UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Factors affecting precocious sexual development in male rainbow trout Houston, Christopher James Gordon 1981

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

Notice for Google Chrome users:
If you are having trouble viewing or searching the PDF with Google Chrome, please download it here instead.

Item Metadata

Download

Media
831-UBC_1981_A6_7 H69.pdf [ 2.51MB ]
Metadata
JSON: 831-1.0095442.json
JSON-LD: 831-1.0095442-ld.json
RDF/XML (Pretty): 831-1.0095442-rdf.xml
RDF/JSON: 831-1.0095442-rdf.json
Turtle: 831-1.0095442-turtle.txt
N-Triples: 831-1.0095442-rdf-ntriples.txt
Original Record: 831-1.0095442-source.json
Full Text
831-1.0095442-fulltext.txt
Citation
831-1.0095442.ris

Full Text

FACTORS AFFECTING PRECOCIOUS SEXUAL DEVELOPMENT IN MALE RAINBOW TROUT by CHRISTOPHER JAMES GORDON HOUSTON B . S c , U.B.C. 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF ' THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA October 1981 c C h r i s t o p h e r James Gordon Houston, 1981 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 the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t 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 DE-6 (2/79) i i ABSTRACT Rainbow t r o u t (Salmo g a i r d n e r i ) from two w i l d s t o c k s n a t i v e t o B r i t i s h C o lumbia, and a n o n - n a t i v e d o m e s t i c s t r a i n were r e a r e d under v a r y i n g c o n d i t i o n s t o examine e f f e c t s of growth r a t e and body s i z e , g e n e t i c s t o c k , and p h o t o p e r i o d on the i n c i d e n c e and t i m i n g of t e s t i s development. The r a t i o of gonad weight t o body weight (Gonadosomatic index) was found t o be u s e f u l f o r s e p a r a t i n g mature and immature male f i s h and f o r d e t e r m i n i n g the onset of gonadal development. In P r e m i e r l a k e f i s h t e s t i s development began one year b e f o r e the e x p e c t e d d a t e of spawning. At t h i s t i m e , s i g n s of m a t u r a t i o n were e v i d e n t p r i m a r i l y among males t h a t reached a body weight of between t e n and twenty grams, whereas most of the f i s h s m a l l e r than t h i s " c r i t i c a l " s i z e remained immature ( i . e . no t e s t i s developmment). A p p a r e n t l y , t h i s c r i t i c a l s i z e must be re a c h e d by a c e r t a i n time of the y e a r . Thus, a time 'window' e x i s t s wherein f i s h a c h i e v i n g a c e r t a i n s i z e b e g i n p r e p a r a t i o n f o r spawning t h e f o l l o w i n g y e a r . A l t e r i n g p h o t o p e r i o d regime d u r i n g the time window had no e f f e c t on the i n c i d e n c e of s e x u a l p r e c o c i o u s n e s s , but d i d d e l a y s p e r m a t o g e n e s i s by an undetermined l e n g t h of t i m e . i i i TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES i v LIST OF FIGURES v ACKNOWLEDGEMENTS v i INTRODUCTION 1 METHODS 8 INITIATION OF TESTIS DEVELOPMENT 8 EFFECTS OF GROWTH RATE AND DIFFERENT STOCKS 9 EFFECTS OF PHOTOPERIOD ON GONADAL DEVELOPMENT 12 RESULTS 15 INITIATION OF TESTIS DEVELOPMENT 15 EFFECTS OF GROWTH RATES AND DIFFERENT STOCKS 25 EFFECTS OF PHOTOPERIOD ON GONADAL DEVELOPMENT 30 DISCUSSION 34 LITERATURE CITED 41 LIST OF TABLES Ta b l e I . Arrangement of t r e a t m e n t groups and numbers of male rainbow t r o u t r e a r e d a t v a r i o u s p h o t o p e r i o d s 14 T a b l e I I . D a i l y growth s l o p e s c a l c u l a t e d f o r (Body W e i g h t ) 1 ^ 3 vs Time f o r t h r e e s t o c k s of rainbow t r o u t h e l d a t d i f f e r e n t r a t i o n l e v e l s 26 Tab l e I I I . P r o p o r t i o n s of p r e c o c i o u s males found i n t h r e e s t o c k s of rainbow t r o u t r e a r e d a t t h r e e r a t i o n s 28 Tab l e IV. P r o p o r t i o n s of p r e c o c i o u s males and growth s l o p e s f o r rainbow t r o u t at t h r e e r a t i o n l e v e l s 28 T a b l e V. Comparison of mean we i g h t s of mature and immature male t r o u t 30 V LIST OF FIGURES F i g u r e 1. Frequency of GSI v a l u e s i n rainbow t r o u t over s a m p l i n g p e r i o d J u l y 26, 1976 t o F e b r u a r y 23, 1977. 16 F i g u r e 2. Changes i n mean GSI v a l u e s f o r m a t u r i n g male rainbow t r o u t d u r i n g p e r i o d J u l y 26, 1970 t o F e b r u a r y 23, 1977 18 F i g u r e 3. Mean t e s t e s weight (+1SE) of male rainbow t r o u t p l o t t e d a g a i n s t time 19 F i g u r e 4. R e l a t i v e changes i n gonad and somatic growth r a t e s l o p e s over time 20 F i g u r e 5. Frequency d i s t r i b u t i o n s of back c a l c u l a t e d s t a r t up d a t e s and body s i z e s i n m a t u r i n g male rainbow t r o u t 23 v i ACKNOWLEDGEMENTS I would l i k e t o thank the s t a f f of the A b b o t s f o r d h a t c h e r y and p a r t i c u l a r l y M e s s r s . Bob Land, L a r r y M i t c h e l l and Mor l e y Rempel f o r t h e i r c o n s i d e r a b l e t e c h n i c a l a s s i s t a n c e i n the f i s h c u l t u r e , and a l s o S u z i n Crosby f o r h e l p w i t h the h i s t o l o g y . I would a l s o l i k e t o thank Hugh Sparrow f o r both p r a c t i c a l and m o r a l s u p p o r t a t the b e g i n n i n g of the p r o j e c t ; B i n g Sanson f o r her t y p i n g and d r a f t i n g s k i l l s ; E r i c P a r k i n s o n f o r h i s c o n s i d e r a b l e h e l p i n machine p r o d u c t i o n of the t h e s i s and i t s r e v i e w ; my s u p e r v i s o r Don M c P h a i l f o r h i s p a t i e n t support over a l o n g f i v e y e a r s ; and most p a r t i c u l a r l y , A r t Tautz f o r h i s c o n s i s t e n t p r o d d i n g and c o n s i d e r a b l e a s s i s t a n c e i n a n a l y z i n g the d a t a . The F i s h and W i l d l i f e B ranch of the B r i t i s h Columbia M i n i s t r y of Environment p r o v i d e d f i n a n c i a l s u p p o r t f o r t h i s p r o j e c t . F i n a l l y , I thank my w i f e , J e a n n i e , f o r c o n s t a n t encouragements, p r a c t i c a l a s s i s t a n c e w i t h t e d i o u s t e c h n i c a l work and much a p p r e c i a t e d companionship. 1 INTRODUCTION The f a m i l y Salmonidae ( t r o u t , c h a r , and salmon) a r e of c o n s i d e r a b l e economic importance i n N o r t h America and t h e r e i s a l a r g e body of l i t e r a t u r e on t h e i r b i o l o g y and management. However, many of the f a c t o r s c o n t r o l l i n g t h e i r l i f e c y c l e remain u n e x p l o r e d , even i n a r e a s which have i m p o r t a n t commercial and management s i g n i f i c a n c e . Spawning i s an i n t e g r a l p a r t of the t r o u t ' s normal l i f e c y c l e , y e t f o r the f i s h e r y manager i t has u n d e s i r a b l e s i d e e f f e c t s . D u r i n g spawning, t h e r e i s an i n c r e a s e d s u s c e p t i b i l i t y t o b a c t e r i a l and f u n g a l i n v a s i o n s (Simpson, 1976), reduced growth (Nomura, 1963; l i e s , 1974), i n c r e a s e d m o r t a l i t y ( C a m p b e l l , 1971), and a g e n e r a l d e t e r i o r a t i o n i n f l e s h q u a l i t y which makes the f i s h l e s s d e s i r a b l e t o a n g l e r s and commercial f i s h f a r m e r s . T h e r e f o r e , i n c a s e s where n a t u r a l r e p r o d u c t i o n i s u n n e c e s s a r y , as i n s t o c k e d l a k e s or commercial f i s h farms, c o n t r o l over the r e p r o d u c t i v e c y c l e might a l l o w f o r more e f f e c t i v e management and h i g h e r r e t u r n s . The r e p r o d u c t i v e c y c l e s i n f i s h e s i s c o n t r o l l e d by the i n t e r a c t i o n of v a r i o u s f a c t o r s . Under the c o n t r o l of the hypothalamus, the p i t u i t a r y g l a n d r e l e a s e s g o n a d o t r o p i n s s t i m u l a t i n g the development ( i n c r e a s e i n gonad s i z e ) of the gonads ( f o r r e v i e w s see P i c k f o r d and A t z , 1957; Dodd, 1972; Donaldson, 1973). However, the i n t e r n a l mechanism of gonadal development a l s o appears t o be i n f l u e n c e d by changes i n p h o t o p e r i o d and temperature ( f o r r e v i e w s see H a r r i n g t o n , 1959; de V l a m i n g , 1972; de V l a m i n g , 1974). Depending on the s p e c i e s , 2 e i t h e r of the s e c o n t r o l mechanisms may be dominant. In b i r d s and mammals the environment i s known t o a c t as a t r i g g e r but r e p r o d u c t i o n remains p r i m a r i l y under e n d o c r i n e c o n t r o l . In f i s h e s t h e environment a p p a r e n t l y e x e r t s a more p o w e r f u l i n f l u e n c e on the r e p r o d u c t i v e c y c l e (Dodd, 1972). E x p e r i m e n t s w i t h p l a n t s , b i r d s and f i s h have demonstrated t h a t the t i m i n g and f r e q u e n c y of r e p r o d u c t i v e p r o c e s s e s can be m a n i p u l a t e d . For b i r d s and f i s h i t has been shown t h a t e n v i r o n m e n t a l s t i m u l i i n t e r a c t w i t h an i n t e r n a l b i o l o g i c a l rhythm (Schwassman, 1971). However, an endogenous rhythm r e s p o n s i b l e f o r the maintenance of a r e p r o d u c t i v e b e h a v i o u r does not n e c e s s a r i l y e x p l a i n t h e i n i t i a t i o n of gonadal development per se, which must occur a t some time p r i o r t o the onset of r e p r o d u c t i v e b e h a v i o r . , In mammals (humans and r a t s ) , t h e r e i s c o n s i d e r a b l e v a r i a t i o n i n t h e time of p u b e r t y , even under c o n t r o l l e d g e n e t i c and e n v i r o n m e n t a l c o n d i t i o n s . The i n i t i a t i o n of p u b e r t y i s thought t o be a response t o m a t u r a t i o n of the b r a i n - p i t u i t a r y a x i s (Donovan and van der W e r f f t e n Bosch, 1965), which a p p a r e n t l y o c c u r s sooner i n f a s t e r growing i n d i v i d u a l s . Odel and S w e r d l o f f (1972) suggest t h r e e p o s s i b l e e x p l a n a t i o n s ; (1) r e l e a s e of an i n h i b i t o r y mechanism which p r e v e n t s s t i m u l a t i o n of the gonad by the p i t u i t a r y . (2) an i n c r e a s e i n gonadal s e n s i t i v i t y t o p i t u i t a r y p r o d u c t s , or (3) an i n c r e a s e i n p i t u i t a r y s e c r e t i o n s . For f i s h t he p i t u i t a r y i s r e q u i r e d f o r gonadal development ( i n c r e a s e i n s i z e ) , but i t i s not c e r t a i n whether g o n a d o t r o p i n 3 i s n e c e s s a r y f o r m a t u r a t i o n ( p r o d u c t i o n of p r i m a r y s p e r m a t o c y t e s from s p e r m a t o g o n i a ; Hoar, 1969). For p r e s e n t p u r p o s e s , i t i s s u f f i c i e n t t o c o n c l u d e t h a t the p i t u i t a r y i s e s s e n t i a l f o r i n i t i a t i o n of gonadal development and t h a t p r o b a b l y s e p a r a t e p r o c e s s e s c o n t r o l gonadal development and gonadal m a t u r a t i o n . Numerous a u t h o r s have s u c c e s s f u l l y i n d uced p r e c o c i o u s s e x u a l development i n salmon and t r o u t w i t h p u r i f i e d e x t r a c t e d salmon g o n a d o t r o p i n (Funk and Donaldson, 1972; Marushige and D i x o n , 1969; H i r o s e and Donaldson, 1972), but i t i s a p p a r e n t l y more d i f f i c u l t t o d e l a y spawning. X - i r r a d i a t i o n r e t a r d e d gonadal development i n chinook salmon (Bonham and Donaldson, 1972), but t h i s t e c h n i q u e i s p r o b a b l y not u s e f u l i n r o u t i n e f i s h c u l t u r a l programs. S i m i l a r l y hypophysectomy, though s u c c e s s f u l i n p r e v e n t i n g spawning, would be i m p r a c t i c a l on a l a r g e s c a l e , No s i n g l e f a c t o r has been i d e n t i f i e d as c r i t i c a l i n d e t e r m i n i n g age a t f i r s t spawning i n s a l m o n i d s . Rate of growth or f i s h s i z e c o u l d e x e r t an i n f l u e n c e through some p h y s i o l o g i c a l m a t u r a t i o n p r o c e s s but t h e r e a r e a l s o documented g e n e t i c e f f e c t s . There a r e p o s s i b l y s t o c k d i f f e r e n c e s where some s t o c k s mature a t l a t e r ages, as w e l l as an e f f e c t of sex per se, i . e . males o f t e n r e a c h m a t u r i t y one year b e f o r e f e m a l e s . In non-anadromous s a l m o n i d s , t h e r e i s some e v i d e n c e t o suggest t h a t f i s h s i z e i n f l u e n c e s age a t f i r s t spawning, a l t h o u g h i t i s d i f f i c u l t t o s e p a r a t e e f f e c t of s i z e from growth 4 r a t e and g e n e t i c f a c t o r s . Lake t r o u t which had matured e a r l y were found t o be l a r g e f o r t h e i r age and had e x h i b i t e d r a p i d growth (Hanson and W i c k w i r e , 1967). However, brown t r o u t s t o c k s which grew q u i c k l y d i d not mature e a r l i e r than those which grew s l o w l y , a l t h o u g h w i t h i n a s t o c k s l o w e r g r o w i n g , s m a l l e r i n d i v i d u a l s tended t o mature a t a l a t e r age (C a m p b e l l , 1971; McFadden, 1965). A s i m i l a r , r e l a t i o n s h i p between r a p i d e a r l y growth, s i z e , and e a r l y m a t u r a t i o n has been shown f o r rainbow t r o u t (Aim, 1959; Kato , 1975; Oota e t a l . , 1965). Among anadromous sa l m o n i d s the i n f l u e n c e of s i z e on age of f i r s t m a t u r a t i o n i s s i m i l a r t o t h a t found w i t h non-anadromous s p e c i e s . Male chinook salmon mature e a r l i e r i f they a r e f a s t e r g rowing as j u v e n i l e s ( F l a i n , 1970), and B i l t o n (1971) suggested t h a t sockeye salmon r e t u r n e d from the sea e a r l i e r i f they o r i g i n a t e d from l a r g e eggs (which produced l a r g e f r y ) . For p i n k salmon a c c e l e r a t e d i n heated sea-water, the s m a l l p r o p o r t i o n of males which became s e x u a l l y mature w i t h i n t h e i r f i r s t y e a r were somewhat l a r g e r than t h e i r c o n t e m p o r a r i e s (MacKinnon and Donaldson, 1976). Oota et a l . (1965) found i t d i f f i c u l t t o i d e n t i f y a maximum l e n g t h beyond which f i s h always matured but v a r i a b i l i t y i n t h i s c h a r a c t e r i s t i c i s ex p e c t e d when such f a c t o r s as f e e d i n g b e h a v i o u r s , growth r a t e , time of h a t c h i n g , s i z e a t emergence and g e n e t i c v a r i a t i o n a r e c o n s i d e r e d . MacKinnon and Donaldson (1976) p o s t u l a t e d t h a t when male p i n k salmon r e a c h a c r i t i c a l s i z e gonad development s t a r t s and i s then m a i n t a i n e d under e n v i r o n m e n t a l c o n t r o l . In e x a m i n i n g the g e n e t i c component of m a t u r a t i o n , Naevdal 5 et a_l. (1978) r e p o r t e d t h a t f o r A t l a n t i c salmon, v a r i a t i o n i n age a t f i r s t spawning was p r i m a r i l y the r e s u l t of g e n e t i c f a c t o r s . More g e n e r a l l y , i n t e r s p e c i f i c d i f f e r e n c e s a r e known t o e x i s t such as the v a r i a t i o n i n spawning ages between s p e c i e s w i t h s i m i l a r e a r l y l i f e h i s t o r i e s ( e . g . p i n k {2 y e a r s } and chum {4 y e a r s } salmon) and l a t e (4- and 5-year o l d ) and e a r l y m a t u r i n g ( 2 - and 3-year o l d ) s t o c k s of rainbow t r o u t . These d i f f e r e n c e s c o u l d be i n f l u e n c e d by l i f e h i s t o r y t a c t i c s . S t e a r n s (1976) s u g g e s t s t h a t a growing p o p u l a t i o n would tend t o s e l e c t f o r a younger age a t f i r s t r e p r o d u c t i o n , whereas the r e v e r s e s i t u a t i o n i s p o s t u l a t e d f o r a d e c l i n i n g p o p u l a t i o n . S c h a e f f e r and E l s o n (1975) found t h a t mean age a t f i r s t spawning i n c r e a s e s w i t h the d i f f i c u l t y of upstream m i g r a t i o n f o r the anadromous A t l a n t i c salmon. The impact of a heavy f i s h e r y i s a l s o l i k e l y t o s e l e c t a g a i n s t l a r g e r and presumably o l d e r f i s h . Thus, t h e r e a r e s e v e r a l means by which the h e r i t a b l e component of age a t f i r s t spawning might respond t o s e l e c t i v e f o r c e s o p e r a t i n g on d i f f e r e n t s p e c i e s and p o p u l a t i o n s . B e s i d e s e n d o c r i n e , g e n e t i c and growth mechanisms, e n v i r o n m e n t a l v a r i a b l e s a r e known t o i n f l u e n c e the r e p r o d u c t i v e c y c l e . However, v a r i a b l e s such as p h o t o p e r i o d and temperature have been c o n s i d e r e d o n l y i n terms of t h e i r e f f e c t on t i m i n g of spawning r a t h e r than t h e i r i n f l u e n c e upon the i n i t i a t i o n of gonadal development and t h e r e f o r e age a t f i r s t spawning. Jones and Orton (1940) c o n c l u d e d t h a t t emperature was i m p o r t a n t i n c o n t r o l l i n g gonad development i n A t l a n t i c salmon, and T i t a r e v 6 (1974) m a i n t a i n e d t h a t t e m p e r a t u r e was c r i t i c a l i n rainbow t r o u t development. However, i t i s g e n e r a l l y h e l d t h a t t e m p e r a t u r e i s not s i g n i f i c a n t i n c o n t r o l l i n g s e x u a l development (de V l a m i n g , 1972). S i n c e growth i s d i r e c t l y r e l a t e d t o temperature and r a t i o n , any i n f l u e n c e of temperature on m a t u r a t i o n i s p r o b a b l y mediated t h r o u g h i t s e f f e c t on growth r a t e ( B r e t t e t a l . , 1969). P h o t o p e r i o d , however, i n f l u e n c e s the t i m i n g of spawning more d i r e c t l y . Hazard and Eddy (1950) found t h a t a c c e l e r a t i n g p h o t o p e r i o d h a s t e n e d the spawning p e r i o d from a f a l l t o mid-summer. Corson (1955) o b t a i n e d s i m i l a r r e s u l t s , and A l l i s o n (1951) was a b l e t o d e l a y spawning by s i x weeks by e x t e n d i n g t h e day l e n g t h t o a c o n s t a n t 17 hours of l i g h t and 7 hours of d a r k n e s s (17L, 7D). The i n f l u e n c e of p h o t o p e r i o d on immature f i s h i s reviewed by Schwassman (1 9 7 1 ) , who found t h a t gonadal m a t u r a t i o n i n immature green s u n f i s h d i d not r e q u i r e s t i m u l a t i o n by changing day l e n g t h as l o n g as temperature remained h i g h . However, p h o t o p e r i o d s t i m u l a t i o n i s n e c e s s a r y once one p e r i o d of spawning has been completed. Henderson (1963) found t h a t a s i m i l a r c o n d i t i o n seemed t o e x i s t i n t r o u t . However, f o r the purposes of t h i s s t u d y i t was n e c e s s a r y t o e s t a b l i s h whether s p e c i f i c p h o t o p e r i o d c o n d i t i o n s were e s s e n t i a l a t the time when gonad development was i n i t i a t e d , as opposed t o a c t i n g as a t r i g g e r f o r the onset of spawning b e h a v i o r . I n summary, t h i s r e v i e w of t h e l i t e r a t u r e i n d i c a t e s t h a t a v a r i e t y of i n t e r a c t i n g f a c t o r s a r e r e s p o n s i b l e f o r i n i t i a t i o n 7 of gonad development and poses a s e r i e s of q u e s t i o n s t h a t can be examined e x p e r i m e n t a l l y . F i r s t l y , a t what t i m e of the year and a t what s i z e do male rainbow t r o u t i n i t i a t e gonad development by r e d i r e c t i n g energy i n t o g onadal biomass? S e c o n d l y , can i t be e s t a b l i s h e d whether t h e average c r i t i c a l s i z e i s d i f f e r e n t f o r d i f f e r e n t s t o c k s ? I f t h i s were the case such v a r i a t i o n may e x p l a i n the c o n t r o v e r s y i n the l i t e r a t u r e as t o whether e n v i r o n m e n t a l or g e n e t i c e f f e c t s a c t i n g i n d e p e n d e n t l y of e x t e r n a l f a c t o r s a r e the predominant i n f l u e n c e on age a t f i r s t m a t u r i t y . L a s t l y , i s i t p o s s i b l e t o i d e n t i f y and e v a l u a t e t h e r o l e of p h o t o p e r i o d i n terms of i t s c o n t r o l over age a t f i r s t spawning? i 8 METHODS INITIATION OF TESTIS DEVELOPMENT In t h i s experiment t e s t i s development of m a t u r i n g rainbow t r o u t was examined i n r e l a t i o n t o the an n u a l t i m i n g of gonad development. A second o b j e c t i v e was t o de t e r m i n e i f body s i z e was r e l a t e d t o m a t u r a t i o n of i n d i v i d u a l f i s h . A p p r o x i m a t e l y 4500 y e a r l i n g rainbow t r o u t (10—12g) were r e c e i v e d a t A b b o t s f o r d h a t c h e r y i n e a r l y J u l y 1976 and p l a c e d i n 1.2m o v a l f i b r e g l a s s t a n k s ( c a p a c i t y 190 ). The f i s h o r i g i n a t e d from Premier Lake i n e a s t e r n B r i t i s h Columbia and had been r e a r e d by s t a f f a t the Kootenay T r o u t Hatchery near Cranbrook f o r a p p r o x i m a t e l y one y e a r . The e x p e r i m e n t a l t a n k s had a f l o w of 20 1/min from a nearby s p r i n g a t a c o n s t a n t temperature of 9.5° C. F i s h were f e d s e v e r a l t i m e s each day w i t h a commercial f i s h f o o d . B e g i n n i n g on J u l y 26, 1976, and c o n t i n u i n g e v e r y two weeks u n t i l F e b r u a r y 23, 1977, a sample of t h i r t y f i s h was s a c r i f i c e d , t o w e l d r i e d , weighed, measured, and t h e gonads removed. O v a r i e s i n immature f i s h were d i s t i n g u i s h e d by c h a r a c t e r i s t i c o v a l e n l a r g e m e n t s a t the a n t e r i o r p o i n t of attachment. Viewed under low m a g n i f i c a t i o n , t h i s s l i g h t l y e n l a r g e d a r e a of the o v a r y was c l e a r l y g r a n u l a r as compared w i t h the smooth t e x t u r e of the t e s t i s . A f t e r t e s t e s were removed, they were s t o r e d i n 10% f o r m a l i n and l a t e r i n d i v i d u a l l y weighed t o the n e a r e s t O.OOlg. No c o r r e c t i o n was made f o r weight l o s s i n f o r m a l i n but t e s t e s were weighed o n l y a f t e r t h e y had been s t o r e d f o r a t l e a s t two 9 weeks. I t was assumed t h a t a f t e r two weeks no f u r t h e r weight l o s s o c c u r r e d . The gonadosomatic index (GSI) i s a measure of the p e r c e n t a g e of the t o t a l body weight a t t r i b u t a b l e t o gonad m a t e r i a l . As the t e s t e s mature t h e y grow more r a p i d l y than the r e s t of the body and hence the r a t i o of body weight t o t e s t i s w eight changes. The GSI of a s e l e c t e d i n d i v i d u a l f i s h can be c a l c u l a t e d i n two s e p a r a t e ways. Assuming t h a t b o t h gonads a r e of the same s i z e , the GSI r a t i o i s determined as weight of one gonad x 2/body weight x 100 (as i n Funk & Donaldson, 1972). However, Robertson (1958) found t h a t t h e r e was l 0 % - 2 0 % d i f f e r e n c e i n weight between the two t e s t e s and an a l t e r n a t i v e method of c a l c u l a t i o n was recommended: ( t o t a l weight of both t e s t e s / b o d y weight) x 100. The l a t t e r method was used t o i d e n t i f y mature and immature f i s h and e s t a b l i s h the p a t t e r n of t e s t i s and body weight changes w i t h t i m e . EFFECTS OF GROWTH RATE AND DIFFERENT STOCKS The above experiment was a l s o d e s i g n e d t o examine the e f f e c t s of growth r a t e , r a t i o n and g e n e t i c s t o c k on the i n c i d e n c e of p r e c o c i o u s male development. D u r i n g e a r l y J u l y 1976, rainbow t r o u t from two w i l d s t o c k s and one domestic s t r a i n were r e c e i v e d a t the A b b o t s f o r d h a t c h e r y . One w i l d s t o c k was from P r e m i e r Lake, a 229ha l a k e l o c a t e d a t 49° 56'/H5° 30' i n the E a s t Kootenay r e g i o n of B r i t i s h C o lumbia. The l a k e i s a t an e l e v a t i o n of 914m, has a TDS of I79ppm and s e r v e s as a s o u r c e of w i l d s t o c k rainbow t r o u t f o r t h e Kootenay T r o u t H a t c h e r y . The o t h e r w i l d s t o c k was from Pennask Lake which i s 10 l o c a t e d a t 50° 00'/l20° 08' a t an e l e v a t i o n of 1418m. I t has a TDS of 27.0ppm and i s 961ha. Pennask i s a source of eggs f o r the p r o v i n c i a l h a t c h e r y a t Summerland. F i s h from b o t h Pennask and Premier l a k e s n o r m a l l y mature as t h r e e - y e a r - o l d s , but many males a r e a year younger a t f i r s t spawning. The spawning f i s h range from 20-40cm and appear i n the t r i b u t a r y streams j u s t s h o r t l y a f t e r the i c e l e a v e s the l a k e i n the s p r i n g . The domestic s t r a i n has been r e a r e d f o r s e v e r a l g e n e r a t i o n s a t the A b b o t s f o r d h a t c h e r y and i s c h a r a c t e r i z e d by r a p i d growth r a t e s . The d o m e s t i c s n o r m a l l y spawn as t h r e e - y e a r - o l d s and o l d e r i n the f a l l of the y e a r . F i s h from the t h r e e s t r a i n s were a l l a p p r o x i m a t e l y 10-12g i n w e i g ht when r e c e i v e d i n e a r l y J u l y . The Premier and Pennask f i s h were o n e - y e a r - o l d s w h i l e the domestic f i s h were s i x months of age. Each group was r e a r e d i n l o t s of 250 i n e i g h t e e n 1.2m o v a l f i b r e g l a s s t a n k s ( c a p a c i t y 190 ). Water was r e c e i v e d from a s p r i n g which s u p p l i e d water a t a temperature of 9.5° C year round. Each tank was s u p p l i e d w i t h 20 /min of f l o w t h r o u g h o u t the J u l y 8, 1976 t o F e b r u a r y 23, 1977 r e a r i n g p e r i o d . The e x p e r i m e n t a l d e s i g n c o n s i s t e d of e x a m i n i n g the i n c i d e n c e of p r e c o c i o u s development i n t h r e e s t o c k s f e d at t h r e e r a t i o n l e v e l s , w i t h each r a t i o n / s t o c k t r e a t m e n t r e p l i c a t e d once. The r a t i o n f o r each tank was c a l c u l a t e d and measured out d a i l y . The f i s h were then hand f e d s e v e r a l t i m e s each day. Every two weeks a sample of twenty f i s h was removed from each t a n k , l i g h t l y a n e s t h e s i z e d , t o w e l d r i e d , wet weighed and measured; they were then r e t u r n e d t o the tank. From t h e i r 11 mean weight and the number of f i s h i n the tank the d a i l y r a t i o n of 4%, 2%, and 1% body weight/day was c a l c u l a t e d . The s a m p l i n g p r o c e d u r e was the same as f o r t h e f i r s t e x p e r i m e n t s . The sampled f i s h were sexed and c l a s s i f i e d as mature and immature and the t o t a l number of m a t u r i n g male f i s h were r e c o r d e d u n t i l F e b r u a r y 1977 when the experiment was t e r m i n a t e d . A l l mean we i g h t s are g i v e n throughout t h i s paper w i t h one s t a n d a r d e r r o r i n b r a c k e t s (±1SE). Because of t h e i r s i z e and space l i m i t a t i o n s , the f i s h from the above e x p e r i m e n t s t h a t remained on F e b r u a r y 23, 1977 were combined i n t o n i n e groups (no r e p l i c a t e s ) . Each group was kept f o r a v a r y i n g p e r i o d of time t o v e r i f y the m a t u r a t i o n r a t e s of the v a r i o u s t r e a t m e n t f i s h . A l l of the Pennask s t o c k were s a c r i f i c e d on March 21, 1977, a f t e r the d i s c o v e r y of Aeromonas  s a l m o n i c i d a , the c a u s a t i v e agent of f u r u n c u l o s i s . The r e m a i n i n g s i x groups were moved t o a new h o l d i n g f a c i l i t y where the p r e v i o u s l y d e s c r i b e d p r o c e d u r e s were c o n t i n u e d . A n a t u r a l p h o t o p e r i o d was s i m u l a t e d w i t h f l u o r e s c e n t l i g h t s . On May 1, 1977, a l o s s of 70 f i s h (c.40%) was e x p e r i e n c e d from the h i g h r a t i o n P r e m i e r group, but no o t h e r s i g n i f i c a n t l o s s e s o c c u r r e d d u r i n g the e x p e r i m e n t . On August 26, 1977, a l l P r e m i e r and domestic f i s h were k i l l e d and l e n g t h s and w e i g h t s measured. The August 2 6 t h p e r i o d was chosen so t h a t both f a l l and s p r i n g spawners c o u l d be examined t o g e t h e r . 12 EFFECTS OF PHOTOPERIOD ON GONADAL DEVELOPMENT The t h i r d experiment was d e s i g n e d t o examine the e f f e c t s of p h o t o p e r i o d on the i n i t i a t i o n of gonadal development, w i t h a view t o u s i n g p h o t o p e r i o d c o n t r o l i n p r o d u c t i o n h a t c h e r i e s as a means of e l i m i n a t i n g the "window" d u r i n g which s e x u a l development was i n i t i a t e d . The o b j e c t i v e s of the experiment were; 1. To a s c e r t a i n whether or not a d i f f e r e n c e i n the p a t t e r n of development was observ e d between a r t i f i c i a l ( f l u o r e s c e n t ) l i g h t i n g which s i m u l a t e d a n a t u r a l p h o t o p e r i o d , and n a t u r a l ( o u t d o o r ) p h o t o p e r i o d s . 2. To examine t e s t i s development r a t e s f o r f i s h which had been kept on v a r y i n g d u r a t i o n s of 7 l i g h t : 1 7 dark p h o t o p e r i o d s . The l a t t e r experiment was t o i n d i c a t e i f h o l d i n g y e a r l i n g f i s h i n t h e h a t c h e r y on t h e 7 l i g h t : 1 7 dark regime f o r p e r i o d s b r a c k e t i n g the normal p l a n t i n g p e r i o d (June) c o u l d a f f e c t the i n c i d e n c e of p r e c o c i o u s development. On F e b r u a r y 15, 1977, 1800 u n d e r y e a r l i n g rainbow t r o u t of the P r e m i e r Lake s t o c k were s h i p p e d from the Kootenay h a t c h e r y t o the f a c i l i t y a t A b b o t s f o r d . The f i s h were d i v i d e d i n t o 3 groups; n a t u r a l , a r t i f i c i a l n a t u r a l , and s h o r t (seven-hour l i g h t ) , and a f t e r a p e r i o d of o f f s i t e h o l d i n g t o check f o r d i s e a s e and t o a l l o w p r e p a r a t i o n of the tr e a t m e n t a r e a s , the experiment was s t a r t e d on A p r i l 1, 1977. (Note: S h o r t day l e n g t h groups were kept on a 7:17 p h o t o p e r i o d d u r i n g the h o l d i n g p e r i o d , but the a r t i f i c i a l group was on a n a t u r a l c y c l e u n t i l A p r i l 1.) The above groups were f u r t h e r s u b d i v i d e d as 13 o u t l i n e d i n T a b l e I . T a b l e I Arrangement of t r e a t m e n t groups and numbers of male rainbow t r o u t r e a r e d a t v a r i o u s p h o t o p e r i o d s . Group Sub-Group Mark Treatment Numb< N a t u r a l R e p l i c a t e 1 Untagged Outdoors 200 R e p l i c a t e 2 Untagged Outdoors 200 A r t i f i c i a l R e p l i c a t e 1 Untagged F l u o r e s c e n t 200 R e p l i c a t e 2 Untagged F l u o r e s c e n t 200 Sho r t - Tagged 7:17 c o n s t a n t 400 — Tagged Outdoors/May 4 150 — Tagged Outdoors/June 1 200 — Tagged O u t d o o r s / J u l y 4 1 50 Tagged Outdoors/Aug 2 1 00 1800 Due t o a s h o r t a g e of outdoor r e a r i n g space, i t was n e c e s s a r y t o mark i n d i v i d u a l f i s h from the s h o r t t r e a t m e n t groups and combine them i n a s i n g l e 2m outdoor c i r c u l a r pond f o r r e c o v e r y a t the end of the e x p e r i m e n t . I n d i v i d u a l marking was d e s i r a b l e s i n c e i t would p r o v i d e d a t a on the growth r a t e of i n d i v i d u a l f i s h t h a t c o u l d be then r e l a t e d t o t h e i r s e x u a l development. T h i s p r o v i d e d a check f o r the p r e v i o u s e x p e r i m e n t s where s i z e s of f i s h a t v a r i o u s c r i t i c a l t i m e s were back c a l c u l a t e d from the mean growth r a t e f o r each t r e a t m e n t group. A l l f i s h were tagged i n e a r l y May w i t h s m a l l F l o y f i n g e r l i n g t a g s a t t a c h e d t o the d o r s a l s u r f a c e of the f i s h a n t e r i o r t o the 1 4 d o r s a l f i n . A l l f i s h were grown u n t i l September 6, 1977 a t which p o i n t the f i s h were s a c r i f i c e d , wet weighed and measured. T e s t e s were removed from the males and f i x e d i n Bouins f i x a t i v e . A f t e r a minimum of t h r e e weeks, t e s t e s s e l e c t e d f o r h i s t o l o g i c a l e x a m i n a t i o n were embedded i n p a r a p l a s t . The c o o l e d b l o c k s were s e c t i o n e d a t a t h i c k n e s s of 7 m i c r o n s and s e v e r a l f u l l i n t a c t s e c t i o n s mounted on a s i n g l e s l i d e . Once d r y , the t i s s u e was s t a i n e d w i t h h a e m o t o x y l i n and e o s i n and the s l i d e s c l a s s i f i e d f o r stage of development as f o l l o w s : Stage 1 - o n l y spermatogonia p r e s e n t Stage 2 - sper m a t o g o n i a , p r i m a r y and secondary s p e r m a t o c y t e s Stage 3 - sper m a t o g o n i a , s p e r m a t o c y t e s and some spermat i d s Stage 4 - sper m a t o g o n i a , s p e r m a t i d s and many f r e e sperm i n the lumen of the d u c t s Stage 5 - o n l y s p e r m a t i d s and f r e e sperm p r e s e n t Those f i s h c l a s s i f i e d as "stage one" were c o n s i d e r e d immature, whereas any f i s h a t s t a g e s two t o f i v e were c o n s i d e r e d t o be mature or m a t u r i n g . Stage f i v e f i s h were f u l l y , f u n c t i o n a l l y mature males w i t h f r e e f l o w i n g sperm. 15 RESULTS INITIATION OF TESTIS DEVELOPMENT T h i s experiment d e a l t o n l y w i t h P r e m i e r s t o c k and a d d r e s s e d t h r e e problems. The f i r s t problem was t o i d e n t i f y the time of year t h a t t e s t i s development began. The second problem was t o determine the l e n g t h of the time p e r i o d d u r i n g which development was i n i t i a t e d , and the f i n a l problem was t o c a l c u l a t e the s i z e of the f i s h a t the time they began t o mature. P r e v a i l i n g e n v i r o n m e n t a l c o n d i t i o n s were a l s o noted i n r e l a t i o n t o the t i m i n g of the gonadal development. To d i s t i n g u i s h between mature and immature f i s h , a GSI f r e q u e n c y p l o t of the t o t a l sample of male f i s h measured over the e xperiment was made. About a t h i r d of the f i s h (34%) had a GSI v a l u e of l e s s than 0.5 and whereas 63% had GSI's of more than 2.5. Only 3% of a l l f i s h examined had a GSI v a l u e of between 0.5 and 2.5 ( F i g . 1 ) . For the purpose of t h i s a n a l y s i s , t h e r e f o r e , a f i s h was c o n s i d e r e d immature i f i t s GSI was l e s s than 0.5. T h i s method c o r r e c t l y c l a s s i f i e d a l l immature males, but may have a l s o i n c l u d e d w i t h t h a t group a few m a t u r i n g f i s h w i t h GSI's of 0.25-0.50. T h i s e r r o r was p r e f e r r e d t o t h a t which would have i n c l u d e d immature f i s h among the mature. The average GSI v a l u e f o r the immature group was 0.11 (±.007), w h i l e the average f o r the mature groups was 5.6 (± . 3 ) . S i n c e the p r i m a r y c o n c e r n was w i t h f i s h known t o be m a t u r i n g , t h e c o n s e r v a t i v e n a t u r e of the c u t - o f f v a l u e (GSI = 0.5) combined w i t h the s m a l l number of f i s h (3%) i n the q u e s t i o n a b l e range gave an 16 0 . 2 >-O LLI O U J rr LL. 0 .1 0 . 0 2 0 . 0 1 0 . 0 5 0 . 1 0 . 5 2 . 5 5 . 0 G S I V A L U E S 7 . 5 1 0 . 0 F i g . 1. Frequency of o c c u r r e n c e o f gonadosomatic index (GSI) v a l u e s i n rainbow t r o u t ( P r e m i e r s t o c k ) sampled over the p e r i o d June 26, 1976 to F e b r u a r y 23, l'§7 7. GSI v a l u e s o f 0.25 to 2.5 i n d i c a t e o n set o f m a t u r i t y . 17 a c c e p t a b l e method of c l a s s i f i c a t i o n 1 . E x t e r n a l changes i n morphology ( i . e . c o l o r a t i o n , head shape changes, e t c . ) n o r m a l l y a s s o c i a t e d w i t h male spawning s a l m o n i d s were not apparent a t t h i s e a r l y s t a g e . Indeed, not u n t i l the GSI had r i s e n t o a t l e a s t 5.0 c o u l d mature and immature f i s h be s e p a r a t e d on the b a s i s of abdominal shape and then o n l y a f t e r c o n s i d e r a b l e p r a c t i c e and w i t h some e r r o r . . S e v e r a l p a t t e r n s of GSI development over time a r e t h e o r e t i c a l l y p o s s i b l e , depending on the r e l a t i v e growth of the somatic and gonadal components a t d i f f e r e n t t i m e s of the y e a r . Immediately a f t e r s a m p l i n g began on J u l y 23, 1976 r a p i d l y i n c r e a s i n g and h i g h (4.0-8.0) GSI v a l u e s were obse r v e d and by August 24, 1976 the averge GSI had reached a maximum v a l u e (8.3) ( F i g . 2 ) . At t h i s p o i n t , however, an o b v i o u s d e c l i n e was observ e d which c o n t i n u e d t o 5.0 a t the end of t h e e x p e r i m e n t . The GSI d e c l i n e a f t e r l a t e August c o u l d be e x p l a i n e d e i t h e r by the t e s t e s l o s i n g w e i g h t , or a l t e r n a t i v e l y by the body g a i n i n g weight more r a p i d l y than the t e s t i s . A p l o t of gonad weight w i t h time i n d i c a t e d t h a t i n m a t u r i n g f i s h the t e s t i s c o n t i n u e d t o g a i n weight a f t e r the August peak i n GSI a l b e i t a t a l e s s e r r a t e ( F i g . 3 ) . Thus, the t e s t e s underwent a p e r i o d of r a p i d growth b e g i n n i n g sometime p r i o r t o J u l y 26, which c o n t i n u e d u n t ' i l September. F u r t h e r m o r e , as the t e s t i s growth r a t e d e c l i n e d i n e a r l y September, the somatic growth (body w e i g h t - t e s t i s w e i g h t ) i n c r e a s e d n o t i c e a b l y ( F i g . 4 ) . T h e r e f o r e , the t e s t e s d i d not l o s e weight but r a t h e r the d e c l i n e i n GSI i s e x p l a i n e d by changes i n growth r a t e 10.0 LU CO + 1 I I CO -z. < LU 8.0 6.Oh 4.0 'i i 2.01 JUL AUG SEP OCT NOV DEC JAN FEB 26 24 22 21 17 15 12 9 D A T E F i g . 2. Changes i n mean (+1SK) gonadosomatic ind e x (GSI) f o r maturing male rainbow t r o u t (Premier s t o c k ) d u r i n g the time p e r i o d J u l y 26, 1976 to February 23, 1977. co UJ JUL AUG SEP OCT NOV DEC JAN 26 24 22 21 17 15 12 D A T E F i g . 3. Mean t e s t i s weight (+1SE) of male rainbow t r o u t ( P r e m i e r s t o c k ) p l o t t e d a g a i n s t time. T e s t i s weight i n c r e a s e s over the e x p e r i m e n t a l p e r i o d . I-H ^ 1 1 : I : I I L _ MAY JUL AUG SEP OCT NOV DEC 29 26 24 22 21 17 15 D A T E F i g . 4. T r a n s f o r m e d (weight- 1/3) d a t a f o r g o n a d a l and s o m a t i c w e i g h t s showing r e l a t i v e c h a n g e s i n gonad growth r a t e ( s l o p e s ) o v e r t i m e . Cionadosomatic Index (GSI) v a l u e s a r e a l s o i n c l u d e d f o r u n t r a n s f o r m e d d a t a . 21 d i f f e r e n c e s between t e s t i c u l a r and so m a t i c t i s s u e . The above a n a l y s i s i d e n t i f i e d a r a p i d p e r i o d of gonadal growth d u r i n g J u l y and August, but t h e h i g h GSI v a l u e s r e c o r d e d i n the f i r s t s a m p l i n g showed t h a t g o n a d a l development was w e l l underway a t the s t a r t of the ex p e r i m e n t . T h i s n e c e s s i t a t e d an attempt t o 'back c a l c u l a t e ' the time a t which the t e s t e s began i n c r e a s i n g i n weight r e l a t i v e t o the changes i n somatic w e i g h t . To p e r f o r m the back c a l c u l a t i o n , a l i n e a r i z i n g t r a n s f o r m a t i o n f o r somati c weight and t e s t i s weight was r e q u i r e d . H a s k e l l (1948) and l a t e r Iwama and Tautz ( i n p r e s s ) demonstrated t h a t ( w e i g h t 1 / 3 ) produced good l i n e a r r e s u l t s f o r t r o u t growth, a l t h o u g h a l o g t r a n s f o r m or i n s t a n t a n e o u s growth r a t e s c o u l d have been as e a s i l y used. The pr o c e d u r e then was t o measure mean w e i g h t s f o r the somatic and gonadal components of the GSI d u r i n g the r a p i d growth p e r i o d of J u l y 26 t o August 24, l i n e a r i z e the w e i g h t s , and then back c a l c u l a t e the body s i z e and t e s t e s s i z e a t any time p r i o r t o J u l y 26. S i n c e the mean GSI of the immature f i s h was 0.11 (±.007), t h i s v a l u e was used t o i d e n t i f y the date when any of the mature f i s h sampled had begun t e s t i s development. Spec i f i c a l l y , W t l / 3 = WG1/3 + b w t T t l / 3 = T 0 1 / 3 + b t t where 22 Wt = Somatic weight a t time t WD = Somatic weight a t time 0 T t = T e s t i s weight a t time t T Q = T e s t i s weight a t time 0 t = Number of days b = S l o p e of the r e g r e s s i o n of weight 1/3 vs time (days) U s i n g the above a n a l y s i s , a d i s t r i b u t i o n of s t a r t i n g d a t e s was o b t a i n e d . A p p r o x i m a t e l y 30% of the f i s h s t a r t e d t o mature i n the f i r s t two weeks of June and over 70% s t a r t e d i n the 6-week p e r i o d from mid-May t o the end of June ( F i g . . 5 ) . I t was o b s e r v e d , however, t h a t the c a l c u l a t e d v a l u e s were s e n s i t i v e t o the back c a l c u l a t i o n p r o c e d u r e . T h i s was due t o the g e o m e t r i c n a t u r e of the i n c r e a s e ( p a r t i c u l a r l y gonadal w e i g h t ) and the v e r y s m a l l s i z e of the gonads a t s t a r t up t i m e . D e s p i t e t h i s , the p r o c e d u r e d e f i n e d the p e r i o d of a c c e l e r a t e d gonadal growth w i t h i n a c c e p t a b l e l i m i t s . To d e t e r m i n e i f the back c a l c u l a t i o n p r o c e d u r e produced p r e c i s e r e s u l t s , an a n a l y s i s of v a r i a n c e was performed examining s t a r t i n g d a t e s and w e i g h t s as a f u n c t i o n of s a m p l i n g p e r i o d . The ANOVA s h o u l d have d e t e c t e d any b i a s r e l a t e d t o s i z e of f i s h s i n c e the mean w e i g h t s were d i f f e r e n t f o r the d i f f e r e n t sample p e r i o d s . No s i g n i f i c a n t d i f f e r e n c e s were observed and the average s t a r t i n g t i m e s f o r each sample da t e were v e r y s i m i l a r . The average s t a r t i n g d a t e s (±1SE) f o r the t h r e e sample d a t e s of J u l y 26, 1976; August 10, 1976 and August 24, 1976 0 . 3 O Zo . | UJ a UJ cc o . i l 0 M A Y 1 5 3 1 J U N 1 5 3 0 J U L 1 5 STARTING DATE 3 1 1 0 1 5 2 0 2 5 BODY WEIGHT (g) 2 5 + F i g . 5. Frequency d i s t r i b u t i o n s of b a c k c a l c u l a t e d s t a r t up dates and body s i z e s i n m a t u r i n g male rainbow t r o u t ( P r e m i e r s t o c k ) .. 24 were June 17 ( ± 7 d a y s ) , June 16 (±6 days) and June 17 (± 3 d a y s ) , r e s p e c t i v e l y . T h i s a n a l y s i s i n d i c a t e d t h a t t h e time p e r i o d a t which the " d e c i s i o n " t o spawn was made was a p p r o x i m a t e l y one year b e f o r e the date of a c t u a l spawning. F u r t h e r , the absence of any back c a l c u l a t e d v a l u e s b e f o r e May 1, i n d i c a t e d the presence of a d e f i n i t e 'window'. T h i s window was f u r t h e r d e f i n e d by e x a m i n a t i o n of the p r o p o r t i o n of m a t u r i n g f i s h p r e s e n t i n each sample. I t was reasoned t h a t i f f i s h began t o d e v e l o p a c c e l e r a t e d GSI v a l u e s s i m p l y as a f u n c t i o n of r e a c h i n g a c r i t i c a l s i z e and w i t h o u t r e f e r e n c e t o an e n v i r o n m e n t a l l y c o n t r o l l e d 'window', then the p r o p o r t i o n of f i s h m a t u r i n g s h o u l d i n c r e a s e as more f i s h p a s s e d t h e i r c r i t i c a l s i z e . E x a m i n a t i o n of the d a t a , however, i n d i c a t e d t h a t no d e t e c t a b l e i n c r e a s e i n the p r o p o r t i o n of f i s h was obser v e d w i t h t i m e , l e n d i n g f u r t h e r s u pport t o the t h e o r y t h a t a d e f i n i t e 'window' was p r e s e n t d u r i n g the p e r i o d from mid-May t o m i d - J u l y . W i t h the presence of the window and i t s d u r a t i o n d e t e r m i n e d , i t remained t o d e s c r i b e the s i z e of the f i s h and the e n v i r o n m e n t a l c o n d i t i o n s t y p i c a l of t h a t p e r i o d . U s i n g the same pr o c e d u r e of back c a l c u l a t i o n , the body s i z e s of f i s h were c a l c u l a t e d a t the time t h a t the GSI v a l u e was e q u a l t o 0.1 ( F i g . 5 ) . The mean s i z e of the m a t u r i n g f i s h a t t h i s p o i n t was 15.9g (± 0.98). E x a m i n a t i o n of the immature f i s h was more d i f f i c u l t s i n c e t h e r e was no GSI v a l u e t o use as a r e f e r e n c e date on which t o c a l c u l a t e body s i z e . A l s o , o n l y s m a l l numbers of immature f i s h were r e c o r d e d on each sample d a t e . The 25 comparison of mature and immature f i s h was f u r t h e r c o m p l i c a t e d by the p o s s i b l e g e n e t i c a l l y c o n t r o l l e d d i f f e r e n c e s i n growth r a t e which c o u l d e x i s t between the mature and immature groups. In summary, the r e s u l t s of the f i r s t e xperiment i n d i c a t e d t h a t : (1) the GSI began t o a c c e l e r a t e one year p r i o r t o the a c t u a l date of spawning, (2) a d e f i n i t e window l a s t i n g p a r t of May, a l l of June and p a r t of J u l y e x i s t e d , and (3) the average weight of f i s h a t s t a r t i n g time was 15.9g (± . 9 ) . EFFECTS OF GROWTH RATES AND DIFFERENT STOCKS The purpose of t h i s experiment was t o det e r m i n e i f the i n c i d e n c e of p r e c o c i o u s development c o u l d be c o n t r o l l e d by l i m i t i n g growth r a t e s , and s e c o n d l y t o determine i f s t o c k d i f f e r e n c e s were a p p a r e n t . However, i n t e r p r e t a t i o n of the r e s u l t s was confounded by the p o s s i b l e e f f e c t of the d i s e a s e " f u r u n c u l o s i s " on the growth r a t e of the Pennask s t o c k . N e v e r t h e l e s s , d i f f e r e n c e s i n growth r a t e were apparent f o r h e a l t h y domestic and Pr e m i e r s t o c k s , as w e l l as f o r some r a t i o n groups ( T a b l e I I ) . By August 1977, the domestic h i g h r a t i o n group grew t o an average s i z e of 239g, the medium group t o 178g and the low r a t i o n group t o I23g. T h i s c o n t r a s t s markedly w i t h t h e s i z e of t h e Pr e m i e r s t o c k which was 4 7 . l g , 34.3g and 33.8g f o r c o r r e s p o n d i n g r a t i o n s . Thus, f o r whatever r e a s o n , l a r g e d i f f e r e n c e s i n growth r a t e were o b s e r v e d among some groups and i t was p o s s i b l e t o examine the i n c i d e n c e of p r e c o c i o u s development as o r i g i n a l l y p l a n n e d . A n a l y s i s of the p r e c o c i o u s male development i n the above Table I I . Daily growth slopes calculated for (Body Weight) VS Time for three stocks of rainbow trout held at d i f f e r e n t r a t i o n l e v e l s . Ration Stock (% Body Wt/Day) I n i t i a l Weight (g) (± SE) F i n a l Weight (g) (± SE) Regression Slope (± SE) D o m e s t i c Pennask P r e m i e r 4.0 10.6 (1.3) 249.5 (14.8) 1.65 X 1 0 (3.51 X 10 4.0 13.8 (0.6) 228.2 (15:4) 1.65 X 1 0-2 (6.88 x 10 2.0 13.1 (0.9) 170.6 (11.1) 1.38 x 1 0-2 (3.12 X 10 2.0 14.0 (0.5) 185.4. ( 8.2) 1.45 X 1 0-2 (4.04 X 10 1.0 11.5 (0.4) 136.6 ( 8.5) 1.25 X 1 0-2 (4.42 X 10 1.0 11.3 (0.4) 110.2 ( 5.2) 1.16 X 10 2 (6.20 x 10 4.0 10 6 (1.3) 20.3 ( 2.2) 1.73 x 1 0 (3.74 X 10 4.0 10 9 (1.0) 17.0 ( 2.0) 1.31 X 1 0 3 (3.31 X 10 2.0 10 2 (0.6) 18.5 (2.1) 1.92 X 1 0-3 (3.27 X 10 2.0 9 8 (0.9) 17.8 ( 2.7) 2.00 X 1 0-3 (4.60 X 10 1.0 8 0 (0.9) 13.8 ( 1.7) 1.95 X 1 0-3 (5.65 X 10 1.0 10 .1 (1.3) 16.1 ( 3.0) 2.16 X 10 3 "(4.05 X 10 4.0 11 6 (1.2) 46.1 ( 6.6) 4.05 X 1 0 - (8.32 V 10 4.0 19 2 (1.6) 48.2 ( 3.8) 4.86 X 1 0 - (3.69 X 10 2.0 12 5 (1.5) 33.5 ( 4.3) 3.41 X 1 0-3 (4.35 X 10 2.0 13 5 (1.5) 35.0 ( 5.1) 4.39 X 1 0-3 (4 .26 X .10 1.0 12 2 (1.3) 29.8 ( 2.0) 4.11 X 1 0 - (2.66 X 10 1.0 11 8 (1.4) 37.9 ( 4.3) - 4.20 X 10 3 (4.03 X 10 -3, -3| -4! >:! -4: -4 -4, -4' -4 •Si -4! -4! -4: cn 27 groups showed d i f f e r e n c e s dependent on s t o c k and r a t i o n ( T a ble I I I ) . The d o m e s t i c s t r a i n ( f a l l spawning) was found not t o c o n t a i n any m a t u r i n g f i s h a t the t e r m i n a t i o n of the f i r s t e x periment on F e b r u a r y 23, 1977, d e s p i t e the f a c t t h a t t h e i r growth r a t e s were s e v e r a l t i m e s t h a t o b s e r v e d f o r the w i l d f i s h . T h i s i n d i c a t e d e i t h e r t h a t the i n c i d e n c e of p r e c o c i o u s f i s h was much l e s s than i n t h e w i l d s t o c k s or t h a t the t i m i n g of gonadal development was d i f f e r e n t i n t h e s e d o m e s t i c a t e d f a l l spawners. In the second phase of the e x p e r i m e n t , the r e m a i n i n g f i s h from the P r e m i e r and the d o m e s t i c s t o c k were under d i f f e r e n t c o n d i t i o n s i n t h e A b b o t s f o r d f a c i l i t y u n t i l August 23. Sampling of the two s t o c k s a t t h i s time i n d i c a t e d t h a t f o r the Premier s t o c k (c.60%) a s i m i l a r l e v e l of p r e c o c i o u s development was observed t o t h a t r e c o r d e d e a r l i e r . However, the d a t a from the f a l l spawning domestic s t o c k was markedly d i f f e r e n t . In t h i s group, a w e l l d e f i n e d r e l a t i o n s h i p between growth r a t e and i n c i d e n c e of s e x u a l development was observed ( T a b l e I V ) . For the h i g h r a t e s group 5 1 % of t h e male f i s h matured compared w i t h 14% i n the medium r a t e s and 3% i n the low r a t i o n . C l e a r l y , the r a t i o n e f f e c t i n the f a l l spawners was c o n s i d e r a b l e and c o n f i r m e d t h e apparent r e l a t i o n s h i p between f a s t growth, or body s i z e , and r a t e s of p r e c o c i o u s development. From t h e s e r e s u l t s , i t was apparent t h a t t h e f a l l spawning domestic s t o c k behaved i n a d i f f e r e n t manner than the two s p r i n g spawning w i l d s t r a i n s . Whereas the s p r i n g spawners i n i t i a t e d gonad development a t age 1 a p p r o x i m a t e l y one year 28 T a b l e I I I . P r o p o r t i o n s of p r e c o c i o u s males found i n groups of t h r e e s t o c k s rainbow t r o u t r e a r e d from J u l y 1976 a t t h r e e d i f f e r e n t r a t i o n l e v e l s . R a t i o n Number (% Body Number of Number of % Stock wt/Day) Sampled Males Precoc i o u s Males Precoc: P r e m i e r 4.0 75 37 22 59 4.0 75 53 45 85 2.0 75 46 28 61 2.0 75 50 34 68 1 .0 75 56 33 59 1 .0 75 44 25 57 Pennask 4.0 1 60 50 5 10 4.0 86 46 3 7 2.0 1 00 46 2 4 2.0 85 41 3 7 1 .0 1 00 51 2 4 1 .0 75 39 1 3 Domestic 4.0 80 36 0 0 4.0 80 54 0 0 2.0 80 45 0 0 2.0 80 45 0 0 1 .0 80 56 0 0 1 .0 80 44 0 0 p r i o r t o spawning, the f a l l spawners appear t o i n i t i a t e development a t age 1.5 ( i . e . 6 months p r i o r t o spawning). Thus, both s t r a i n s d e v e l o p e d d u r i n g the s p r i n g of the y e a r , but a t d i f f e r e n t ages and a t a d i f f e r e n t time r e l a t i v e t o a c t u a l spawning. A second major d i f f e r e n c e r e l a t e d t o the c r i t i c a l s i z e of the f i s h i n r e l a t i o n t o the p h o t o p e r i o d window d i s c u s s e d e a r l i e r . I t was c l e a r from the d a t a i n Table I I t h a t the mean s i z e s of the low r a t i o n domestic groups (I36.6g and 110.2g) was w e l l above the c r i t i c a l s i z e c a l c u l a t e d f o r the 29 T a b l e IV. P r o p o r t i o n s of p r e c o c i o u s male rainbow t r o u t i n groups from two s t o c k s r a i s e d from J u l y 1976 u n t i l August 1977 a t t h r e e d i f f e r e n t r a t i o n l e v e l s . Growth s l o p e s f o r the p e r i o d F e b r u a r y 1977 t o August 1977 a r e g i v e n . R a t i o n Growth (% Body Slo p e Stock wt/Day) (±1SE) No. of No. of P r e c o c i o u s % Males Males P r e c o c i o u s P r e m i e r Domestic 4% 2% 1% 4% 2% 1% 3.24 (1.10) 3.67 (1 .67) 3.60 (0.93) 13.70 (1.05) 75.40 (1.22) 4.75 (0.93) 34 91 63 35 29 39 20 57 38 18 4 1 59 63 60 51 1 4 3 P r e m i e r s t o c k ( l 0 - 2 0 g ) , y e t o n l y 3% of t h i s group matured. T h i s c l e a r l y i n d i c a t e d a s t o c k dependent c r i t i c a l s i z e of major p r o p o r t i o n s . Throughout the above a n a l y s i s , l a r g e v a r i a t i o n was o b s e r v e d i n the s i z e of f i s h w i t h i n groups t o the degree t h a t many f i s h i n the low r a t i o n groups were l a r g e r than the s m a l l e r f i s h i n the medium and h i g h groups. In t h e , August 26, 1977 sample, the mean w e i g h t s of mature and immature f i s h were compared f o r groups h a v i n g s i g n i f i c a n t numbers of p r e c o c i o u s f i s h ( T a ble V ) . T h i s a n a l y s i s c o n f i r m s the r e s u l t s from the group means and more c l e a r l y demonstrates the v e r y l a r g e d i f f e r e n c e s i n 30 T a b l e V. Comparison of mean w e i g h t s of mature and immature male t r o u t f o r groups h a v i n g s i g n i f i c a n t p r e c o c i o u s development. Mean Weight (g) Stock R a t i o n Mature (n) Immature (n) df t ( c a l c ) P r e m i e r H i g h 91.27 (21) 34.62 (12) 31 5.07** Pre m i e r Medium 87.88 (60) 42.28 (32) 90 6.60** Pre m i e r Low 73.09 (40) 41.98 (25) 63 5.06** Domestic H i g h 755.32 (17) 620.11 (18) 33 2.26* * p < .05 ** p < .01 growth (even w i t h i n groups) which r e l a t e t o s e x u a l development. Thus, t h i s s e t of e x p e r i m e n t s demonstrate the s t r o n g dependence of s e x u a l development on growth r a t e or body s i z e , d i f f e r e n c e s between s t o c k s r e l a t e d t o both h e r i t a b l e c a p a b i l i t y f o r f a s t growth and d i f f e r e n c e s i n c r i t i c a l s i z e , and f i n a l l y the d i f f e r e n t s t r a t e g y shown by f a l l spawners i n which the same cues a r e used f o r i n i t i a t i o n of gonadal development but a t a d i f f e r e n t s tage i n t h e i r l i f e h i s t o r y r e l a t i v e t o spawning. EFFECTS OF PHOTOPERIOD ON GONADAL DEVELOPMENT The f i r s t o b j e c t i v e of t h i s experiment was t o d e t e r m i n e whether the i n c i d e n c e and s t a g e s of development f o r n a t u r a l p h o t o p e r i o d and s i m u l a t e d n a t u r a l groups were the same. For the 200 f i s h i n each of the f o u r groups, the p r o p o r t i o n of m a t u r i n g males was 27% and 34% i n the outdoor t a n k s and 33% and 44% i n the i n d o o r s i m u l a t e d t r e a t m e n t s . While t h e r e were some 31 d i f f e r e n c e s between groups, they were w i t h i n the range of e x p e c t e d v a r i a t i o n and were not s i g n i f i c a n t l y d i f f e r e n t i n a C h i square a n a l y s i s . A l t h o u g h not s i g n i f i c a n t , t h e s e d i f f e r e n c e s can be u n d e r s t o o d by e x a m i n a t i o n of the mean w e i g h t s of the male f i s h i n each of the f o u r groups. The group w i t h the h i g h e s t p r o p o r t i o n of males a l s o had the h i g h e s t mean weight (44% p r e c o c i o u s and 2 6 . 0 l g (± 3.08)). S i m i l a r l y , the two groups w i t h the l o w e s t p r o p o r t i o n s of mature males (27% and 33%) a l s o had the lo w e s t mean weigh t s 22.63g (± 2.22) and 20.47g (± 2.09), r e s p e c t i v e l y . The h i s t o l o g i c a l a n a l y s i s of t h e s e groups i n d i c a t e d no d i f f e r e n c e s i n stage of development and from 32 samples from the i n d o o r groups and 44 samples from the outdoor groups, almost a l l the i n d i v i d u a l s (91% and 95%, r e s p e c t i v e l y ) showed the l a t e r s t a g e s 4 and 5 of sp e r m a t o g e n e s i s . In summary, i t can be c o n c l u d e d t h a t the s i m u l a t e d n a t u r a l p h o t o p e r i o d t r e a t m e n t was i n a l l d i s c e r n a b l e ways s i m i l a r t o the o u t s i d e n a t u r a l p h o t o p e r i o d t r e a t m e n t . Major d i f f e r e n c e s i n development were e x p e c t e d i n a comparison between f i s h m a i n t a i n e d on a c o n s t a n t seven-hour l i g h t c y c l e and tho s e i n the n a t u r a l and s i m u l a t e d n a t u r a l g roups. Some of the tagged f i s h i n the seven-hour group l o s t t h e i r t a g s d u r i n g the e x p e r i m e n t , but s u f f i c i e n t f i s h were s t i l l a v a i l a b l e t o a l l o w c o m p a r i s o n . The i n c i d e n c e of p r e c o c i o u s development between the two tr e a t m e n t groups was not s i g n i f i c a n t u s i n g a C h i square a n a l y s i s even though f i s h r a i s e d on n a t u r a l p h o t o p e r i o d s appeared t o have s u b s t a n t i a l l y more mature f i s h (19% f o r seven-hour and 32% f o r n a t u r a l ) . 32 S i m i l a r l y , t h e r e was no d i f f e r e n c e i n the p e r c e n t a g e mature between a l l those f i s h t r e a t e d w i t h a seven-hour l i g h t p h o t o p e r i o d and l a t e r exposed t o n a t u r a l p h o t o p e r i o d , and the c o n t r o l s . I t i s c o n c l u d e d , t h e r e f o r e , t h a t p h o t o p e r i o d t r e a t m e n t s c o u l d not be demonstrated t o a f f e c t the i n c i d e n c e of p r e c o c i o u s s e x u a l development. I t was p o s s i b l e t h a t p h o t o p e r i o d c o u l d a f f e c t growth per  se and s e c o n d a r i l y , p r e c o c i o u s development. However,the d i f f e r e n c e s i n f r e q u e n c y which were obser v e d c o u l d not be e x p l a i n e d on the b a s i s of s i z e a l o n e . Of a l l groups, the f i s h r a i s e d on seven hours of l i g h t were the second l a r g e s t f i s h 41.06g (± 3.47), but had the second l o w e s t f r e q u e n c y of p r e c o c i o u s males ( 1 9 % ) . Even so, i n a l l n i n e t r e a t m e n t groups the f i s h found t o be mature a t t h e end of the experiment were s i g n i f i c a n t l y l a r g e r (p < .05), both a t the b e g i n n i n g of the experiment and a t the end, than the immature males. T h i s f u r t h e r s u p p o r t s the p r e v i o u s s u g g e s t i o n t h a t mature f i s h a r e l a r g e r or a t l e a s t have grown f a s t e r . However, a seven-hour l i g h t p h o t o p e r i o d does not s i g n i f i c a n t l y change the i n c i d e n c e of p r e c o c i o u s s e x u a l development. The r e s u l t s of the h i s t o l o g i c a l e x a m i n a t i o n p r o v i d e d e v i d e n c e t h a t , a l t h o u g h a seven-hour l i g h t p h o t o p e r i o d does not change the i n c i d e n c e of p r e c o c i o u s development, i t does d e l a y t h e p r o c e s s of s p e r m a t o g e n e s i s . At t h e end of t h e experiment c o n t r o l f i s h on n a t u r a l p h o t o p e r i o d were p r i m a r i l y a t s t a g e s f o u r and f i v e ( 9 0-95%); t h a t i s , l a r g e numbers of s p e r m a t i d s a r e p r e s e n t and the breakdown of the t e s t i s s t r u c t u r e towards a 33 f u l l y f u n c t i o n a l male was imminent or complete. By c o n t r a s t , i n the f i s h on a c o n s t a n t seven-hour l i g h t p h o t o p e r i o d none had reached t h e s e s t a g e s and a l l m a t u r i n g males were a t s t a g e s two and t h r e e . As e x p e c t e d , by the end of August t h o s e f i s h removed from seven-hour l i g h t t o a n a t u r a l p h o t o p e r i o d i n May and June were now p r e d o m i n a t e l y a t s t a g e s f o u r and f i v e ( 7 1 % and 100%, r e s p e c t i v e l y ) . The f i s h exposed t o a n a t u r a l p h o t o p e r i o d i n J u l y and August were somewhat b e h i n d and on average had 59% a t s t a g e s two and t h r e e , and 41% a t s t a g e s f o u r and f i v e . T h e r e f o r e , i t i s c o n c l u d e d t h a t h o l d i n g rainbow t r o u t u n d e r y e a r l i n g s on a seven-hour l i g h t p h o t o p e r i o d d u r i n g the time t h a t a " d e c i s i o n t o spawn" the f o l l o w i n g y e a r was made d i d not change the p r o p o r t i o n of males which p r e c o c i o u s l y mature. R a t h e r , such a p h o t o p e r i o d t r e a t m e n t d e l a y e d s p e r m a t o g e n e s i s . I t i s not known from these e x p e r i m e n t s whether such a d e l a y i s c r i t i c a l t o s u c c e s s f u l spawning the f o l l o w i n g y e a r . 34 DISCUSSION The purpose of the above e x p e r i m e n t s was t o examine the e f f e c t s of growth r a t e , r a t i o n , g e n e t i c s t o c k and p h o t o p e r i o d on t h e i n i t i a t i o n of gonadal development and the subsequent m a t u r a t i o n of the t e s t i s i n t o a f u n c t i o n a l l y mature form. The f i r s t experiment d e f i n e d the p e r i o d d u r i n g which gonad development was s t a r t e d f o r b o t h s p r i n g and f a l l spawners. For t h e s p r i n g spawners, the r a t i o of body weight t o gonad weight (GSI) began t o i n c r e a s e d u r i n g the p e r i o d between l a t e May and e a r l y J u l y , which f o r Premier Lake f i s h i s e x a c t l y one year p r i o r t o the peak of the spawning run o c c u r r i n g i n mid-June. For f a l l spawners, gonads began t o d e v e l o p a t a p p r o x i m a t e l y the same time of y e a r but at an age of 1.5 y e a r s . Thus, the r e q u i r e d p e r i o d f o r r e a c h i n g f i n a l gonad s i z e was a maximum of s i x months f o r the f a l l spawners and one year f o r the s p r i n g spawners. However, e x a m i n a t i o n of the p a t t e r n of development f o r the s p r i n g f i s h r e v e a l e d a d e c l i n e i n GSI a f t e r August, w h i c h upon f u r t h e r a n a l y s i s was found t o r e s u l t from a d e c l i n e i n t e s t i s growth r a t e , accompanied by an i n c r e a s e i n somatic growth r a t e . Thus, a p p r o x i m a t e l y a f o u r - t o six-month p e r i o d of growth was r e q u i r e d f o r the t e s t i s t o r e a c h u l t i m a t e s i z e i n b o t h s p r i n g and f a l l spawners. The d i f f e r e n c e was t h a t i n the s p r i n g f i s h , the six-month p e r i o d of growth was f o l l o w e d by a s i x - m o n t h p e r i o d of r e l a t i v e dormancy whereas i n t h e f a l l f i s h , g o n a d a l development was f o l l o w e d i m m e d i a t e l y by spawning. The e f f e c t of t h i s s t r a t e g y i s t h a t the f i s h a r e a b l e t o d i r e c t energy i n t o b o t h gonadal and s o m a t i c growth d u r i n g the p e r i o d 35 of the year when c o n d i t i o n s f o r growth a r e a p p r o p r i a t e . The f a c t t h a t the i n i t i a t i o n of development o c c u r s d u r i n g the p e r i o d from l a t e May t o e a r l y J u l y , j u s t b e f o r e the s e a s o n a l maximum of food abundance, i s c o n s i s t e n t w i t h the g e o m e t r i c n a t u r e of growth of the gonads. In o t h e r words, s i n c e energy r e q u i r e d f o r growth i s a f u n c t i o n of the s i z e of the t e s t i s , the commencement of gonadal development must occur e a r l y i n t h e year i f the major growth phase i s t o occur d u r i n g p e r i o d s of warm te m p e r a t u r e s and s u f f i c i e n t f o o d . However, i t i s p o s s i b l e t h a t the d e c l i n e i n GSI a f t e r August was more pronounced under t h e s e l a b o r a t o r y c o n d i t i o n s . In the w i l d , the s t a b l e f o o d r a t i o n a v a i l a b l e i n the h a t c h e r y i s not a r e a l i t y and i n n a t u r e the GSI p a t t e r n may w e l l not i n c l u d e a drop i n GSI b r o u g h t about by d e c l i n i n g t e s t i s growth r a t e s and e l e v a t e d somatic growth. R a t h e r , as w i n t e r encroaches the somatic growth would be e x p e c t e d t o d e c l i n e w i t h the t e s t i s growth and as a r e s u l t t h e GSI would not change a p p r e c i a b l y . The p r e s e n c e of "time window" f o r the i n i t i a t i o n of t e s t i s development was c o n f i r m e d by the r e s u l t s of the f i r s t e x p e r i m e n t s s i n c e the p r o p o r t i o n of m a t u r i n g f i s h d i d not change s i g n i f i c a n t l y d u r i n g the c o u r s e of the e x p e r i m e n t . F u r t h e r m o r e , many f i s h which were obse r v e d t o r e a c h the apparent c r i t i c a l s i z e l a t e r i n the year d i d not d e v e l o p s e x u a l l y . The f i r s t experiment e s t a b l i s h e d the p r e s e n c e of a window, w h i l e the second experiment was d i r e c t e d towards d e t e r m i n i n g the f a c t o r s i n f l u e n c i n g the i n i t i a t i o n of t e s t i s development 36 d u r i n g the time window. R e s u l t s of the r a t i o n e x p e r i m e n t s c l e a r l y demonstrated the importance of body s i z e as the v a r i a b l e a s s o c i a t e d w i t h development. T h i s g i v e s credence t o the s u g g e s t i o n of Mackinnon and Donaldson (1976) t h a t p r e c o c i o u s s e x u a l development i n male p i n k salmon may be s i z e r e l a t e d and t h a t once f i s h r e a c h a c r i t i c a l s i z e gonad development i s i n i t i a t e d . I n the domestic s t r a i n l a r g e d i f f e r e n c e s i n the i n c i d e n c e of p r e c o c i o u s development were observ e d as a f u n c t i o n of r a t i o n and body s i z e . R e s u l t s from the o t h e r s t o c k s were l e s s c l e a r due t o the f a i l u r e of the r a t i o n t r e a t m e n t s t o produce the c o n s i s t e n t d i f f e r e n c e s i n s i z e among groups observed i n the domestic s t o c k . D e s p i t e t h e s e d i f f e r e n c e s the e v i d e n c e d i d s u p p o r t the concept t h a t l a r g e r f i s h were more l i k e l y t o mature. A comparison of the average s i z e of mature and immature f i s h , independent of r a t i o n t r e a t m e n t was u n e q u i v o c a l i n d e m o n s t r a t i n g the a s s o c i a t i o n of f i s h s i z e w i t h t e s t i s development. Back c a l c u l a t i o n s f o r the P r e m i e r s t o c k suggested t h a t the c r i t i c a l s i z e range was betwen 1Og and 20g f o r the p e r i o d l a t e May t o e a r l y J u l y . Thus, f i s h s m a l l e r than t h i s s i z e a t t h a t time would not be e x p e c t e d t o mature i f s i z e was the o n l y d e t e r m i n i n g v a r i a b l e . The above c o n c l u s i o n was s u p p o r t e d by the r e s u l t s from the Pennask s t o c k s i n c e most of t h e f i s h were below t h e c r i t i c a l s i z e f o r Premier f i s h and a v e r y low i n c i d e n c e of m a t u r a t i o n was o b s e r v e d . C l e a r l y , d i f f e r e n t s t o c k s have d i f f e r e n t c r i t i c a l s i z e s as e v i d e n c e d by comparison between the Premier and Domestic s t r a i n s ; c o n s e q u e n t l y , the Pennask f i s h may a l l have 37 been w e l l below the c r i t i c a l s i z e f o r t h a t s t o c k . From th e s e d a t a t h e r e i s no way of knowing f o r c e r t a i n . I t would appear, however, t h a t the c r i t i c a l s i z e was not s m a l l e r than 5.0g f o r t h i s s t o c k and s i n c e p r e c o c i o u s males a r e p r e s e n t i n the a n n u a l escapements and may weigh o n l y 200g at t h a t t i m e , i t i s a p p a rent t h a t the c r i t i c a l s i z e f o r Pennask f i s h i s a t l e a s t not as h i g h as f o r the Domestic s t r a i n . W h i l e a r e l a t i o n s h i p between s i z e and development c l e a r l y e x i s t s , i t was not p o s s i b l e i n t h e s e e x p e r i m e n t s t o s e p a r a t e the e f f e c t s of g e n e t i c and s i z e i n f l u e n c e s w i t h i n a g i v e n s t o c k . For example, i t i s p o s s i b l e t h a t the age of f i r s t spawning i s i n h e r i t e d independent of growth r a t e , as suggested by M o l l e r e t a l . (1976) and Naevdal et a l . (1978), but t h a t i n n a t u r e c o n d i t i o n s which s e l e c t f o r e a r l y m a t u r a t i o n c o u l d , i n most i n s t a n c e s , a l s o s e l e c t f o r f a s t e r growth. At f i r s t g l a n c e , i t a ppears as i f the concept of a h e r i t a b l e c r i t i c a l s i z e would l i n k the a s s e r t i o n t h a t age a t f i r s t spawning i s under s t r i c t g e n e t i c c o n t r o l w i t h the a p p a r e n t l y c o n f l i c t i n g view t h a t i t i s s i m p l y s i z e r e l a t e d ; , however, f u r t h e r v e r i f i c a t i o n i s r e q u i r e d . To e s t a b l i s h c r i t i c a l s i z e as a h e r i t a b l e t r a i t and not j u s t a m a n i f e s t a t i o n of a s i m u l t a n e o u s s e l e c t i o n f o r e a r l y age a t f i r s t spawning and f a s t growth, an experiment would have t o be d e s i g n e d t o c l a s s i f y f i s h a c c o r d i n g t o t h e i r i n h e r i t e d growth p o t e n t i a l and s u b s e q u e n t l y t o d e t e r m i n e i f the c r i t i c a l s i z e f o r t h e f a s t and slow growing groups was t h e same. The f i n a l q u e s t i o n t o which t h i s s t u d y was a d d r e s s e d was t o i n v e s t i g a t e whether exposure t o a n a t u r a l p h o t o p e r i o d d u r i n g 38 t h e time window when the t e s t i s began t o d e v e l o p was e s s e n t i a l or whether o t h e r mechanisms c o n t r o l l e d the i n i t i a t i o n of t e s t i s development. S i n c e the f r e q u e n c y of p r e c o c i o u s males was not s i g n i f i c a n t l y d i f f e r e n t between t r e a t m e n t and c o n t r o l groups, i t can be s a f e l y c o n c l u d e d t h a t f o r rainbow t r o u t the i n i t i a t i o n of t e s t i s development i s independent of the p h o t o p e r i o d c o n d i t i o n s a p p l i e d i n t h i s e x p e r i m e n t . T h i s p r o b a b l y p r e c l u d e s the u s e f u l n e s s of p h o t o p e r i o d m a n i p u l a t i o n as an a p p r o p r i a t e method f o r c o n t r o l l i n g the i n c i d e n c e of s e x u a l p r e c o c i o u s n e s s i n h a t c h e r y r e a r e d f i s h and u n d e r l i n e s t h e c o n s i d e r a b l e s i g n i f i c a n c e of the i n t e r n a l c o n t r o l l i n g f a c t o r s whether they be growth r a t e , body s i z e or some o t h e r i n h e r i t e d mechanism which i n f l u e n c e the age a t f i r s t spawning. The r e s u l t s p r e s e n t e d have a l s o c o n f i r m e d the a s s e r t i o n of deVlaming (1974) t h a t f o r s a l m o n i d s the i n i t i a t i o n of gonadal development was independent of e n v i r o n m e n t a l f a c t o r s . S i n c e i t i s not p h o t o p e r i o d which i s c o n t r o l l i n g the onset of gonad m a t u r a t i o n , we a r e l e f t w i t h s e v e r a l o t h e r p l a u s i b l e e x p l a n a t i o n s . C l e a r l y , the r e l a t i o n s h i p between body s i z e and the onset of p r e c o c i o u s development would i n d i c a t e t h a t r e a c h i n g a p h y s i o l o g i c a l age i s mandatory b e f o r e t e s t i s development. The c r i t i c a l p h y s i o l o g i c a l age of an i n d i v i d u a l f i s h which would c o r r e s p o n d t o the pubescent y e a r s of humans c o u l d q u i t e c o n c e i v a b l y be h e r i t a b l e . F u r t h e r m o r e , the i n i t i a t i o n of sper m a t o g e n e s i s appears t o r e q u i r e the f u n c t i o n of the p i t u i t a r y g l a n d (Dodd, 1972). T h i s i s c o n f i r m e d by Crim e t a l . (1975) who found t h a t f o r a v a r i e t y of s a l m o n i d s the 39 p i t u i t a r y was n e c e s s a r y f o r the t r a n s f o r m a t i o n of spermatogonia i n t o p r i m a r y s p e r m a t o c y t e s . T h e r e f o r e , g o n a d o t r o p i n a c t i v i t y would appear t o be the key which u n l o c k s the i n h i b i t o r s of t e s t e s m a t u r a t i o n . S i n c e g o n a d o t r o p i n r e l e a s e from t h e p i t u i t a r y i s under the d i r e c t c o n t r o l of the hypothalamus (Donaldson, 1973), i t i s r e a s o n a b l e t o b e l i e v e t h a t the r e q u i r e d a t t a i n m e n t of a p h y s i o l o g i c a l age i s a s s o c i a t e d w i t h the m a t u r a t i o n , t o a f u n c t i o n a l c o n d i t i o n , of the h y p o t h a l a m i c -p i t u i t a r y c o n t r o l mechanism f o r g o n a d o t r o p i n r e l e a s e . T h e r e f o r e , I c o n c l u d e t h a t the age a t f i r s t m a t u r a t i o n i n rainbow t r o u t i s , i n p a r t , a f u n c t i o n of the time a t which the h y p o t h a l a m i c - p i t u i t a r y a x i s matures to the p o i n t t h a t g o n a d o t r o p i n i s r e l e a s e d and t h a t t h i s a t t a i n m e n t of a c e r t a i n t h r e s h o l d a t an e a r l y age i s o f t e n a s s o c i a t e d w i t h a r a p i d growth r a t e p r i o r t o t e s t i s development. However, t h i s o n l y e x p l a i n s the b e g i n n i n g of the o b s e r v e d time window, a l t h o u g h t h e r e a r e good reasons from a b i o e n e r g e t i c a l p r o s p e c t i v e why an i n d i v i d u a l upon r e a c h i n g the r e q u i r e d p h y s i o l o g i c a l age s h o u l d not s t a r t t e s t i s development i n November or even l a t e r . The r e s u l t s of t h i s study c l e a r l y show t h a t f i s h o n l y s t a r t t o d e v e l o p a t one time of the year and t h e r e i s presumably some i n t e r n a l rhythm which d e f i n e s the time p e r i o d . That q u e s t i o n l e n d s i t s e l f t o f u r t h e r i n v e s t i g a t i o n . I t would appear, t h e r e f o r e , t h a t the h a t c h e r y manager or commercial f i s h farmer may w e l l be a b l e t o reduce the i n c i d e n c e of p r e c o c i o u s s e x u a l development of males by a t l e a s t two 40 s e p a r a t e methods. F i r s t l y , he may depend upon the a s s o c i a t i v e , i f not c a u s a l , r e l a t i o n s h i p between body s i z e d u r i n g the time window and r e s t r i c t growth t o m i n i m i z e the s i z e of h i s f i s h . For the commercial farm, t h i s w i l l c l e a r l y r e s u l t i n added c o s t s and a lower p r o d u c t i o n c a p a b i l i t y , and f o r the f i s h e r y manager i t may r e s u l t i n lower s u r v i v a l s f o r s t o c k e d f i s h . A l t e r n a t i v e l y , he may s e l e c t i v e l y breed f o r l a t e m a t u r i n g f i s h e i t h e r i n a s s o c i a t i o n w i t h or independent from concern f o r t h e i r c a p a c i t y f o r growth. In any event, i t i s d e s i r a b l e t h a t i t be c l e a r l y e s t a b l i s h e d whether the a s s o c i a t i o n between r a p i d growth or l a r g e body s i z e and e a r l y m a t u r a t i o n as observed i n t h e s e e x p e r i m e n t s i s s t r i c t l y a s s o c i a t i v e or a l s o c a u s a l . 41 LITERATURE CITED A l l i s o n , L.N. 1951. Delay of spawning of e a s t e r n brook t r o u t by means of a r t i f i c a l l y p r o l o n g e d l i g h t i n t e r v a l s . P r o g . F i s h . C u l t . , 13:111-116. Aim, G. 1959. C o n n e c t i o n s between m a t u r i t y , s i z e and age i n f i s h e s . I n s t . Freshwat. Res. D r o t t n i n g h o l m , 40:5-145. B i l t o n , H.T. 1971. A h y p o t h e s i s of a l t e r a t i o n of age of r e t u r n i n s u c c e s s i v e g e n e r a t i o n s of Skeena run sockeye. J . F i s h . Res. Bd. Canada, 28:513-516. Bonham K. and L.R. Donaldson. 1972. Sex r a t i o s and r e t a r d a t i o n of g onadal development i n c h r o n i c a l l y g a m m a - i r r a d i a t e d c h i n o o k salmon s m o l t s . T r a n s . Am. F i s h . S o c , 101:428-434. B r e t t , J.R.; J . E . _ S h e l b o u r n ; C T . Shoop. 1969. Growth r a t e and body c o m p o s i t i o n of f i n g e r l i n g sockeye salmon, i n r e l a t i o n t o temperature and r a t i o n s i z e . J . F i s h . Res. Bd. Canada, 26:2363-2393. Campb e l l , R.N. 1971. The growth of brown t r o u t , Salmo t r u t t a L., i n n o r t h e r n S c o t t i s h l o c h s w i t h s p e c i a l r e f e r e n c e t o the improvement of f i s h e r i e s . J . F i s h . B i o l . 3:1-28. Corson, B.W. 1955. Four y e a r s p r o g r e s s i n the use of a r t i f i c a l l y c o n t r o l l e d l i g h t t o induce e a r l y spawning of brook t r o u t . P r og. F i s h . C u l t . , 17:99-102. Cr i m , L.W., E.G. Watts; D.M. Evans. 1975. The plasma g o n a d o t r o p i n p r o f i l e d u r i n g s e x u a l m a t u r a t i o n i n a v a r i e t y of s a l m o n i d f i s h e s . Gen. Comp. E n d o c r i n o l . , 27:62-70. Dodd, J.M. 1972. The e n d o c r i n e r e g u l a t i o n of gametogenesis and gonad m a t u r a t i o n i n f i s h e s . Gen. Comp. E n d o c r i n o l . S u p p l . , 3:675-687. 42 Donaldson, E.M. 1973. R e p r o d u c t i v e e n d o c r i n o l o g y of f i s h e s . Amer. Z o o l . 13:909-927. Donovan, B.T. and J . J . van der W e r f f t e n Bosch. 1965. P h y s i o l o g y of P u b e r t y . I n : 'Monographs of the p h y s i o l o g i c a l s o c i e t y ' (No. 15), eds. H. B a n c r o f t , H. Dawson, W.D.M. Paton. F l a i n , M. 1970. P r e c o c i o u s male q u i n n a t salmon (Oncorchynchus  tshawytcha) i n New Zealand. New Zealand J . Mar. Freshw. Res., 4:217-222. Funk, J.D. and E.M. Donaldson. 1972. I n d u c t i o n of p r e c o c i o u s s e x u a l m a t u r i t y i n male p i n k salmon. Can. J . Z o o l . , 50:1413-1419. Gardner, M.L.G. 1976. A review of f a c t o r s which may i n f l u e n c e the sea-age and m a t u r a t i o n of A t l a n t i c salmon (Salmo s a l a r ) . J . F i s h . B i o l . 9:289-327. Hanson, J.A. and R.H. W i c k w i r e . 1967. F e c u n d i t y and age a t m a t u r i t y of l a k e t r o u t i n Lake Tahoe. C a l i f . F i s h & Game, 53:154-164. H a r r i n g t o n , R.W. 1959. P h o t o p e r i o d i u m i n f i s h e s . In ' P h o t o p e r i o d i s m and r e l a t e d phenomena i n p l a n t s and a n i m a l s ' , Ed. R. Withrow. Amer. Ass o c . Adv. S c i e n c e Pub. No. 55. Washington, D.C. H a s k e l l , D.C. 1948. G r a p h i c a l method of p r e s e n t i n g d ata on the growth of t r o u t . P r o g . F i s h . C u l t . 10(2):59-61. Hazard, T.P. & R.E. Eddy. 1950. M o d i f i c a t i o n of the s e x u a l c y c l e i n the brook t r o u t ( S a l v e l i n u s f o n t i n a l i s ) by c o n t r o l of l i g h t . T r a n s . Am. F i s h . S o c , 80:158-162. Henderson, N.E. 1963. I n f l u e n c e of l i g h t and temperature on the r e p r o d u c t i v e c y c l e of the e a s t e r n brook t r o u t ( S a l v e l i n u s  f o n t i n a l i s ) . J . F i s h . Res. Bd. Canada, 20:859-897. H i r o s e , K. & E.M. Donaldson. 1972. B i o l o g i c a l study on o v u l a t i o n i_n v i t r o of F i s h - I I I . The i n d u c t i o n of i n v i t r o o v u l a t i o n of O r y z i a s l a t i p e s o o c y t e s u s i n g salmon p i t u i t a r y g o n a d o t r o p i n . B u l l . J a p . S o c S c i . F i s h . , 38-97-100. 43 Hoar, W.S. 1969. R e p r o d u c t i o n . I n : F i s h P h y s i o l o g y pp. 1-72, V o l . 3, Eds. W.S. Hoar and D.J. R a n d a l l . Academic P r e s s . N.Y. and London. l i e s , T.D. 1974. The t a c t i c s and s t r a t e g y of growth i n f i s h e s . In "Sea F i s h e r i e s R e s e a r c h " . Eds. F.R. Harden-Jones, pp. 331-345. E l e k S c i e n c e s , London. Iwama, G.K. and A.F. T a u t z . 1981. A s i m p l e growth model f o r s a l m o n i d s i n h a t c h e r i e s . Trans. Am. F i s h . Soc. (In p r e s s ) . J o n e s , J.W. & J.H. O r t o n . 1940. The p a e d o g e n e t i c male c y c l e i n Salmo s a l a r L. P r o c . Roy. Soc. Lond. S e r i e s B. B i o l . S c i . , 128:485-499. K a t o , T. 1975. The r e l a t i o n between the growth and r e p r o d u c t i v e c h a r a c t e r i s t i c s of rainbow t r o u t (Salmo g a i r d n e r i ) . B u l l . F r e s h w a t r . F i s h . Res. Lab. Tokyo, 25:83-99. MacKinnon, C.N. & E.M. Donaldson. 1976. E n v i r o n m e n t a l l y i nduced p r e c o c i o u s s e x u a l development i n the male p i n k salmon. J . F i s h . Res. Bd. Canada, 33:2602-2605. M a r u s h i g e , K. & G.H. D i x o n . 1969. Developmental changes i n chromosal c o m p o s i t i o n t e m p l a t e a c t i v i t y d u r i n g s p ermatogenesis i n t r o u t t e s t e s . Develop. B i o l . , 19:397-414. McFadden, J.T. 1965. Some e f f e c t s of environment on egg p r o d u c t i o n i n brown t r o u t . L i m n o l . Oceanogr. 10:88-95. M o l l e r , D.; G. N a e v d a l ; M. Holm; R. L e r o y . 1976. V a r i a t i o n i n growth r a t e and age a t s e x u a l m a t u r i t y i n rainbow t r o u t . FAO Tech. Rept. FIR. AQ/Conf. 1976. E. 61. N a e v d a l , G.; M. Holm; 0. I n g e b r i g s t e n ; D. M o l l e r . 1978. V a r i a t i o n i n age a t f i r s t spawning i n A t l a n t i c salmon (Salmo s a l a r ) . J . F i s h . Res. Bd. Canada, 35:145-147. 44 Nomura, M. 1963. S t u d i e s on r e p r o d u c t i o n i n rainbow t r o u t w i t h s p e c i a l r e f e r e n c e t o e g g - t a k i n g . 5. Development of gonads and s i z e of f i s h spawned f i r s t l y . B u l l . J a p . Soc. S c i . F i s h . , 29:976-984. Oota, I . ; K. Yamamoto; K. Takano; T. S a k a g u c h i . 1965. S t u d i e s on the m a t u r i n g p r o c e s s i n rainbow t r o u t (Salmo  g a i r d n e r i ) . 2. M a t u r a t i o n of the t e s t i s of a 1-year o l d f i s h . B u l l . J a p . Soc. S c i . F i s h . , 31:597-605. O d e l , W.D. and R.S. S w e r d l o f f . 1972. Rol e of the gonads i n s e x u a l m a t u r a t i o n . I n : ' C o n t r o l of the onset of p u b e r t y ' pp 313-333, Eds. M.M. Grumbach, G.D. Grave, F.E. Mayer. W i l e y and Sons, N.Y. P i c k f o r d , G.E. & J.W. A t z . 1957. P h y s i o l o g y of p i t u i t a r y g l a n d of f i s h e s . New York Z o o l . Soc. New York. R o b e r t s o n , O.H. 1958. A c c e l e r a t e d development of t e s t i s a f t e r u n i l a t e r a l gonadectomy w i t h o b s e r v a t i o n s on normal t e s t i s of rainbow t r o u t . U.S. F i s h & W i l d l i f e S e r . F i s h . B u l l . , 127:9-30. S c h a e f f e r , W.M. & P.F. E l s o n . 1975. The a d a p t i v e s i g n i f i c a n c e of v a r i a t i o n s i n l i f e h i s t o r y among l o c a l p o p u l a t i o n s of A t l a n t i c salmon i n N o r t h A m e r i c a . E c o l o g y , 56:577-590. Schwassman, H.O. 1971. B i o l o g i c a l Rhythms. I n : ' F i s h P h y s i o l o g y ' , p. 371-428, v o l . 6, Eds. W.S. Hoar, D.J. R a n d a l l , Academic P r e s s . N.Y. and London. S t e a r n s , S.C. 1976. L i f e h i s t o r y t a c t i c s : a r e v i e w of the i d e a s . Q u a r t . Rev. B i o l . 51(1):3-47. Simpson, T.H. 1976. E n d o c r i n e a s p e c t s of s a l m o n i d c u l t u r e . P r o c . Roy. Soc. E d i n . ( B ) , 75:241-252. T i t a r e v , Ye. F. 1975. A c c e l e r a t i o n of m a t u r a t i o n i n rainbow t r o u t (Salmo g a i r d n e r i ) under the i n f l u e n c e of i n c r e a s e d water t e m p e r a t u r e . J . I c h t h y o l . , 15:507-509. deVlaming, V.H. 1972. E n v i r o n m e n t a l c o n t r o l of t e l e o s t r e p r o d u c t i v e c y c l e s : a b r i e f r e v i e w . J . F i s h . B i o l . , 4:131-140. deVlaming, V.H. 1974. E n v i r o n m e n t a l and e n d o c r i n e c o n t r o l of t e l e o s t r e p r o d u c t i o n . In " C o n t r o l of sex i n f i s h e s " , Ed C.B. Schre c k . E x t . D i v . , V i r g i n i a P o l y t e c h n i c I n s t . , S t a t e U n i v . B l a c k s b u r g , Va. Wagner, H.H. 1974. P h o t o p e r i o d and temperature r e g u l a t i o n of s m o l t i n g i n s t e e l h e a d t r o u t (Salmo g a i r d n e r i ) . Can. J . Z o o l . , 52:219-234. 

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}]}"
                            data-media="{[{embed.selectedMedia}]}"
                            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.831.1-0095442/manifest

Comment

Related Items