o s t r u m of both o t o l i t h s i s c r y s t a l i n e . 49 Under-ground "A" shows r i n g s l o s t due to e x c e s s i v e c l a r i f i c a t i o n i n g l y c e r i n e . The r i n g s at "B" are d a i l y r i n g s . None o c c u r at "C". The f i r s t d a i l y r i n g would l i k e l y be found near the arrow, a l t h o u g h i t i s d i f f i c u l t to see i t on t h i s p r i n t . Note the r e f r a c t i o n l i n e s near the edge. T h i s i s a f a i r l y t y p i c a l sockeye f r y o t o l i t h p r o - p e r l y ground and c l a r i f i e d . The p r e f e r r e d r a d i u s would s t a r t at the n u c l e u s "A" . Zone "B" shows r i n g s t y p i c a l o f those found d u r i n g p e r i o d s o f i r r e g u l a r growth; extreme care must be t a k e n i n c o u n t i n g r i n g s such as these because each o f the d a r k e r r i n g s can c o n t a i n two or more d a i l y zones. Counts s h o u l d be done at h i g h e r m a g n i f i c a - t i o n than the one shown.  51 52 53 

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