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Prey specialization by individual trout living in a stream and ponds: some effects of feeding history… Bryan, James Ernest 1971

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11207 PREY SPECIALIZATION BY INDIVIDUAL TROUT LIVING IN A STREAM AND PONDS; SOME EFFECTS OF FEEDING HISTORY AND PARENTAL STOCK ON FOOD CHOICE by JAMES' ERNEST BRYAN B . S c , U n i v e r s i t y of Minnesota, r 1966 A Thesis Submitted i n P a r t i a l F u l f i l m e n t of the Requirements f o r the Degree of Doctor of Philosophy In the Department of Zoology ¥e accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA DECEMBER 1971 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by h i s representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia Vancouver 8, Canada Date CWj&nJS*v % i i Chairman: P r o f e s s o r P. A. L a r k i n PREY SPECIALIZATION BY INDIVIDUAL TROUT LIVING IN A STREAM AND PONDS; SOME EFFECTS OF FEEDING HISTORY AND PARENTAL STOCK ON FOOD CHOICE ABSTRACT This study had two purposes: to determine whether i n d i v -i d u a l t r o u t l i v i n g i n the same area s e l e c t d i f f e r e n t kinds of food, and to f i n d out why. Analyses of stomach contents showed that the kinds of prey eaten by t r o u t were seldom d i s -t r i b u t e d at random among the i n d i v i d u a l s . Repeated obser v a t i o n of food eaten by i n d i v i d u a l s i n a stream and ponds showed t h a t prey types were eaten i n p r o p o r t i o n s which were c h a r a c t e r i s t i c f o r an i n d i v i d u a l . Three t r o u t species were s t u d i e d : 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 ( M i t c h i l l ) ; c u t t h r o a t t r o u t , Salmo c l a r k i Richardson; and rainbow t r o u t , Salmo g a i r d n e r i Richardson. F u r t h e r analyses were performed to d e s c r i b e the nature of food s p e c i a l i z a t i o n i n t r o u t . In the stream, i n d i v i d u a l s with e i t h e r p o s i t i v e or negative s p e c i a l i z a t i o n measures ate sim-i l a r assortments of food. However, those with negative measures had eaten s l i g h t l y more of prey types a v a i l a b l e f o r short time periods than had those with p o s i t i v e measures. Although the degree of s p e c i a l i z a t i o n was higher during s h o r t e r i n t e r v a l s , the data suggested that some s p e c i a l i z a t i o n p e r s i s t e d f o r h a l f a year. There were no s t r i k i n g c o r r e l a t i o n s between degree of s p e c i a l i z a t i o n and other i n d i v i d u a l p r o p e r -t i e s such a s : s i z e , growth r a t e , weight of f o o d , number of k i n d s of f o o d , p r e v i o u s s p e c i a l i z a t i o n , or area of r e c a p t u r e . A f i e l d experiment was conducted u s i n g l a b o r a t o r y - r e a r e d rainbow t r o u t h e l d i n s m a l l ponds. The food of each t r o u t was sampled r e p e a t e d l y . In a n a l y s i s of v a r i a n c e , i n t e r a c t i o n among the i n d i v i d u a l s and k i n d s o f prey eaten showed t h a t food s p e c i a l i z a t i o n o c c u r r e d . Prey abundance was constant d u r i n g the experiment . F e e d i n g h i s t o r y and p a r e n t a l s t o c k were m a n i p u l a t e d to determine whether they could i n f l u e n c e food s e l e c t i o n i n young rainbow t r o u t . A f t e r 9 t r a i n i n g meals of one f o o d , t r o u t s e l e c t e d t h a t f o o d , the f a m i l i a r one, when g i v e n a c h o i c e between i t and a n o v e l f o o d . (Most choice s i t u a t i o n s used h i g h and equal d e n s i t i e s of unconcealed f o o d s ) . S e l e c -t i o n of the f a m i l i a r f o o d o c c u r r e d w i t h s e v e r a l k i n d s of n o n - l i v i n g f o o d . T r o u t t r a i n e d on l i v e p r e y , however, d i d not always s e l e c t the f a m i l i a r one when b o t h prey were a l i v e , a l t h o u g h they d i d when b o t h prey were dead. Some c h a r a c t e r i s t i c s of the t r a i n i n g e f f e c t were i n v e s t -i g a t e d . As they became s a t i a t e d , t r o u t consumed r e l a t i v e l y more o f the n o v e l f o o d . D u r a t i o n of f o o d d e p r i v a t i o n b e f o r e a c h o i c e t e s t d i d not change the degree of s e l e c t i o n f o r the f a m i l i a r f o o d . In a d d i t i o n to e a t i n g more of the f a m i l i a r f o o d , t r o u t s t r u c k but r e j e c t e d r e l a t i v e l y more of the n o v e l f o o d . I n d i v i d u a l t r o u t t r a i n e d on two foods ate them i n p r o p o r t i o n s which were c h a r a c t e r i s t i c f o r an i v i n d i v i d u a l . A f t e r t h e y had l e a r n e d t o s e l e c t one f o o d , t r o u t "were g i v e n f u r t h e r t r a i n i n g on one of t h e f o l l o w i n g : t h e f a m i l i a r f o o d , a n o v e l f o o d , or b o t h . F u r t h e r t r a i n i n g on t h e f a m i l i a r f o o d d i d n o t change the p r o p o r t i o n s e l e c t e d . T r o u t t r a i n e d on one f o o d f o r 12 meals and t h e n on a second f o o d f o r 12 meals s e l e c t e d t h e s e c o n d f o o d when g i v e n a c h o i c e . Yhen the i n i t i a l t r a i n i n g was f o l l o w e d by c o n t i n u o u s f e e d i n g o f b o t h f a m i l i a r and n o v e l f o o d , t r o u t c o n t i n u e d t o s e l e c t t h e f a m i l i a r f o o d f o r 14 t o 23 m e a l s . A l l r e s u l t s s u g g e s t e d t h a t e f f e c t s o f s u c h f e e d i n g h i s t o r y would not g r e a t l y i n f l u e n c e f o o d s e l e c t i o n i n n a t u r a l s i t u a t i o n s . P r o g e n y of p a r e n t a l s t o c k s were t e s t e d t o d e t e r m i n e whether p a r e n t a l f o o d c a n i n f l u e n c e f o o d s e l e c t e d by o f f s p r i n g . Eggs f r o m t r o u t w h i c h ate d i f f e r e n t k i n d s o f f o o d were h a t c h e d i n the l a b o r a t o r y . F o r t h e i r f i r s t meal, t r o u t were g i v e n c h o i c e s of t h e k i n d s of f o o d e a t e n by t h e p a r e n t a l s t o c k s . I n t h r e e m a i n e x p e r i m e n t s , t h e young t r o u t d i d n o t s e l e c t t h e t y p e of f o o d commonly e a t e n by t h e i r p a r e n t s . V TABLE OF CONTENTS Page TITLE PAGE i ABSTRACT i i TABLE OF CONTENTS v LIST OF TABLES v i i i LIST OF FIGURES x i i ACKNOWLEDGMENT x i v INTRODUCTION 1 PRET SPECIALIZATION BY INDIVIDUALS OF TROUT POPULATIONS 2 ABSTRACT 2 INTRODUCTION 4 MATERIALS AND METHODS 6 The study areas and animals 6 Trout c o l l e c t i o n 8 Food sampling 9 RESULTS 11 Method of a n a l y s i s 15 Food of i n d i v i d u a l s recaptured from a stream and pond 1 7 Method of small pond experiment 29 Res u l t s of small pond experiment 34 DISCUSSION 41 BIBLIOGRAPHY 48 APPENDIX 50 FEEDING HI STORY r, PARENTAL STOCK, AND FOOD SELECTION IN RAINBO¥ TROUT 54 ABSTRACT 54 INTRODUCTION 56 MATERIALS AND METHODS 60 The experimental animals 60 Laboratory c o n d i t i o n s 60 T r a i n i n g and t e s t i n g foods 61 T r a i n i n g procedure 64 T e s t i n g procedure 65 A n a l y s i s 66 RESULTS PART I 68 E f f e c t s of f e e d i n g h i s t o r y on food s e l e c t i o n 68 T r a i n i n g on dead t u b i f e x and b r i n e shrimp 68 T r a i n i n g b i a s w i t h l i v e food 75 T r a i n i n g biases with other foods 78 S a t i a t i o n and degree of t r a i n i n g b i a s 78 Food d e p r i v a t i o n and degree of t r a i n i n g b i a s 80 P r o p o r t i o n of t r a i n i n g and novel food r e j e c t e d 82 Food s e l e c t i o n by i n d i v i d u a l s w i t h i n treatments 84 Fur t h e r t r a i n i n g on the o r i g i n a l food 86 Fur t h e r t r a i n i n g on a novel food 88 Further t r a i n i n g on both the o r i g i n a l and novel foods 88 DISCUSSION OF PART I 93 v i i RESULTS PART I I 105 E f f e c t s of p a r e n t a l stock on food s e l e c t i o n 105 S e l e c t i o n of daphnia, mayfly l a r v a e , and hatchery food 105 S e l e c t i o n of hatchery food and l i v e plankton 106 Consumption of l i v i n g and n o n - l i v i n g planktdn 110 Other d i f f e r e n c e s between domestic and w i l d stocks 114 DISCUSSION OP PART II 115 BIBLIOGRAPHY 122 LIST OF TABLES PREY SPECIALIZATION BY INDIVIDUALS OF TROUT POPULATIONS T a b l e Pag I Food eaten by rainbow t r o u t and mountain w h i t e -f i s h caught i n a g i l l net i n F u l t o n R i v e r . The t r o u t were caught at the same time on three s u c -c e s s i v e n i g h t s , whereas the w h i t e f i s h were a l l caught w i t h i n an hour on the same day . 1 I I Food and l e n g t h of 4 rainbow t r o u t c a p t u r e d i n M a r s h a l l Creek ( S e c t i o n 2B; September 4, 1968; 1800-1900 P S T ) . 1 I I I F o o d , l e n g t h , and sex of 7 rainbow t r o u t c a p t u r e d i n the F i s h i n g Pond (March 2, 1969; 1100-1300 P S T ) . 1 IV Mean v a l u e s of f o o d s i m i l a r i t y (r c o n v e r t e d to z) w i t h i n and between i n d i v i d u a l t r o u t . The maximum i n t e r v a l between capture and r e c a p t u r e was t h r e e weeks (mean 11.4 d a y s ) . 1 V C o r r e l a t i o n between f o o d s i m i l a r i t y (z w i t h i n ) , f o o d s p e c i a l i z a t i o n (z w i t h i n - z between) and other c h a r a c t e r i s t i c s of i n d i v i d u a l t r o u t which were r e c a p t u r e d . A l l comparisons are b l o c k e d by s p e c i e s and by the time i n t e r v a l between capture and r e c a p t u r e (1-20, 21-50, and 51-200 d a y s ) . Data on weight of f o o d eaten are f o r rainbow t r o u t o n l y , hence the c o r r e l a t i o n c o e f f i c i e n t s have 175 d f . The other data are f o r a l l three s p e c i e s and have 238 d f . 2 VI The f r e q u e n c y of capture of i n d i v i d u a l t r o u t w i t h f o o d i n a l l s e c t i o n s of M a r s h a l l Creek between September 4, 1968 and October 9, 1969. The data are based on r e c o r d s f o r a l l s p e c i e s and a l l i n d i v i d u a l s w i t h f o o d . V I I Comparison of June and August r e p l i c a t i o n s of the s m a l l pond experiment . V I I I A n a l y s e s o f v a r i a n c e of weights of prey eaten i n the s m a l l pond exper iment . IX S t a t i s t i c a l l y s i g n i f i c a n t e f f e c t s i n the s m a l l pond exper iment . The symbols are d e f i n e d i n T a b l e V I I I . i x FEEDING HISTORY, PARENTAL STOCK, AND FOOD SELECTION IN RAINBO¥ TROUT T a b l e Page I Comparison of experiments on t r a i n i n g b i a s i n d i f f e r e n t a n i m a l s . The words " y e s " and " n o " answer q u e s t i o n s i n d i c a t e d . P l u s or minus i n d i c a t e s whether any experiments d i d or d i d not use the m a t e r i a l i n d i c a t e d . 57 I I S i z e d i s t r i b u t i o n of t u b i f e x and b r i n e shrimp used i n Experiment 7. Each d i s t r i b u t i o n i s based on three counts of about 500 p i e c e s of f o o d . 63 IIIo D e s c r i p t i o n of a l l experiments u s i n g dead t u b i -fex and b r i n e shrimp as t r a i n i n g f o o d s . Except f o r those of Experiment 6, a l l t r o u t had eaten o n l y t h e i r t r a i n i n g f o o d ( s ) b e f o r e the t e s t meals . 69 IV Food s e l e c t e d by t r o u t g i v e n a c h o i c e between dead t u b i f e x and b r i n e shrimp a f t e r t r a i n i n g w i t h the same f o o d ( s ) f o r a t l e a s t 9 meals . The data are the t o t a l number of p i e c e s eaten by a l l f i s h i n t h e i r f i r s t t e s t meal . Dashes i n d i c a t e o m i s -s i o n of a t reatment from an experiment . 71 V • Food chosen by the t r o u t of Experiments 2 and 3 which were t r a i n e d s i n g l y and i n groups of t h r e e w i t h i n p l a s t i c c o n t a i n e r s . These t r o u t were t e s t e d d u r i n g t r a i n i n g , and the schedule of t r a i n -i n g and t e s t i n g meals was: 3 , 1 ; 6 ,2 ; 12 ,2 ; 24 ,2 . The data are t o t a l number of pieces eaten by a l l i n d i v i d u a l s i n a l l t e s t s . 72 VI E f f e c t of t r a i n i n g on p r o p o r t i o n of t u b i f e x ( a r c s i n e per cent f o r each i n d i v i d u a l ) eaten i n the f i r s t meal a f t e r t r a i n i n g . The data are from Experiments 1 to 7, but o n l y the t u b i f e x , b r i n e shr imp, and h a t c h e r y food t reatments are i n c l u d e d i n the a n a l y s i s . 74 VII„ Number of t u b i f e x and b r i n e shrimp eaten by a l l t r o u t t r a i n e d on l i v e t u b i f e x f o r 75 meals then t e s t e d w i t h l i v e and dead f o o d . The t e s t s w i t h l i v e food used 50 t u b i f e x and 50 b r i n e s h r i m p , whereas those w i t h dead f o o d used the u s u a l p r o -cedure . 77 X V I I I Food eaten by t r o u t (8/treatment) t r a i n e d on l i v e d a p h n i a , l i v e m a y f l y l a r v a e , or h a t c h e r y food and t e s t e d w i t h 30 dead daphnia and 20 dead mayf ly l a r v a e . 79 IX E f f e c t of s a t i a t i o n on t r a i n i n g b i a s . The data are means f o r response of i n d i v i d u a l s c o n v e r t e d to s i n g l e d e v i a t e s as d e s c r i b e d i n t e x t . P o s i t i v e v a l u e s i n d i c a t e s e l e c t i o n f o r t u b i f e x and n e g a t i v e v a l u e s , s e l e c t i o n f o r b r i n e s h r i m p . 81 X E f f e c t of t r a i n i n g on k i n d of food eaten and k i n d r e j e c t e d by t r o u t . Pood of each f i s h was c o n v e r t -ed to a s i n g l e d e v i a t e as i n Table IX . P o s i t i v e v a l u e s i n d i c a t e s e l e c t i o n f o r t u b i f e x and n e g a -t i v e v a l u e s , s e l e c t i o n f o r b r i n e s h r i m p . 83 XI P r o p o r t i o n of t u b i f e x and b r i n e shrimp ( a r c s i n e per cent t u b i f e x ) eaten by i n d i v i d u a l t r o u t t r a i n e d on both foods f o r 75 meals b e f o r e the t e s t meals . The e n t i r e schedule of unobserved and observed meals was: 7 5 , 3 ; 4 , 2 ; 4 , 2 . C o n s e c u t i v e t e s t s were used as r e p l i c a t e s . 85 XII Numbers of t u b i f e x and b r i n e shrimp eaten by t r o u t a f t e r t r a i n i n g on two foods i n s u c c e s s i o n (12 meals of each f o o d ) . The data are t o t a l s f o r the 12 t r o u t i n each treatment,. 89 X I I I P e r s i s t e n c e of t r a i n i n g b i a s when t r o u t are a l l o w e d to eat b o t h t e s t foods a f t e r the t r a i n i n g p e r i o d . The data are t o t a l food of 12 i n d i v i d u a l s per t r e a t -ment, and the same i n d i v i d u a l s were observed on s u c c e s s i v e meals , w i t h i n exper iments . 92 X l V a Number of daphnia and m a y f l y l a r v a e eaten by n a i v e t r o u t of t h r e e p a r e n t a l s t o c k s when o f f e r e d : d a p h n i a , m a y f l y l a r v a e , and hatchery f o o d . The r e l a t i v e d e n s i t y of daphnia to m a y f l y l a r v a e was always 3 to 2 , b u t a b -s o l u t e d e n s i t i e s d i f f e r e d as d e s c r i b e d i n the t e x t . 107 b Number of t r o u t d e s c r i b e d above which ate (+) or d i d not eat (-) h a t c h e r y f o o d , or d i d not eat any food (0) . 108 c The mean f o r k l e n g t h (mm, w i t h SE i n parentheses ) of each s t o c k d e s c r i b e d above a f t e r p r e s e r v a t i o n i n 10$ f o r m a l i n . 109 XV Food of n a i v e domestic and w i l d s t o c k s (20 of each) o f f e r e d l i v e p l a n k t o n and h a t c h e r y f o o d . 111 XVIa E f f e c t of s t o c k , n a t u r e o f f o o d , and s o c i a l s i t u a t i o n on l o g number o f p l a n k t o n i c o r g a n -isms e a t e n by n a i v e t r o u t . The d o m e s t i c and w i l d s t o c k (40 o f each) were a l l o c a t e d t o two t r e a t m e n t s : f e e d i n g on l i v e o r dead p l a n k t o n ; f e e d i n g s i n g l y or i n a gr o u p of f i v e . b Mean a r i t h m e t i c number o f org a n i s m s e a t e n p e r i n d i v i d u a l . The a v e r a g e s t a n d a r d e r r o r was 3.840, n = 10. x i i LIST OF FIGURES PREY SPECIALIZATION BY INDIVIDUALS OF TROUT POPULATIONS F i g u r e Page 1 The p o r t i o n of M a r s h a l l Creek s t u d i e d and the F i s h i n g Pond. D o t t e d l i n e s i n d i c a t e s u b s e c t i o n b o u n d a r i e s . 7 2 Food eaten by t r o u t w i t h p o s i t i v e or n e g a t i v e s p e c i a l i z a t i o n measures (z^ - ) compared w i t h f o o d eaten by those not r e c a p t u r e d w i t h i n 21 d a y s . The data are f o r a l l three t r o u t s p e c i e s . 20 3 D i f f e r e n c e i n mean food s i m i l a r i t y ( w i t h i n -between) f o r a l l t h r e e t r o u t s p e c i e s over d i f f e r e n t i n t e r v a l s of c a p t u r e . V e r t i c a l bars i n d i c a t e s t a n d a r d e r r o r s . The number of w i t h i n comparisons i s w r i t t e n below each p o i n t . 22 4 Food eaten by a l l c u t t h r o a t t r o u t and rainbow t r o u t c a p t u r e d i n s u b s e c t i o n 2B of M a r s h a l l Creek at d i f f e r e n t seasons d u r i n g 1968 and 1969. 24 5 Food eaten by c u t t h r o a t and rainbow t r o u t c a p t u r e d i n d i f f e r e n t s u b s e c t i o n s of M a r s h a l l Creek between A p r i l 10 and October 9, 1969. 27 6 I n s i d e dimensions (cm) of the ponds used i n the s m a l l pond exper iment . Each pond was p a r t i t i o n e d i n t o three s e c t i o n s w i t h p a s s a g e -ways (pw) between s e c t i o n s . 30 7 Food eaten by i n d i v i d u a l s i n ponds where low or h i g h s p e c i a l i z a t i o n was apparent d u r i n g the f i r s t week (June r e p l i c a t i o n ) . 37 8 Food eaten by i n d i v i d u a l s i n ponds where low or h i g h s p e c i a l i z a t i o n was apparent d u r i n g the f i r s t week (August r e p l i c a t i o n ) . 38 Appendix 1 Length d i s t r i b u t i o n (n = 406) of a l l t r o u t s p e c i e s i n M a r s h a l l C r e e k . The data i n c l u d e l e n g t h s of a l l f i s h whether c a p t u r e d or r e c a p t u r e d . 51 x i i i A p p e n d i x 2 D i s t r i b u t i o n o f s p e c i a l i z a t i o n measures (n=248) f o r a l l t h r e e t r o u t s p e c i e s i n M a r s h a l l C r e e k . The maximum time i n t e r v a l between c a p t u r e and r e c a p t u r e was 250 d a y s . A p p e n d i x 3 S e a s o n a l d i s t r i b u t i o n o f s p e c i a l i z a t i o n measures f o r a l l t h r e e t r o u t s p e c i e s i n M a r s h a l l C r e e k . The maximum t i m e i n t e r v a l between c a p t u r e and r e c a p t u r e was 250 d a y s . FEEDING HISTORY, PARENTAL STOCK, AND FOOD SELECTION IN RAINBOY TROUT F i g u r e Page 1 P r o p o r t i o n o f t u b i f e x e a t e n by t r o u t o f f e r e d b o t h t u b i f e x and b r i n e s h r i m p a f t e r t r a i n i n g on d i f f e r e n t f o o d ( s ) . S t r i p e d b a r s i n d i c a t e s t a n d a r d e r r o r s ; numbers above t h e a b s c i s s a a r e numbers o f t r o u t w h i c h a t e any f o o d d u r i n g a c h o i c e t e s t . 70 2 E f f e c t o f t r a i n i n g d u r a t i o n on t h e amount o f t r a i n i n g f o o d e a t e n . P o i n t s i n d i c a t e means and l i n e s s t a n d a r d e r r o r s . (The a r c s i n e o f 50$ i s 45.) 8 ? 3 P r o p o r t i o n o f t u b i f e x e a t e n by a l l i n d i v i d u a l s a f t e r two s u c c e s s i v e t r a i n i n g p e r i o d s . The p e r i o d s l a s t e d 12 m e a l s ; a f t e r t h e s e c o n d p e r i o d , t h e t r o u t were g i v e n a c h o i c e of t u b i -f e x ( T) and b r i n e s h r i m p ( S ) . H r e p r e s e n t s h a t c h e r y f o o d . 90 ACKNOWLEDGMENT I am e s p e c i a l l y g r a t e f u l to D r . P. A . L a r k i n , my r e -s e a r c h s u p e r v i s o r , f o r s u g g e s t i o n s and i n s p i r a t i o n . M r . N. E . G i l b e r t p r o v i d e d many h e l p f u l s u g g e s t i o n s about s t a t -i s t i c a l a n a l y s i s . The a n a l y s e s of f i e l d data were developed i n the course of d i s c u s s i o n s among the three of u s . I w i s h to thank the f o l l o w i n g persons who a s s i s t e d with f i e l d or l a b o r a t o r y work at d i f f e r e n t t i m e s : M r . R. Babb, Mr . ¥ . R. B l a c k , Mr . M. B. Lambert , D r . D. L . Kramer, M r . A . D. Maurer , D r . J . S. S t impson, Mr. A . P . T a u t z , and Mr. B. Wong. I am g r a t e f u l to M r . S. W. Borden and M r s . D. L a u r i e n t e - f o r a d v i c e on and h e l p w i t h programming. M i s s S. Senkow p r o v i d e d domestic t r o u t f o r Experiment 1 2 . Mr . G. S. Jamieson, D r . G. G. E . Scudder , and M i s s K. M. S t u a r t k i n d l y helped i d e n t i f y some i n s e c t l a r v a e . D r . C. S. H o l l i n g , D r . M. H . Keenleyside , D r . J . D. M c P h a i l , and D r . T . G. N o r t h c o t e o f f e r e d s u g g e s t i o n s about the r e s e a r c h and c r i t i c i z e d the t h e s i s . F i n a n c i a l a s s i s t a n c e was p r o v i d e d by the N a t i o n a l Research C o u n c i l of Canada, the H . R. M a c M i l l a n F o u n d a t i o n , and the Department o f Zoology of the U n i v e r s i t y of B r i t i s h C o l u m b i a . The B r i t i s h Columbia F i s h and W i l d l i f e Branch p r o v i d e d some f a c i l i t i e s and e x p e r i m e n t a l a n i m a l s . I am g r a t e f u l to many p e r s o n n e l of the B r a n c h , e s p e c i a l l y Mr . F . H . M a r t i n and Mr . R. A . H . Sparrow, f o r i n f o r m a t i o n about t r o u t c u l t u r e . 1 INTRODUCTION T h i s t h e s i s d e s c r i b e s v a r i o u s o b s e r v a t i o n s and e x p e r i -ments a l l c o n c e r n i n g i n d i v i d u a l d i f f e r e n c e s i n k i n d of f o o d e a t e n by t r o u t . The t h e s i s has two major s e c t i o n s . The f i r s t d e s c r i b e s f o o d e a t e n by i n d i v i d u a l s i n t h e f i e l d , and t h e second d e s c r i b e s t h e development of i n d i v i d u a l d i f f e r -ences i n t h e l a b o r a t o r y . E a c h s e c t i o n i s a c o m p l e t e u n i t , c o n t a i n i n g more s p e c i f i c i n t r o d u c t o r y r e m arks. B o t h f i e l d and l a b o r a t o r y r e s e a r c h were s t i m u l a t e d by t h e o b s e r v a t i o n t h a t i n d i v i d u a l t r o u t c a p t u r e d i n t h e f i e l d had e a t e n f o o d t y p e s i n d i f f e r e n t p r o p o r t i o n s . S u b s e q u e n t f i e l d work was u n d e r t a k e n t o d e m o n s t r a t e t h a t s u c h h e t e r o -geneous f o o d d i s t r i b u t i o n s r e s u l t e d b e c a u s e i n d i v i d u a l s s p e c i a l i z e d ( r e p e a t e d l y s o u g h t out d i f f e r e n t p r e y ) . ¥hile making t h e s e f i e l d o b s e r v a t i o n s , I was a l s o t r y i n g t o d e t e r -mine what can make i n d i v i d u a l s s p e c i a l i z e i n the l a b o r a t o r y . A l t h o u g h t h e two were contemporaneous, t h e f i e l d r e s e a r c h i s a u s e f u l p r e f a c e t o t h e l a b o r a t o r y r e s e a r c h . 2 PREY SPECIALIZATION BY INDIVIDUALS OF TROUT POPULATIONS ABSTRACT A n a l y s e s o f stomach c o n t e n t s showed t h a t t h e k i n d s o f p r e y e a t e n by t r o u t were seldom d i s t r i b u t e d a t random among t h e i n d i v i d u a l s . R e p e a t e d o b s e r v a t i o n o f f o o d e a t e n by i n d i v -i d u a l s i n a stream and ponds showed t h a t p r e y t y p e s were e a t e n i n p r o p o r t i o n s w h i c h were c h a r a c t e r i s t i c f o r an i n d i v i d u a l . T h r e e t r o u t s p e c i e s were s t u d i e d : b r o o k t r o u t , S a l v e l i n u s  f o n t i n a l i s ( M i t c h i l l ) ; c u t t h r o a t t r o u t , Salmo c l a r k i R i c h a r d -son; and r a i n b o w t r o u t , Salmo g a i r d n e r i R i c h a r d s o n . F u r t h e r a n a l y s e s were p e r f o r m e d t o d e s c r i b e t h e n a t u r e o f f o o d s p e c i a l i z a t i o n i n t r o u t . I n the s t r e a m , i n d i v i d u a l s w i t h e i t h e r p o s i t i v e or n e g a t i v e s p e c i a l i z a t i o n measures a t e s i m i l a r a s s o r t m e n t s o f f o o d . However, t h o s e w i t h n e g a t i v e measures had e a t e n s l i g h t l y more of p r e y t y p e s a v a i l a b l e f o r s h o r t t i m e p e r i o d s t h a n had t h o s e w i t h p o s i t i v e measures. A l t h o u g h t h e d e g r e e of s p e c i a l i z a t i o n was h i g h e r d u r i n g s h o r t e r i n t e r v a l s , t h e d a t a s u g g e s t e d t h a t some s p e c i a l i z a t i o n p e r s i s t e d f o r h a l f a y e a r . T h e r e were no s t r i k i n g c o r r e l a t i o n s between d e g r e e o f s p e c i a l i z a t i o n and o t h e r i n d i v i d u a l p r o p e r -t i e s s u c h a s : s i z e , growth r a t e , w e i g h t o f f o o d , number o f k i n d s o f f o o d , p r e v i o u s s p e c i a l i z a t i o n , or a r e a o f r e c a p t u r e . I n a d d i t i o n t o t h e o b s e r v a t i o n s on t r o u t i n r e l a t i v e l y u n d i s t u r b e d h a b i t a t s , a f i e l d e x p e r i m e n t was c o n d u c t e d u s i n g l a b o r a t o r y - r e a r e d r a i n b o w t r o u t h e l d i n s m a l l ponds. The f o o d o f each t r o u t was sampled r e p e a t e d l y . I n a n a l y s i s o f v a r i a n c e , i n t e r a c t i o n among t h e i n d i v i d u a l s and k i n d s o f p r e y e a t e n 3 showed t h a t food s p e c i a l i z a t i o n o c c u r r e d . Both the a b s o l u t e and r e l a t i v e abundances of p o t e n t i a l prey were constant d u r i n g the experiment . 4 INTRODUCTION ¥h i l e e x a m i n i n g stomach c o n t e n t s of t r o u t and w h i t e f i s h c a p t u r e d a t t h e same t i m e and p l a c e , I n o t i c e d t h a t t h e k i n d s o f f o o d were n o t d i s t r i b u t e d r a n d o m l y among t h e stomachs. Some i n d i v i d u a l s had e a t e n m a i n l y one k i n d o f p r e y , some a n o t h e r , and some b o t h k i n d s . T h i s o b s e r v a t i o n s u g g e s t e d t h e h y p o t h e s i s t h a t i n d i v i d u a l s w i t h i n a p o p u l a t i o n ( a n i m a l s l i v i n g i n t h e same a r e a ) s p e c i a l i z e on p a r t i c u l a r k i n d s o f p r e y ; and t h e r e f o r e , t h a t s u b s e q u e n t f o o d o f t h e same i n d i v -i d u a l s would be s i m i l a r . The n u l l h y p o t h e s i s i s t h a t i n d i v -i d u a l s a r e n o t c o n s i s t e n t about t h e k i n d o f p r e y c a p t u r e d on d i f f e r e n t o c c a s i o n s . These h y p o t h e s e s were t e s t e d w i t h f i e l d o b s e r v a t i o n s and a f i e l d e x p e r i m e n t . H e t e r o g e n e i t y i n f o o d e a t e n by i n d i v i d u a l s o f a p o p u l a -t i o n has been r e p o r t e d f o r o t h e r p r e d a t o r s : salmon, c a r p , s u n f i s h , s a l a m a n d e r s , t i t m i c e , and g u l l s ( A l l e n , 1941; I v l e v , 1961; Reed, MS 1971; N e i s h , MS 1970; T i n b e r g e n , 1960; and H a r r i s , 1965). However, d a t a were p r e s e n t e d f o r o n l y s u n f i s h and t i t m i c e . T i n b e r g e n (1960) p r e s e n t s d a t a on f o o d c a p t u r e d by g r e a t and b l u e t i t s s u g g e s t i n g t h a t i n d i v i d u a l s s p e c i a l i z e d on p a r t i c u l a r p r e y s p e c i e s . U n f o r t u n a t e l y , o b s e r v a t i o n s were p r e s e n t e d f o r o n l y some of t h e i n d i v i d u a l s s t u d i e d t h o s e t h a t had caught p r e y d i f f e r i n g f r o m p r e y o f o t h e r i n d i v i d u a l s so i t i s n o t p o s s i b l e t o d e t e r m i n e whether s p e c i a l i z a t i o n i s t y p i c a l i n t i t s . N e i s h (MS 1970) f o u n d t h a t most o f t h e s a l a m a n d e r s c a p t u r e d i n d i f f e r e n t s u b h a b i t a t s o f a l a k e 5 r e t u r n e d to those s u b h a b i t a t s to f e e d when e n c l o s e d by pens i n the l a k e . The s u b h a b i t a t s d i f f e r e d i n p r o p o r t i o n of p o t e n -t i a l prey types as d i d food of salamanders f e e d i n g i n d i f f e r -ent s u b h a b i t a t s ( I . C . N e i s h , p e r s o n a l communicat ion) . As w i t h the t i t s , the salamanders s t u d i e d were not an u n b i a s s e d sample of the p o p u l a t i o n . 6 MATERIALS AND METHODS The S t u d y A r e a s and A n i m a l s Most o f t h e t r o u t sampled i n " n a t u r a l " h a b i t a t s were c o l l e c t e d f r o m M a r s h a l l C r e e k , a s m a l l s p r i n g - f e d s t r e a m n e a r A b b o t s f o r d , B r i t i s h C o l u m b i a (49 122 SE, F i g u r e 1 ) . P a r t of t h e c r e e k ( S u b s e c t i o n s 1A and B) was on t h e grounds of t h e F r a s e r V a l l e y T r o u t H a t c h e r y (B. C. F i s h and W i l d l i f e B r a n c h ) . Water i n t h e s e s e c t i o n s f l o w e d f r o m t r o u g h s u s e d t o r e a r t r o u t , and t h e y had a m a i n l y c l a y b o t t o m w i t h some g r a v e l b u t l i t t l e a q u a t i c v e g e t a t i o n . The o t h e r s e c t i o n s had bottoms o f m a i n l y sand or g r a v e l w i t h w a t e r c r e s s a l o n g t h e m a r g i n . The d e p t h r a n g e d f r o m a b o u t 25 cm i n r i f f l e s t o 90 cm i n p o o l s , and r a t e s o f f l o w a r e g i v e n i n F i g u r e 1. The w a t e r t e m p e r a t u r e r a n g e d s e a s o n a l l y f r o m about 9 t o 11° C. Deformed f i n s w i t h c u r v e d r a y s i n d i c a t e d t h a t about h a l f t h e t r o u t s t u d i e d had been r e a r e d i n t h e h a t c h e r y . I n a d d i -t i o n , a bout one t h i r d o f t h e ra i n b o w t r o u t had m o r p h o l o g i c a l c h a r a c t e r i s t i c s o f a d o m e s t i c s t o c k . The l e n g t h ( f o r k l e n g t h ) d i s t r i b u t i o n s o f t h e t h r e e s p e c i e s were s i m i l a r ( A p p e n d i x F i g u r e 1; mean 182 mm and range 109 t o 362), a l t h o u g h t h e mean o f ra i n b o w t r o u t was s l i g h t l y g r e a t e r . S e v e r a l s p e c i e s o f f i s h were c o l l e c t e d f r o m M a r s h a l l C r e e k , b u t o n l y some were r e s i d e n t s p e c i e s . I n a d d i t i o n t o t h e t h r e e t r o u t s p e c i e s , C-ast er os t e u s a c u l e a t u s , C o t t u s  a s p e r , l a r v a l L a mpetra p l a n e r i , and young Oncorhynchus  k i s u t c h were p r e s e n t f o r most o f t h e y e a r . A d u l t L. p l a n e r i ? The p o r t i o n of M a r s h a l l Creek s t u d i e d and the F i s h i n g Pond. D o t t e d l i n e s i n d i c a t e s u b s e c t i o n b o u n d a r i e s . 7 8 0. k i s u t c h , , 0. k e t a , and Catostomus m a c r o c h e i l u s were o b s e r v e d i n t h e c r e e k d u r i n g t h e i r r e s p e c t i v e spawning s e a s o n s . A S a l v e l i n u s malma and a P t y o c h e i l u s o r e g o n e n s e were c o l l e c t e d i n t h e s t r e a m . F o r t h r e e weeks, I o b s e r v e d t h e f o o d e a t e n by r a i n b o w t r o u t l i v i n g i n t h e F i s h i n g Pond ( F i g u r e 1 ) . L o c a t e d on h a t c h e r y g r o u n d s , t h e pond had been dug a t l e a s t 6 y e a r s b e f o r e t h e s t u d y . The t r o u t i n i t had t h e morphology o f a d o m e s t i c s t o c k . The pond had a mud and c l a y s u b s t r a t u m p a r t l y c o v e r e d by a l g a e ; some o f i t s s u r f a c e was c o v e r e d by a mat o f a l g a e and v a s c u l a r p l a n t s ; i t had a f a i r l y u n i f o r m d e p t h o f 1 m. T r o u t C o l l e c t i o n I n t h e s t r e a m , f i s h were caught w i t h e l e c t r o s h o c k i n g a p p a r a t u s ( G e o r a t o r C o r p . , Manassas, Va., U. S . A.; g e n e r -a t o r model 31-002, 230 v d-c, 2.2 amp). The s h o c k i n g p r o -c e d u r e was s i m i l a r t o t h a t of H a s k e l l and Z i l l i o x ( 1 9 4 0 ) . C a r r y i n g t h e anode, I waded u p s t r e a m , n e t t e d the ..stunned f i s h w i t h a d i p net, and handed t h e n e t t o an a s s i s t a n t . The method p r e s u m a b l y had t h e u s u a l b i a s s e s and c a p t u r e e f f i c -i e n c y ( E l s o n , 1950; A l a b a s t e r and H a r t l e y , 1962). The c o n d u c t i v i t y o f water i n M a r s h a l l C r e e k was 148 micromhos/cm a t 2 0.3° C. (T. G. N o r t h c o t e , p e r s o n a l c o m m u n i c a t i o n ) . A l t h o u g h 3.2$ d i d n o t r e c o v e r f r o m s h o c k i n g , most t r o u t d i e d when l a r g e numbers were s t u n n e d s i m u l t a n e o u s l y and p a r t i c -u l a r l y when many i n d i v i d u a l s had p h y s i c a l s i g n s of d i s e a s e . W i t h i n an hour of c a p t u r e , a l l t r o u t were c a r r i e d to my l a b -o r a t o r y , a d j a c e n t to the t r o u t h a t c h e r y , where t h e i r water was c o o l e d and a e r a t e d . Not a l l s u b s e c t i o n s of the stream were sampled throughout the course of s t u d y . S u b s e c t i o n 2B was sampled from September 4, 1968 to October 9, 1969. I n order to capture more t r o u t , I began sampling s u b s e c t i o n s 3A and B on March 29, 1969, and s u b s e c t i o n s 1A and B on A p r i l 10. I sampled s u b s e c t i o n 2A o c c a s i o n a l l y to o b t a i n t r o u t f o r exper iments . In p a r e n t h e s e s , the s u b s e c t i o n s are l i s t e d i n order of d e c r e a s i n g t r o u t c a p -t u r e (1A, 33.5%; 2B, 26.8%; 1B, 21.3%; 3A, 9.4%; 2A, 5.5%; and 3B, 3.5%). Except f o r the f i r s t week of s a m p l i n g , a l l t r o u t were c o l l e c t e d a t midday (1100 to 1330 P a c i f i c S tandard T i m e ) . S e v e r a l d i f f e r e n t i n t e r v a l s of capture were used but the u s u a l and s a t i s f a c t o r y i n t e r v a l was b i w e e k l y . W i t h s h o r t e r i n t e r v a l the percentage of r e c a p t u r e d t r o u t decreased and the p e r c e n t a g of t r o u t w i t h o u t f o o d was g r e a t e r ; w i t h longer i n t e r v a l s , the changes i n k i n d of prey eaten seemed g r e a t e r . In the F i s h i n g Pond the t r o u t were c o l l e c t e d w i t h g i l l n e t s . A f t e r the t h i r d s u c c e s s i v e week of c a p t u r e , 3 of 7 t r o u t i n the F i s h i n g Pond d i e d , a p p a r e n t l y from i n j u r i e s i n -f l i c t e d by the n e t s , so sampling was d i s c o n t i n u e d . Food Sampling Most f o o d samples were o b t a i n e d by f l u s h i n g the stomach 10 of each t r o u t w i t h water . The apparatus and procedure f o r stomach f l u s h i n g were s i m i l a r to those d e s c r i b e d by Seaburg (1957). Food samples were p r e s e r v e d i n 10$ f o r m a l i n . L a t e r , the prey i n each sample were i d e n t i f i e d , counted , and weighed (to 0.1 gm, wet w e i g h t ) . V i n d e l l and N o r r i s (1969) suggest the time when the f o o d i n samples c o u l d have been ea ten . N e a r l y a l l f o o d eaten 6 to 8 hr b e f o r e capture would have been p r e s e n t as would 80-20$ eaten 9-24 hr b e f o r e c a p t u r e . Of a l l stomachs, 81.6$ c o n t a i n e d f o o d . Before stomach f l u s h i n g , each t r o u t was a n e s t h e t i z e d w i t h 2 - p h e n o x y - e t h a n o l (0.5 m l / l ) . T h i s c o n c e n t r a t i o n p r o -duced n a r c o s i s i n 1-2 minutes and r e c o v e r y i n 5-8 ( 8 - 1 2 ° C ) . Other p r o p e r t i e s of the a n e s t h e t i c are i n d i c a t e d by B e l l (1964). A f t e r b e i n g a n e s t h e t i z e d , each f i s h was measured ( w i t h i n 3 mm) and marked w i t h a s m a l l green p l a s t i c t a g ( 3 x 10 x 0.5 mm). The tags were a t t a c h e d w i t h monofilament through the d o r s a l musculature j u s t a n t e r i o r to the d o r s a l f i n . Of t r o u t which s u r v i v e d s h o c k i n g , about 3.5$ d i e d a f t e r a n e s t h e s i a , stomach f l u s h i n g , and t a g g i n g . In the l a b o r a t o r y , 16 i n d i v i d u a l s which s u r v i v e d s h o c k i n g and h a n d l i n g l i v e d f o r a t l e a s t a month. A l l t r o u t were r e t u r n e d to t h e i r p l a c e of capture w i t h i n 3 h r . The method of a n a l y s i s and methods used i n the f i e l d experiment are p r e s e n t e d w i t h the r e s u l t s . 11 RESULTS The food d i s t r i b u t i o n among i n d i v i d u a l t r o u t caught at n e a r l y the same time and p l a c e was u s u a l l y heterogeneous — the stomachs of d i f f e r e n t i n d i v i d u a l s c o n t a i n i n g d i f f e r e n t p r o -p o r t i o n s of k i n d s of prey eaten by a l l i n d i v i d u a l s . T a b l e I p r e s e n t s stomach content data from f i s h c o l l e c t e d near a spawn-i n g channel where h i g h d e n s i t i e s of salmon f r y and i n s e c t l a r v a e were p r e s e n t f o r s e v e r a l weeks. The w h i t e f i s h data were i n -c l u d e d because a l l had been captured at n e a r l y the same t i m e . I f a g r e a t e r number of t r o u t had been captured s i m u l t a n e o u s l y , I would expect t h e i r f o o d d i s t r i b u t i o n to resemble t h a t of the w h i t e f i s h . The i n d i v i d u a l t r o u t were s i m i l a r i n l e n g t h (23 to 36 cm) as were the w h i t e f i s h (24 to 30 cm). These two sets of data were chosen as examples because they meet the u s u a l r e -quirements f o r a n a l y s i s of c o n t i n g e n c y t a b l e s (most expected v a l u e s ^> 5 ). H e t e r o g e n e i t y i n f o o d of i n d i v i d u a l t r o u t was common, a l t h o u g h i t was not always a d v i s a b l e to t e s t food samples f o r h e t e r o g e n i t y u s i n g s tandard s t a t i s t i c a l methods. T a b l e s II and I I I p r e s e n t the food of i n d i v i d u a l s captured on the f i r s t days M a r s h a l l Creek and the F i s h i n g Pond were sampled. The f o o d of these i n d i v i d u a l s was heterogeneous . However, s e v e r a l f o o d c a t e g o r i e s w i t h o n l y one food i tem were omit ted f o r s t a t i s t i c a l r e a s o n s , and the a n a l y s i s s t i l l r e l i e d upon the robustness d e s c r i b e d by Lewont in and F e l s e n s t e i n (1965); not a l l s t a t i s t i c i a n s agree about the r o b u s t n e s s . Even w i t h -out s t a t i s t i c a l a n a l y s i s , the data suggest t h a t a l l i n d i v i d u a l s 12 Table I . Food eaten by rainbow t r o u t and mountain w h i t e f i s h caught i n a g i l l net i n F u l t o n R i v e r . The t r o u t were caught at the same time on three s u c c e s s i v e n i g h t s , whereas the w h i t e f i s h were a l l caught w i t h -i n an hour on the same day. F i s h number Number of food items I n s e c t l a r v a e Salmon f r y Rainbow 1 101 1 T r o u t 2 17 16 3 0 61 4 27 19 5 41 0 6 200 0 7 100 0 X 2 = 436 df = 6 p < .001 Mountain 1 1 3 W h i t e f i s h 2 10 0 3 7 0 4 7 0 5 0 20 6 0 8 7 6 32 8 0 27 9 10 4 10 40 0 X 2 = 140 df = 9 p < .001 13 T a b l e I I . Food and l e n g t h of 4 rainbow t r o u t captured i n M a r s h a l l Creek ( S e c t i o n 2B; September 4, 1968; 1800-1900 P S T ) . The data are numbers of items ea ten . K i n d of Food Organism T r o u t 1 119 mm T r o u t 2 186 mm T r o u t 3 163 mm T r o u t 4 137 mm D i p t e r a pupa 0 0 39 2 Chironomid l a r v a 10 9 75 2 O l i g o c h a e t e 5 0 0 0 M a y f l y n a i a d 2 1 22 0 S u r f a c e organism 0 0 16 1 ^ 2 = 64.2 df = 12 p < 0.001 T a b l e I I I . F o o d , l e n g t h , and sex of 7 rainbow t r o u t captured i n the F i s h i n g Pond (March 2, 1969; 1100-1300 P S T ) . The data are numbers of items ea ten . K i n d of Food T r o u t T r o u t T r o u t T r o u t T r o u t Trout T r o u t Organism 1 2 3 4 5 6 7 S ? 2 2 3 2 9 440 mm 381 mm 458 mm 443 mm 563 mm 413 mm 490 mm C o r i x i d 0 2 5 0 0 3 0 M a y f l y n a i a d 0 3 11 2 0 1 0 D a m s e l f l y n a i a d 0 5 3 0 1 5 0 Isopod 0 1 2 0 0 21 0 Amphipod 0 0 5 0 1 3 0 C a d d i s f l y l a r v a 0 0 3 0 0 5 0 Salamander 4 0 0 0 0 0 0 O l i g o c h a e t e 0 6 33 56 0 42 0 = 335.3 df = 35 P < 0.001 14 had not eaten a l l foods i n the same p r o p o r t i o n . The o b s e r v a t i o n s t h a t food was not d i s t r i b u t e d randomly among i n d i v i d u a l t r o u t suggested t h a t some i n d i v i d u a l s r e p e a t e d l y seek out p a r t i c u l a r k i n d s of p r e y . In order to t e s t t h i s h y p o t h e s i s , I r e c a p t u r e d i n d i v i d u a l s from the two h a b i t a t s d e s c r i b e d p r e v i o u s l y . The food eaten by r e c a p t u r e d i n d i v i d u a l s at two d i f f e r e n t t imes was compared w i t h food of other i n d i v i d u a l s to determine whether food of captured i n -d i v i d u a l s was more s i m i l a r than expected by chance. The a n a l y s i s i s d e s c r i b e d i n the f o l l o w i n g s e c t i o n . 15 Method o f A n a l y s i s The s i m i l a r i t y o f f o o d samples of r e c a p t u r e d i n d i v i d u a l s •was compared w i t h s i m i l a r i t y of samples f r o m o t h e r i n d i v i d -u a l s . The a n a l y s i s was c o m p l i c a t e d by n o n o r t h o g o n a l d a t a r e s u l t i n g f r o m i n f r e q u e n t r e c a p t u r e . C o n s e q u e n t l y s t a n d a r d s t a t i s t i c s were i n a d e q u a t e , and s p e c i a l a n a l y s i s was d e v e l -oped t o make t h e a p p r o p r i a t e c o m p a r i s o n s . The p r e y i t e m s were c l a s s i f i e d i n t o c a t e g o r i e s a c c o r d i n g t o major taxonomic groups ( F i g u r e s 2, 4, 5 ) . The c a t e g o r y o f t e r r e s t r i a l o r g a n i s m i n c l u d e d a d u l t a q u a t i c i n s e c t s and any o t h e r o r g a n i s m t h o u g h t t o have been c a p t u r e d on t h e s u r f a c e o f t h e w a t e r . Most a n a l y s e s u s e d the number o f o r g a n i s m s i n ea c h f o o d c a t e g o r y . Two k i n d s o f f o o d , h a t c h e r y f o o d and p l a n t m a t e r i a l , c o u l d n o t be c o u n t e d , so t h e s e f o o d s were a s s i g n e d t h e v a l u e 1. The measure o f f o o d s i m i l a r i t y a d o p t e d was r , t h e product-moment c o r r e l a t i o n c o e f f i c i e n t . E a c h v a l u e o f r was c o n v e r t e d t o a n o r m a l d e v i a t e z. F o r m u l a e and c h a r a c t e r -i s t i c s o f t h e s e s t a t i s t i c s a r e p r e s e n t e d i n many t e x t b o o k s ( e g . S t e e l and T o r r i e , 1960). I m o d i f i e d t h e v a l u e s o f r under two c i r c u m s t a n c e s . To a v o i d d i v i s i o n by z e r o , any r c a l c u l a t e d t o be + 1.0 was ch a n g e d t o + 0.99. I f one and t h e same k i n d o f f o o d was p r e s e n t i n two f o o d samples, r was a s s i g n e d t h e v a l u e + 0.99. A l t h o u g h r i s n o r m a l l y u n d e f i n e d i n s u c h c i r c u m s t a n c e s , s u c h samples were as s i m i l a r as p o s s i b l e . O t h e r c o m p a r i s o n s f o r w h i c h r was u n d e f i n e d ( b e c a u s e one t r o u t had e a t e n no f o o d or had e a t e n e q u a l 16 q u a n t i t i e s o f a l l c a t e g o r i e s ) were o m i t t e d f r o m a n a l y s i s . The t o t a l o f s i m i l a r i t y measures f o r t h e r e c a p t u r e d i n -d i v i d u a l s , w i t h i n c o m p a r i s o n s , was o b t a i n e d by summing s i m -i l a r i t y measures f o r p a i r s o f f o o d samples e a t e n by each r e c a p t u r e d i n d i v i d u a l . T h r e e r e s t r i c t i o n s were p l a c e d upon t h e p o s s i b l e p a i r s o f samples i n c l u d e d among w i t h i n c o m p a r i -sons. A s i m i l a r i t y measure was c a l c u l a t e d o n l y when t h e i n d i v i d u a l had been c a p t u r e d and r e c a p t u r e d d u r i n g a s p e c i f i e d t i m e i n t e r v a l , w h i c h was n o t t h e same i n a l l a n a l y s e s . F o r the s t r e a m h a b i t a t , measures were o n l y computed when t h e i n d i v i d u a l had been caught i n s i m i l a r s u b s e c t i o n s each t i m e ( S u b s e c t i on 1A or 1B b o t h t i m e s , or any c o m b i n a t i o n o f : 2A, 2B, 3A, and 3B). I n t h e main a n a l y s i s ( T a b l e I V ) , a t h i r d r e s t r i c t i o n was p l a c e d upon measures f o r i n d i v i d u a l s w h i c h had been c a p t u r e d s e v e r a l t i m e s . F o r s u c h i n d i v i d u a l s , f o o d samples were compared o n l y i f b o t h had n o t been u s e d i n a p r e v i o u s c o m p a r i s o n . T h i s r e s t r i c t i o n e l i m i n a t e d d u p l i c a t e use o f i n f o r m a t i o n , making the c o m p a r i s o n s a p p r o x i m a t e l y o r t h o g o n a l . The t o t a l o f s i m i l a r i t y measures f o r d i f f e r e n t i n d i v -i d u a l s , between c o m p a r i s o n s , was o b t a i n e d by co m p a r i n g t h e f o o d samples o f each t r o u t u s e d f o r a w i t h i n c o m p a r i s o n w i t h f o o d samples o f s e v e r a l o t h e r i n d i v i d u a l s . I n t h e s t r e a m h a b i t a t , f i v e r e s t r i c t i o n s were p l a c e d on p o s s i b l e between c o m p a r i s o n s . T r o u t had t o be o f t h e same s p e c i e s and l e n g t h ( w i t h i n + 15$), f r o m t h e same s e c t i o n ( 1 , 2, 3; F i g u r e 1 ) , and c a p t u r e d t h e same t i m e s as t h e r e c a p t u r e d i n d i v i d u a l . 17 In the main a n a l y s i s (Table I V ) , the betwe en comparisons were a l s o r e s t r i c t e d to make them a p p r o x i m a t e l y o r t h o g o n a l . Comparisons were made o n l y i f a food sample had not a l r e a d y been used f o r comparison w i t h another i n d i v i d u a l caught the same t i m e s . The two groups of s i m i l a r i t y measures were compared to determine whether the weighted f requency of large v a l u e s was g r e a t e r i n the w i t h i n s than i n the betweens. As the s i m i l a r -i t y measures were n o r m a l l y d i s t r i b u t e d , the d i f f e r e n c e i n c e n t r a l tendency was a n a l y z e d u s i n g an u n p a i r e d t - t e s t . A l -though a t h e o r e t i c a l es t imate was a v a i l a b l e , a l l s tandard e r r o r s were e s t i m a t e d e m p i r i c a l l y . Food of I n d i v i d u a l s Recaptured from a Stream and a Pond T a b l e IV p r e s e n t s r e s u l t s of o b s e r v a t i o n s of t r o u t i n the stream and pond h a b i t a t s . In a l l cases , food samples from the same i n d i v i d u a l s ( w i t h i n comparisons) were more s i m i l a r than food samples from d i f f e r e n t i n d i v i d u a l s (between c o m p a r i s o n s ) . U s i n g data f o r rainbow t r o u t o n l y , the weight of f o o d i n each ca tegory was a n a l y z e d w i t h the same methods, and s i m i l a r r e s u l t s were o b t a i n e d . Because the f o o d of the same i n d i v i d u a l was, on the average , more s i m i l a r than the food of d i f f e r e n t i n d i v i d u a l s , i t f o l l o w s t h a t i n d i v i d u a l s had s p e c i a l i z e d on some of the prey eaten by the e n t i r e p o p -u l a t i o n . The food of the i n d i v i d u a l s was examined to determine Table I V . Mean v a l u e s of food s i m i l a r i t y (r conver ted to z) w i t h i n and between i n d i v i d u a l t r o u t . The maximum i n t e r v a l between capture and r e c a p t u r e was t h r e e weeks (mean 11.4 d a y s ) . H a b i t a t S p e c i e s W i t h i n Comparisons Betwe en Comparisons z - z, w b t v a l u e df P< Mean z w n Mean z, b n Pond Rainbow t r o u t -0 .15 11 -0 .47 48 .31 0.68 59 .3 Stream Rainbow t r o u t 0.82 56 0.45 247 •37 1 .72 301 .05 Stream C u t t h r o a t t r o u t 0.71 20 -0.1 3 50 .84 2.20 68 .025 Stream Brook t r o u t 1 .33 5 0.23 11 1.10 1 .29 14 .2 TOTAL ALL SPECIES 0.71 92 0.08 356 0.63 3.62 446 .001 19 whether t r o u t w i t h h i g h or low f o o d s i m i l a r i t y t e n d e d t o e a t u n u s u a l k i n d s o f f o o d . I n b o t h h a b i t a t s , t h e d i f f e r e n t k i n d s of f o o d were e a t e n by many o f t h e i n d i v i d u a l s , t h o u g h w i t h u n e q u a l f r e q u e n c y . I n t h e pond h a b i t a t , an e x c e p t i o n was t h e t r o u t w h i c h had e a t e n s a l a m a n d e r s ( T a b l e I I I ) ; i t was th e o n l y t r o u t w h i c h had e a t e n them and had done so on each o f t h e t h r e e o b s e r v a t i o n s . ¥ h e n t e s t e d i n t h e l a b o r a t o r y , t h i s i n d i v i d u a l chose t o e a t s a l a m a n d e r s when o f f e r e d s m a l l t r o u t and o t h e r f o o d s i n T a b l e I I I . F i g u r e 2 compares t h e f o o d d i s t r i b u t i o n s f o r i n d i v i d u a l s w i t h p o s i t i v e and n e g a t i v e s p e c i a l i z a t i o n measures. The s p e c i a l i z a t i o n measure i s t h e s i m i l a r i t y measure f o r a r e -c a p t u r e d i n d i v i d u a l ( z w ) minus t h e mean s i m i l a r i t y measure between i n d i v i d u a l s c a p t u r e d a t t h e same t i m e s ( z ^ K The d a t a o f F i g u r e 2 were a n a l y z e d i n T a b l e IV. However, d a t a were o m i t t e d f o r t i m e s when no t r o u t were r e c a p t u r e d . D a t a f o r 9 i n d i v i d u a l s c a p t u r e d s e v e r a l t i m e s were p l a c e d i n b o t h d i s t r i b u t i o n s b e c a u s e one c o m p a r i s o n had a n e g a t i v e measure and t h e o t h e r a p o s i t i v e one. F i g u r e 2 shows t h a t t r o u t i n each o f t h e d i s t r i b u t i o n s r a n k e d t h e f o o d c a t e g o r i e s i n n e a r l y the same o r d e r . T h e r e were minor d i f f e r e n c e s among t h e d i s t r i b u t i o n s w h i c h may have b i o l o g i c a l meaning. The f o o d d i s t r i b u t i o n of t r o u t n o t r e c a p t u r e d was i n t e r m e d i a t e between t h o s e o f t r o u t w i t h p o s i t i v e or n e g a t i v e measures, f o r most f o o d c a t e g o r i e s . Types o f p r e y w h i c h were d r i f t i n g or e m e r g i n g ( d i p t e r a pupa, o s t e i c h t h y e s egg, e p h e m e r o p t e r a n a i a d , and t e r r e s t r i a l PER CENT OF TOTAL FOOD 8 8 6 z • Q "n D D • OTHER DIPTERA P .. I! CHERONDMIDAE L .. 1 llBtflCZDhE £.. I GASTROPOD* 1 TUBrFICIDAE 09TEICHTHYES E I EPHEWEROPTERA L TRICHDPTERA COREXIOAE .. HIRUDINEA .. COLEDPTERA L CLAOQCERA TERREST • ANIMAL PLECOPTERA L . . AMPHIPODA . OTHER DIPTERA L . . COPEPCIDA .. PELECYPODA PLANT MATERIAL . OSTRACODA AO- EARTHWORM DDDNATA L OSTErCHTHYES COLEOPTERA .. 9YRPHIDAE P .. ACARI ESOPDDA TRIQ.AOIDA HATD-ETRY FOOD hiiiiii]!ii:(ii nm tiisniiiinji Ul) ni IfnTtttt fYlfn ii<ii: i • • itsi m B r~ II r~ > 73 TJ II II ro iiiiiiiiiiiiin (Ni N ro CD NE T J • > - \ l-H — 1 < l-H < m m z Z II II CD ffl UL) CD hd I—I S3 O h r j o O O h i 3 o h d C u P p h - > h i CD CD P C u c + CD 4 H -CD CD h b e + O 4 O O O C u C < H - c + CD 03 P £ c + - H -CD CD c + O H -CD a* h i m o • 03 O H -in <! 0 CD 2 O O h j c + y 4 CD CD rjq o P P c t -h j H -c + < C l CD CD 03 C u h J CD < O H - H -c + P & M 0 N P to c + — 1 H -O P <<: 3 03 CD • P 03 C •-a 4 v CD CD 03 C u . — P N p I p 4 N CD O ' OZ 21 a n i m a l ) , were u s u a l l y eaten to a g r e a t e r extent by t r o u t w i t h n e g a t i v e s p e c i a l i z a t i o n measures. Such prey were p r e -sumably v e r y abundant f o r s h o r t p e r i o d s of t i m e . C o n v e r s e l y , k i n d s of food presumably o b t a i n e d by f o r a g i n g ( c h i r o n o m i d l a r v a , g a s t r o p o d a , and o s t e i c h t h y e s ) , were eaten more f r e -q u e n t l y by t r o u t w i t h p o s i t i v e s p e c i a l i z a t i o n measures. A l t h o u g h t h i s g e n e r a l i z a t i o n was not t r u e f o r the chi ronomid l a r v a of F i g u r e 2 , nor when rainbow t r o u t were a n a l y z e d a l o n e , i t was t r u e of both brook and c u t t h r o a t t r o u t . Most o ther d i f f e r e n c e s between t r o u t w i t h p o s i t i v e and n e g a t i v e measures were apparent when food d i s t r i b u t i o n s f o r each s p e c i e s were c o n s i d e r e d a l o n e . The s i m i l a r i t y and s p e c i a l i z a t i o n measures were examined f o r evidence t h a t t h e r e were two types of t r o u t : those t h a t s p e c i a l i z e d and those t h a t d i d n o t . However, the d i s t r i b u t i o n s of the measures were unimodal (Appendix F i g u r e 2 ) , s u g g e s t i n g t h a t there was o n l y one t y p e . Moreover , i n d i v i d u a l s c a p t u r e d s e v e r a l t imes d i d not have measures which were c h a r a c t e r i s t i c -a l l y e i t h e r low or h i g h . The measures were a l s o examined to see whether they were h i g h e r at some seasons than others (Appendix F i g u r e 3 ) ; the d i s t r i b u t i o n s were s i m i l a r i n d i f f e r e n t seasons . Food s i m i l a r i t y over d i f f e r e n t time i n t e r v a l s was exam-i n e d f o r an e f f e c t on degree of s p e c i a l i z a t i o n . F i g u r e 3 p r e s e n t s these data and shows t h a t the degree of s p e c i a l i z a -t i o n was h i g h e r over s h o r t i n t e r v a l s between capture and r e -c a p t u r e . Indeed, the degree of s p e c i a l i z a t i o n seemed to FIGURE 3 . D i f f e r e n c e i n mean food s i m i l a r i t y ( w i t h i n - between) f o r a l l three t r o u t species over d i f f e r e n t i n t e r v a l s of capture. V e r t i c a l bars i n d i c a t e standard e r r o r s . The number of w i t h i n comparisons i s w r i t t e n below each p o i n t . 00 M I N - 0 . 4 200 TIME B E T W E E N C A P T U R E AND R E C A P T U R E (DAYS) to to 23 d e c l i n e (20-30 d a y s ) and t h e n t o i n c r e a s e a g a i n (50-60 d a y s ) . The r e s t r i c t i o n s on t h e c o m p a r i s o n s i n F i g u r e 3 were t h e same as i n T a b l e I V e x c e p t t h a t t h e y were n o t made a p p r o x i m a t e l y o r t h o g o n a l . O r t h o g o n a l c o m p a r i s o n s were n o t made be c a u s e i n f o r m a t i o n would have been d i s c a r d e d and because t h e d a t a were n o t i n t e n d e d for. use w i t h s i g n i f i c a n c e l e v e l s . F i g u r e 3 s u g g e s t s t h a t some r e s i d u a l s p e c i a l i z a t i o n may have o c c u r r e d a t i n t e r v a l s o f 60-250 d a y s . A l o n g d u r a t i o n o f s p e c i a l i z a t i o n was p o s s i b l e b e c a u s e f e e d i n g o p p o r t u n i t i e s seemed s t a b l e . F i g u r e 4 shows t h a t many k i n d s o f p r e y were e a t e n t h r o u g h o u t t h e y e a r , d e s p i t e p o s s i b l e f l u c t u a t i o n s i n r e l a t i v e abundance. V a r i o u s c h a r a c t e r i s t i c s o f t r o u t and t h e i r f o o d samples a r e compared by c o r r e l a t i o n i n T a b l e V. The d a t a were b l o c k e d by time t o make t h e c o m p a r i s o n s more homogeneous, and t h i s a c c o u n t s f o r t h e s l i g h t l y p o s i t i v e c o r r e l a t i o n between r e c a p t u r e i n t e r v a l ' ( v a r i a t e 3) and the s i m i l a r i t y measures ( v a r i a t e s 1 and 2 ) . C o n v e r s i o n of l e n g t h t o l o g a r i t h m s made d i f f e r e n c e s l i n e a r ( P a r k e r and L a r k i n , 1959). A l t h o u g h t h e r e were s t a t i s t i c a l l y s i g n i f i c a n t c o r r e l a t i o n s between t h e f o o d s i m i l a r i t y measures and o t h e r v a r i a t e s , none o f them a c c o u n t e d f o r even 10% o f the v a r i a t i o n i n f o o d s i m i l a r i t y or s p e c i a l i -z a t i o n ( r <C 0 . 1 ) . P e r h a p s t h e most n o t e w o r t h y c o r r e l a t i o n s were t h o s e between t h e s i m i l a r i t y measures ( v a r i a t e s 1 and 2) and b o t h t h e w e i g h t and number o f k i n d s o f f o o d ( v a r i a t e s 4 t o 1 0 ) . The o n l y o t h e r c o r r e l a t i o n s w h i c h seem m e a n i n g f u l a r e t h o s e between t h e number of k i n d s o f f o o d e a t e n ( v a r i a t e s FIGURE 4. 60 4-Food eaten by a l l c u t t h r o a t and rainbow t r o u t captured i n s u b s e c t i o n 2B of M a r s h a l l Creek at d i f f e r e n t seasons d u r i n g 1968 and 1969. SEPT^ 4 - NOV' 17 iN-59) •EL'- 1 - MAR. 1 (N=17) MAR«29 - JUNE 1 CN=15) SEPT-7 - OCT-9 CN=7) E=EGG» L = L A R V A » P=PUPA n 1 1 1 S ! i I S Ihi i H h 3 Ui 6 4 < 2 a. t-8 5 - i 5 U l o < 5 Ul = H — = - + -< CL a a 6 2 d I-I U. KIND CF FOOD to T a b l e V . C o r r e l a t i o n between food s i m i l a r i t y (z w i t h i n ) , food s p e c i a l i z a t i o n (z w i t h i n - z between), and other c h a r a c t e r i s t i c s of i n d i v i d u a l t r o u t which were r e c a p t u r e d . A l l comparisons are b l o c k e d by s p e c i e s and by the time i n t e r v a l between capture and r e c a p t u r e (1-20, 21-50, and 51-200 d a y s ) . Data on weight of food eaten are f o r rainbow t r o u t o n l y , hence the c o r r e l a t i o n c o e f f i c i e n t s have 175 d f . The other data are f o r a l l three s p e c i e s and have 238 d f . VARIATE VN VARIATE NUMBER (VN) 10 1 1 Z w i t h i n 1 ,-808 Z w i t h i n - Z between 2 T2 - T1 3 .028 .018 No. k i n d s f o o d T1 4 .182** .078 - .154 No. k i n d s f o o d T2 5 . 1 64* .101 - .002 .768 m . 765 m No. k i n d s f o o d T1+T2 6 .226** .117 - .102 _ Log (No. k i n d s T1+T2) 7 .281** .160* - .096 .739 r a .731" 1 • 959m (Wt f o o d T 1 ) / l o g L 8 .,176* .143* - .102 .328** .080 .273** .227** (Wt f o o d T 2 ) / l o g L 9 - .039 --.033 - .016 .241** .342** .385** .300** .205** (Kt f o o d T1+T2 ) / l o g L 10 .084 .067 - .075 .365** .277** .426** .341** . 758 m Log (L a t T2) 11 .183** .173* - . 040 .223** .162* .251** .204** .242** D a i l y growth i n L 12 .055 .050 - .028 .187** .170* .233** .227** .088 . 7 9 3 m  .249** .317*^ .195** .184* .010 T1 i s the time when a f i s h was c a p t u r e d . T2 i s the time when a f i s h was r e c a p t u r e d . L i s the l e n g t h (mm) of the f i s h at T1 , T2, or the average at T1 and T2. * and * * i n d i c a t e p r o b a b i l i t i e s (0.05 and 0.01) of f o r t u i t o u s d i f f e r e n c e from z e r o . (The p r o b a b i l i t i e s are not n e c e s s a r i l y a c c u r a t e because not a l l comparisons were o r t h o g o n a l ) , i n d i c a t e s t h a t the two v a r i a t e s b e i n g c o r r e l a t e d are not m a t h e m a t i c a l l y independent . m Ul 26 4 to 7) and both the weight of food ( v a r i a t e s 8 to 10) and growth r a t e ( v a r i a t e 12) . As d e s c r i b e d i n the p r e v i o u s s e c t i o n , the stream h a b i t a t d i f f e r e d between S e c t i o n 1 and downstream sections (2 and 3 ) . Moreover , F i g u r e 5 shows t h a t the food eaten by t r o u t i n d i f f e r e n t s u b s e c t i o n s d i f f e r e d i n r e l a t i v e abundance. As a r e s u l t , one might expect a g r e a t e r degree of food s p e c i a l i -z a t i o n by i n d i v i d u a l s r e c a p t u r e d from the same s u b s e c t i o n than from d i f f e r e n t s u b s e c t i o n s . To t e s t t h i s h y p o t h e s i s , the s p e c i a l i z a t i o n a n a l y s e s were r e p e a t e d . S u r p r i s i n g l y , there was l e s s s p e c i a l i z a t i o n by t r o u t r e c a p t u r e d from the same s u b -s e c t i o n (mean z - z, = 0 .64, SE = 0.225, n = 43) than by v w b ' ' w ' J those r e c a p t u r e d from d i f f e r e n t s u b s e c t i o n s (mean - z^ = 0 .85 , SE = 0.312, n = 3 1 ) . However, t h i s d i f f e r e n c e was ' ' w ' not s t a t i s t i c a l l y s i g n i f i c a n t . S e v e r a l o b s e r v a t i o n s suggested t h a t t r o u t m o r t a l i t y was h i g h or t h a t t r o u t f r e q u e n t l y l e f t the stream study a r e a . T a b l e VI shows t h a t most i n d i v i d u a l s were captured o n l y one t i m e . The t o t a l number of t r o u t of a l l s p e c i e s caught i n a p o r t i o n of stream always decreased w i t h cont inued, s a m p l i n g . T h i s was p a r t i c u l a r l y apparent when samples were c o l l e c t e d f r e q u e n t l y . F o r i n s t a n c e , when S u b s e c t i o n 2B was sampled 5 t imes i n 3 days (September 4-6 , 1968), the number of t r o u t c a p t u r e d each time decreased from 8 to 3; when three s u b -s e c t i o n s (2B, 3A, and 3B) were sampled on a l t e r n a t e days f o r 5 days ( A p r i l 5-13, 1969), the number caught decreased from 15 to 1. The c a t c h of marked t r o u t by a n g l e r s i n d i c a t e d some 27 FIGURE 5. Food eaten by c u t t h r o a t and rainbow t r o u t captured i n d i f f e r e n t s u b s e c t i o n s of M a r s h a l l Creek between A p r i l 10 and October 9, 1969. 40 .. 30.. a a a u. < fe r Y). m TA "I'lN H AREA 1A CN-119) j | AREA IB (N= 7S) I t rB^ [ML 10.. I AREA 2A (N-B) AREA 2B CN=13) AREA 3A (N=17) AREA 3B CN- 2) E=EGG» L-LARVA? P^ RJPA *l " I » I H H—=+-0. J Ul 6 a a T— M »-* U. J . D- 5 U r- U. t M O *-* tO X ° s is a 3 p I 1 s - i S p * * B I i B g 6 B 5 S B ^ J i ^ E B ft - ? f 1 f KINO OF FOOD I B S 6 5 £ ri * 8 8 I LD •< Q. M s 6 I £ B £ 8 s 3 § 28 T a b l e V I . The f r e q u e n c y of capture of i n d i v i d u a l t r o u t w i t h food i n a l l s e c t i o n s of M a r s h a l l Creek between September 4, 1968 and October 9, 1969. The data are based on r e c o r d s f o r a l l s p e c i e s and a l l i n d i -v i d u a l s w i t h f o o d . Maximum I n t e r v a l Number of Times an I n d i v i d u a l was Captured Between Capture and Recapture 1 2 3 4 5 6 21 Days 167 41 12 5 2 73.6$ 18.1$ 5.3$ 2.2$ 0.< 0 250 Days 167 54 16 65.5$ 21.2$ 6.3$ 8 6 4 3.1$ 2 .4$ 1.6$ 29 had l e f t the s tudy a r e a . Of a l l i n d i v i d u a l s ever tagged and r e l e a s e d i n the stream (235), f i s h e r m a n caught about 2.6% w i t h i n the s tudy a r e a , 3.4% l e s s than 1 km away, and 2.6% more t h a n 1 km away. Those c a p t u r e d o u t s i d e the study area were caught b o t h upstream and downstream from i t . F i s h i n g i n t e n s i t y was not u n i f o r m l y d i s t r i b u t e d , p a r t i c u l a r l y as no f i s h i n g was a l l o w e d i n s u b s e c t i o n s on h a t c h e r y grounds where the t r o u t d e n s i t y was g r e a t e s t . Methods of Smal l Pond E x p e r i m e n t . T h i s experiment was d e s i g n e d to t e s t the same h y p o t h e s i s as o b s e r v a t i o n s i n "the stream and pond. I t was undertaken w i t h the hope pf r e t a i n i n g most f e a t u r e s of " n a t u r a l " s i t u -a t i o n s , y e t a l l o w i n g more c o n t r o l over the f e e d i n g s i t u a t i o n and a more p o w e r f u l s t a t i s t i c a l a n a l y s i s . Four s m a l l rainbow t r o u t were p l a c e d i n t o each of four ponds ( F i g u r e 6) and t h e i r f o o d observed r e p e a t e d l y . To each pond was added substratum and organisms from the F i s h i n g Pond i n a p p r o x i m a t e l y the same d e n s i t y as p r e s e n t t h e r e . The same source of water s u p p l i e d the F i s h i n g Pond and the s m a l l ponds ( f l o w : 94 to 369 m l / s e c ) . 2 Some f l o a t i n g a l g a l mat (2600 cm ) c o n t a i n i n g p r e y organisms was c o l l e c t e d from the F i s h i n g Pond and p l a c e d i n t o the middle s e c t i o n of each s m a l l pond. The purpose of p a r t i t i o n -i n g the ponds i n t o s e c t i o n s was to f a c i l i t a t e f i s h c a p t u r e ; the passageways i n p a r t i t i o n s were c l o s e d o n l y w h i l e t r o u t were n e t t e d . The e n t i r e experiment was performed t w i c e : Table V I I FIGURE 6. I n s i d e dimensions (cm) of the ponds used i n the s m a l l pond exper iment . Each pond was p a r t i t i o n e d i n t o three s e c t i o n s w i t h passageways (pv) between s e c t i o n s . 31 o u t l i n e s t h e s l i g h t d i f f e r e n c e s between the two r e p l i c a t i o n s . A l t h o u g h f o u r ponds were s e t up b o t h months, o b s e r v a t i o n o f one pond was d i s c o n t i n u e d i n June b e c a u s e some t r o u t c o u l d n o t be c a p t u r e d a t t h e a p p r o p r i a t e t i m e s . A l l t r o u t had been h a t c h e d i n my l a b o r a t o r y and f e d c o m m e r c i a l , d r y f i s h f o o d u n t i l t h e y were u s e d i n t h e e x p e r i m e n t . Two groups o f f o u r t r o u t were u s e d f o r two p u r p o s e s : t o t e s t t h e s p e c i a l -i z a t i o n h y p o t h e s i s , and t o sample f o o d i n t h e ponds. The g r o u p u s e d t o t e s t t h e h y p o t h e s i s , " s a g e " t r o u t , were a l l o w e d t o r e m a i n i n the ponds between o b s e r v a t i o n s and were sampled r e p e a t e d l y . The g r o u p u s e d t o d e t e c t p o s s i b l e changes i n f o o d p r e s e n t , " n a i v e " t r o u t , were p l a c e d i n e a c h pond when-e v e r t h e sage t r o u t were sampled. E a c h n a i v e t r o u t was used once. I n each r e p l i c a t i o n , t h e sage and n a i v e t r o u t were n e t t e d f r o m the same h o l d i n g a q u a r i a . To p e r m i t i n d i v i d u a l r e c o g n i t i o n , sage t r o u t i n each pond were marked w i t h d i f f e r -e n t f i n c l i p s ( a n a l , a d i p o s e , v e n t r a l p o r t i o n o f c a u d a l , d o r s a l p o r t i o n o f c a u d a l , o r p o s t e r i o r p o r t i o n o f d o r s a l ) . The f i n c l i p s had no n o t i c e a b l e e f f e c t on swimming a b i l i t y o r s o c i a l s t a t u s . Two o f t h e f o u r ponds were sampled one day and t h e o t h e r two on t h e f o l l o w i n g day. C o n s e q u e n t l y , each group o f sage t r o u t was sampled no more f r e q u e n t l y t h a n e v e r y o t h e r day ( T a b l e V I I ) . D u r i n g s a m p l i n g , t h e sage t r o u t were removed w i t h a d i p n e t a t 1000 PST. T r o u t c a p t u r e r e q u i r e d l e s s t h a n 10 min p e r pond. The ponds were a l l o w e d to s e t t l e u n t i l 1100 when the n a i v e t r o u t were added and a l l o w e d t o f e e d 32 Table V I I . Comparison of June and August r e p l i c a t i o n s of the s m a l l pond experiment . REPLICATE June 2-26 A u g . 8 - S e p t . 3 S tock of Rainbow Trout Domestic (Trout Lodge S p r i n g s , I n c . , Tacoma, W ash . , USA) W i l d (Loon L a k e , B. C . 51 121 SE) CHARACTER-ISTICS OF TROUT Age (months) I n i t i a l l e n g t h (range i n mm) Average growth (mm) 12 63 - 78 not measured (about 10) 43 - 48 13.6 PROCEDURE Number of o b -s e r v a t i o n t imes 8 10 Number ponds a n a l y z e d 3 4 Number foods a n a l y z e d 8 5 Days food sampled 1, 3, 5, 7, 1, 3, 5, 7, 9, 11 , ( from s t a r t ) 9, 1 1 , 17, 24 13, 17, 19, 26 Days b e h a v i o r observed none 9, 11 , 13 33 f o r 2 h r . A f t e r t h e n a i v e f i s h were n e t t e d , the ponds were a g a i n a l l o w e d t o s e t t l e u n t i l t h e sage f i s h were r e t u r n e d a t 1400. The f o o d e a t e n by each sage and n a i v e t r o u t was sampled by stomach f l u s h i n g a f t e r a n e s t h e s i a . The a p p a r a t u s f o r stomach f l u s h i n g was a s i n g l e t u b e made o f a h y p o d e r m i c s y r i n g e and p o l y e t h y l e n e c a n n u l a . The c a n n u l a was i n t r o d u c e d i n t o the stomach and w a t e r i n j e c t e d w i t h t h e s y r i n g e . Y a t e r t o g e t h e r w i t h f o o d f l o w e d out a l o n g t h e c a n n u l a i n t o a c o l -l e c t i n g d i s h . The f o o d was c o u n t e d and p r e s e r v e d i n 10$ f o r m a l i n . The f o o d i n e a c h c a t e g o r y was combined by ponds and p e r i o d s o f 8 d a y s . The combined f o o d samples were d r i e d (16 h r and a t 50° C) and w e i g h e d ( t o 0.1 mg) i n o r d e r t o e s t i m a t e the a v e r a g e w e i g h t o f f o o d c a t e g o r i e s s e p a r a t e l y by t i m e p e r i o d and pond ( c a t e g o r i e s w i t h few i n d i v i d u a l ' s were combined f o r 2 or 4 p o n d s ) . The number d a t a were m u l t i p l i e d by the a p p r o p r i a t e w e i g h t e s t i m a t e t o o b t a i n d a t a u s e d i n a n a l y s e s o f v a r i a n c e . D u r i n g t h e A u g u s t r e p l i c a t i o n ^ ' I made some p r e l i m i n a r y o b s e r v a t i o n s on t h e f e e d i n g b e h a v i o u r o f sage t r o u t p r i o r t o s a m p l i n g t h e i r f o o d ( T a b l e V I I ) . The day b e f o r e s u c h o b s e r -v a t i o n , a t 1430 PST, t h e sage f i s h were removed f r o m t h e i r pond and h e l d i n t h e l a b o r a t o r y o v e r n i g h t w i t h o u t f o o d . They were r e t u r n e d t o t h e i r pond a t 0800 and o b s e r v e d b e f o r e r e m o v a l and stomach f l u s h i n g . I o b s e r v e d each i n d i v i d u a l i n a pond f o r f o u r 3-min p e r i o d s . 34 R e s u l t s of S m a l l Fond Experiment R e s u l t s of the s m a l l pond experiment are p r e s e n t e d i n T a b l e VHT and summarized i n Table IX. W i t h n a i v e t r o u t , the main e f f e c t of time was s m a l l . T h i s i n d i c a t e s t h a t the t o t a l weight of prey eaten d i d not change d u r i n g the course of the experiment , i m p l y i n g t h a t the same amount of food was always p r e s e n t . More i m p o r t a n t l y , the i n t e r a t i o n between k i n d of prey and time was s m a l l i n b o t h r e p l i c a t i o n s . T h i s i n d i c a t e s t h a t the r e l a t i v e abundance of d i f f e r e n t k i n d s of prey was c o n s t a n t . With sage t r o u t , the main e f f e c t of k i n d of p r e y was l a r g e i n boththe June and August r e p l i c a t i o n s ( T a b l e s V I I I and I X ) . T h i s i n d i c a t e s t h a t the t r o u t ate more of some k i n d s of prey than o t h e r s , which i s not v e r y s u r p r i s i n g . The i m p o r -t a n t f i n d i n g i s t h a t the i n t e r a c t i o n between i n d i v i d u a l t r o u t and k i n d of p r e y was l a r g e i n b o t h r e p l i c a t i o n s . T h i s means t h a t d i f f e r e n t i n d i v i d u a l s w i t h i n a pond s e l e c t e d d i f f e r e n t k i n d s of prey r e l a t i v e to other i n d i v i d u a l s . In other words, t h e r e was prey s p e c i a l i z a t i o n . To d e s c r i b e the development of prey s p e c i a l i z a t i o n , data were chosen f o r ponds where s p e c i a l i z a t i o n was the most and l e a s t obvious i n the f i r s t f o u r samples ( F i g u r e s 7 and 8). Not a l l food c a t e g o r i e s i n the f i g u r e s were used i n the a n a l y s e s . In b o t h a n a l y s e s , the ca tegory other was o m i t t e d ; i n the June r e p l i c a t e , few d i p t e r a pupae were ea ten , so t h i s c a t e g o r y was a l s o o m i t t e d . When t h e r e was a h i g h degree of s p e c i a l i z a t i o n , most i n d i v i d u a l s ate a c h a r a c t e r i s t i c a s s o r t -35 T a b l e V I I I . A n a l y s e s of v a r i a n c e of weights of prey eaten i n the s m a l l pond experiment . JUNE REPLICATION AUGUST REPLICATION Source of V a r i a t i o n df MEAN F P < df MEAN F P < SQUARE SQUARE Naive t r o u t Naive t r o u t K i n d of Prey (K) 7 34. 49 1 . 2 .310 4 22. 44 52. 9 .001 Pond (P) 2 56. 13 1 .9 .150 3 1 . 72 4. 1 .008 Time (T) 7 50. 60 1 . 7 .100 9 0. 41 1 . 0 .500 K x P -14 '25. 38 0 .9 .750 12 1 . 71 4. 0 .001 K x T 49 32. 74 1 . 1 .270 36 0. 41 1 . 0 .500 P x T 14 41 . 62 1 .4 .140 27 0. 49 1 . 2 .270 K x P x T 98 31 . 43 1 . 1 .300 108 0. 51 1 . 2 .086 Remainder 576 29. 11 600 0. 42 Sage t r o u t Sage t r o u t I n d i v i d u a l s (I) 3 4.21 0.4 1.0 3 1.15 1 .4 .250 K i n d of Prey (K) 7 25.26 2.4 .025 4 106.60 128.9 .001 Pond (P) 2 50.12 4 .8 .010 3 0 .77 0.9 . 500 Time (T) 7 18.98 1.8 .086 9 3.61 4 .4 .001 I x K 21 39.00 3 .7 .001 12 2.69 3.3 .001 I x P 6 24.55 2.3 .040 9 0.98 1 .2 .303 I x T 21 9.59 0.9 .750 27 0.66 0.8 .750 K x P 14 44.60 4.2 .001 12 5.31 6.4 .001 K x T 49 27.15 2.6 .001 36 1 .81 2.2 .001 P x T 14 8.25 0.8 .750 27 1.15 1 .4 .095 I x K x P 42 24.80 2.4 .001 36 1.18 1.4 .057 I x K x T 147 12.72 1.2 .090 108 1 .20 1.4 .008 I x P x T 42 9.41 0.9 1 .00 81 0.85 1 .0 .432 K x P x T 98 1 5.44 1.5 .008 108 1 .34 1.6 .001 I x K x P x T 294 10.51 324 0.83 (Remainder) 36 T a b l e IX. S t a t i s t i c a l l y s i g n i f i c a n t e f f e c t s i n the s m a l l pond experiment . The symbols are d e f i n e d i n Table V I I I . Naive Sage . M a i n e f f e c t s R e p l i c a t i o n I I n t e r a c t i o n None None K, P IK, I P , KP, KT, IKP, KPT Main e f f e c t s R e p l i c a t i o n -11^ Int e r a c t i o n K, P KP K, T IK, KP, K T , IKT, KPT FIGURE 7. Food eaten by i n d i v i d u a l s i n ponds where low or h i g h s p e c i a l i z a t i o n was apparent d u r i n g the f i r s t week (June r e p l i c a t i o n ) . PER CENT OF TOTAL FOOD COPEPODA CLADOCERA EPHEMEROPTERA L O D O N A T A LARVA CERATOPOGONIDAE L CHIRONOA/IDAE L DIPTERA PUPA INSECTA ADULT * GASTROPODA 5 OTHER n o c w O O o C O P E P O D A C L A D O C E R A EPHEMEROPTERA L O D O N A T A LARVA C E R A T O P O G O N I D A E L CHIRONOMIDAE L DIPTERA PUPA INSECTA ADULT GASTROPODA OTHER I'miiiillillmilAhlliliu \ -1 FIGURE 8. Food eaten by i n d i v i d u a l s i n ponds where low or high s p e c i a l i z a t i o n was apparent d u r i n g the f i r s t week (August r e p l i c a t i o n ) . PER CENT CF TOTAL FTEO 8 6 B 8 3 8 8 § P P P P P P P P P P P P P P P P P PLANKTON EftOERLPTEPA L CWRONCMIDAE LARVA OIPTCPA rLT-A INSECTA AOLF OTHER FLAWTCN EPHEkGCPTERA L MfiONCMlLAE: LARVA •IPTERA FLPA INEECTA AO-LT DTh€R PER CENT OF TOTAL FOOD S 8 8 6 1 S 8 S B B § P P P P P P P P P P S 8 8 S B S g 8 8 § P P P P P P P P P P ? s s s o z o o -o o > o z 00 39 ment of foods on each o b s e r v a t i o n and d i f f e r e n t i n d i v i d u a l s ate d i f f e r e n t k i n d s of p r e y . Yhen l e s s s p e c i a l i z a t i o n o c c u r r e d , there were fewer d i f f e r e n c e s among the i n d i v i d u a l s and l e s s c o n s i s t e n c y i n the type of food eaten by each i n d i -v i d u a l . As o u t l i n e d p r e v i o u s l y , I observed the b e h a v i o r of sage t r o u t i n two ponds d u r i n g the August r e p l i c a t i o n . The i n d i -v i d u a l s began f e e d i n g a few minutes a f t e r b e i n g r e t u r n e d to t h e i r pond. They moved f r e e l y between compartments, and f r e -q u e n t l y f o l l o w e d and seemed to seek out other i n d i v i d u a l s . The f r e q u e n c y of f e e d i n g b e h a v i o r decreased and t h a t of agon-i s t i c b e h a v i o r , as d e s c r i b e d by S t r i n g e r and Hoar (1955), i n c r e a s e d toward the end of an o b s e r v a t i o n s e s s i o n . A l t h o u g h c h a s i n g , n i p p i n g , and l a t e r a l d i s p l a y i n g were common, t h e r e was no apparent t e r r i t o r i a l i t y ( s i t e a t t a c h m e n t ) . No s u b m i s -s i v e d i s p l a y or c o l o r a t i o n was o b s e r v e d . S t r i k e s were the most conspicuous aspect of f e e d i n g b e h a v i o r . A s t r i k e c o n s i s t e d of an a c c e l e r a t e d swim i n a d i r e c t l i n e w i t h an o b j e c t , c u l m i n a t i n g w i t h i n g e s t i o n . In some s t r i k e s , i t was i m p o s s i b l e to r e c o g n i z e the k i n d of prey e a t e n ; o ther s t r i k e s were d i r e c t e d at n o n - f o o d o b j e c t s . From the middle of a compartment, t r o u t sometimes s t r u c k o b j e c t s at any other p o i n t w i t h i n the compartment. S t r i k e s were made when t r o u t had been s t a t i o n a r y f o r s e v e r a l minutes and when they had been swimming s l o w l y , presumably s e a r c h i n g . S t r i k e s were sometimes i n t e r s p e r s e d between bouts of a g o n i s t i c b e -h a v i o r . There was no s i n g l e , w e l l d e f i n e d s e a r c h i n g p a t t e r n . 40 I n d i v i d u a l s d i d not a l l s t r i k e w i t h the same f requency at o b j e c t s i n d i f f e r e n t s t r a t a of the ponds ( subst ra tum, s u r f a c e , water column, and w a l l ; Q^ 2 = 74 .2 , 21 d f , p < 0 .001) . How-ever , a l l i n d i v i d u a l s made at l e a s t one s t r i k e i n a l l s t r a t a . My o b s e r v a t i o n s were not s u f f i c i e n t l y e x t e n s i v e to d e t e c t more s u b t l e d i f f e r e n c e s i n s e a r c h i n g b e h a v i o r . 3, 41 DISCUSSION The k i n d s of prey eaten by i n d i v i d u a l s captured from a t r o u t p o p u l a t i o n were seldom d i s t r i b u t e d a t random among them. As o u t l i n e d i n the i n t r o d u c t i o n , such food h e t e r o g e n e i t y has been observed i n s e v e r a l p r e d a t o r s . By i t s e l f , h e t e r o g e n e i t y does not n e c e s s a r i l y mean t h a t s p e c i a l i z a t i o n has o c c u r r e d . H e t e r o g e n e i t y may occur even though i n d i v i d u a l s do not eat c h a r a c t e r i s t i c assortments of f o o d on d i f f e r e n t d a y s . For i n s t a n c e , food h e t e r o g e n e i t y might have r e s u l t e d because prey d i s t r i b u t i o n s were contagious i n space or t i m e ; i t c o u l d a l s o have r e s u l t e d from r a p i d l e a r n i n g l i k e t h a t observed i n crows ( C r o z e , 1970). However, i n d i v i d u a l t r o u t d i d eat c h a r a c t e r i s t i c k i n d s of p r e y on d i f f e r e n t days . T h i s seemed to be t r u e of a l l t h r e e t r o u t s p e c i e s i n M a r s h a l l Creek and of rainbow t r o u t i n the F i s h i n g Pond. S p e c i a l i z a t i o n was observed i n both a domestic and a w i l d s t r a i n of rainbow t r o u t i n the s m a l l pond experiment . These f i n d i n g s suggest that there were some m o r p h o l o g i c a l or l a s t i n g b e h a v i o r a l d i f f e r e n c e s p r o d u c i n g not o n l y f o o d h e t e r o g e n e i t y but a l s o food s p e c i a l i z a t i o n . Thus the t r o u t p o p u l a t i o n s c o n s i s t e d of i n d i v i d u a l s each p r e y i n g on o n l y p a r t of the e n t i r e spectrum of p r e y types consumed by a l l t r o u t i n the p o p u l a t i o n . T h i s g e n e r a l i z a t i o n was t r u e on any day and f o r p e r i o d s of many days as w e l l . Prey s p e c i a l i z a t i o n p r o b a b l y occurs i n most s p e c i e s of polyphagous f i s h i n n o r t h temperate areas and, q u i t e 42 p o s s i b l y , i n many polyphagous p r e d a t o r s other than f i s h . Both the prey c l a s s i f i c a t i o n systems and the s i m i l a r i t y measures were a r b i t r a r y . A b e t t e r system of prey c l a s s i f i -c a t i o n would have been t h a t used by t r o u t themselves—because s p l i t t i n g c a t e g o r i e s t r o u t lump would produce low food s i m -i l a r i t y measures as would lumping c a t e g o r i e s t r o u t s p l i t . (The prey taxonomy used by the t r o u t might be determined ex-p e r i m e n t a l l y or w i t h stomach content data independent of t h a t used i n h y p o t h e s i s t e s t i n g , ) . Use of d i f f e r e n t food c a t e g o r i e s would have produced d i f f e r e n t c o r r e l a t i o n c o e f f i c i e n t s between p a i r s of food samples . L i k e w i s e , use of a d i f f e r e n t s i m i l a r -i t y measure would have ranked p a i r s of f o o d samples d i f f e r -e n t l y . However, both the food c a t e g o r i e s and the s i m i l a r i t y measure were used i n a r e l a t i v e and not an a b s o l u t e manner, as w i t h i n s and betweens were compared. C o n s e q u e n t l y , a d i f f e r e n t food c l a s s i f i c a t i o n or s i m i l a r i t y measure would presumably show food s p e c i a l i z a t i o n , a l t h o u g h perhaps not w i t h the same s t a t i s t i c a l e f f i c i e n c y . As d e s c r i b e d p r e v i o u s l y , there i s some evidence of prey s p e c i a l i z a t i o n among t i t s and salamanders ( T i n b e r g e n , 1960; N e i s h , MS f 1970) . F o r both p r e d a t o r s , data i s p r e s e n t e d o n l y f o r i n d i v i d u a l s which had unusual f e e d i n g b e h a v i o r ; c o n s e -q u e n t l y , s p e c i a l i z a t i o n may not be t y p i c a l of these p r e d a t o r s . Food s p e c i a l i z a t i o n has been observed among i n d i v i d u a l animals o f f e r e d excess food i n the l a b o r a t o r y . Brown (1969) found t h a t pigeons ate d i f f e r e n t k i n d s of f o o d i n p r o p o r t i o n s c h a r a c t e r i s t i c f o r an i n d i v i d u a l . I have observed the same i n 43 t r o u t . By t h e m s e l v e s , these f i n d i n g s do not i m p l y t h a t food s p e c i a l i z a t i o n n e c e s s a r i l y occurs i n f i e l d s i t u a t i o n s , as most components of p r e y l o c a t i o n and c a p t u r e . b e h a v i o r were e l i m i n a t e d . A d i f f e r e n c e between food s e l e c t i o n i n the l a b -o r a t o r y and f i e l d i s l i k e the d i f f e r e n c e between food s e l e c -t i o n by weal thy men i n r e s t a u r a n t s and by men, w i t h o u t accoutrements , i n w i l d e r n e s s . Food d i s t r i b u t i o n s of the t r o u t captured i n the stream were examined to determine whether t r o u t w i t h p o s i t i v e or n e g a t i v e s p e c i a l i z a t i o n measures had eaten an unusual a s s o r t -ment of f o o d s . W i t h some minor d i f f e r e n c e s , food s p e c t r a of such t r o u t were s i m i l a r to each other and to the spectrum f o r i n d i v i d u a l s not r e c a p t u r e d . Trout w i t h h i g h measures had eaten more of the prey types p r o b a b l y o b t a i n e d through f o r a g -i n g , whereas those w i t h low measures had eaten more of the prey types which were p r o b a b l y p r e s e n t i n an area f o r o n l y a s h o r t t i m e . There was no evidence t h a t some i n d i v i d u a l s s p e c i a l i z e d and others d i d n o t . I n s t e a d , a l l i n d i v i d u a l s seemed to s p e c i a l i z e some of the t i m e . These f i n d i n g s are c o n s i s t e n t w i t h d e s c r i p t i o n s of t r o u t as o p p o r t u n i s t i c p r e d a t o r s . Many s t u d i e s of food eaten by p o p u l a t i o n s of t r o u t at d i f f e r e n t t imes or d i f f e r e n t areas show great f l e x -i b i l i t y i n k i n d of prey eaten ( L a r k i n , 1956). In the c r e e k , the degree of s p e c i a l i z a t i o n was g r e a t e s t when i n d i v i d u a l s were r e c a p t u r e d w i t h i n 20 d a y s , and none was e v i d e n t between 30 and 50 d a y s . At s t i l l l o n g e r i n t e r -v a l s (60-250 d a y s ) , however, the data suggested t h a t t h e r e 44 was s p e c i a l i z a t i o n . Thus , some s p e c i a l i z a t i o n may p e r s i s t f o r h a l f a year or more. Such l e n g t h y s p e c i a l i z a t i o n was p o s s i b l e i n M a r s h a l l Creek because the prey p o p u l a t i o n s seemed s t a b l e i n comparison w i t h some t r o u t h a b i t a t s . No c h a r a c t e r i s t i c s of i n d i v i d u a l t r o u t were found which were s t r o n g l y c o r r e l a t e d w i t h the tendency to s p e c i a l i z e . There were s l i g h t , p o s i t i v e c o r r e l a t i o n s between food s i m i l a r -i t y measures and both weight and number of k i n d s of food e a t e n . Even i f the c o r r e l a t i o n were s t r o n g e r , I would not suggest t h a t e i t h e r was c a u s a l w i t h o u t i n f o r m a t i o n about the e f f e c t of sample s i z e (number of prey i n a stomach) on the v a l u e s o f s i m i l a r i t y measures o b t a i n e d . The l a r g e s t c o r r e l -a t i o n s were p o s i t i v e ones between growth and number of k i n d s of prey ea ten . They were somewhat l a r g e r c o e f f i c i e n t s than those between growth and t o t a l weight of f o o d . However, i n a c c u r a c i e s i n the l e n g t h measurements prevented good e s t i -mates of growth, some of which were n e g a t i v e . There was no evidence t h a t f o o d of i n d i v i d u a l s captured and r e c a p t u r e d i n the same area was more s i m i l a r than food of those c a p t u r e d and r e c a p t u r e d i n d i f f e r e n t a r e a s . T h i s i m p l i e s e i t h e r t h a t the s u b s e c t i o n s of stream were homogeneous i n r e l a t i v e abundance of p o t e n t i a l food or t h a t the f e e d i n g b e h a v i o r of the t r o u t was more important i n d e t e r m i n i n g food eaten than d i f f e r e n c e s among s u b s e c t i o n s . Between S e c t i o n 1 and the other s e c t i o n s , there were c o n s i d e r a b l e d i f f e r e n c e s i n p h y s i c a l f e a t u r e s and i n food a c t u a l l y eaten by t r o u t . T h i s suggests t h a t some b e h a v i o r a l c o n s i s t e n c y of i n d i v i d u a l 45 t r o u t enabled them to eat s i m i l a r f o o d i n d i f f e r e n t s u b s e c t i o n s of s tream. S e v e r a l o b s e r v a t i o n s suggested t h a t t r o u t f r e q u e n t l y l e f t s tream s e c t i o n s , p a r t l y i n response to the c o l l e c t i n g methods. Most i n d i v i d u a l s were captured o n l y once ; t r o u t d e n s i t y decreased w i t h i n a l l s e c t i o n s ; and a n g l e r s captured some t r o u t o u t s i d e the s tudy a r e a . In a r e l a t i v e l y u n d i s t u r b e d stream, J e n k i n s (1969) observed that 20-30% of the i n d i v i d u a l t r o u t i n an area were t r a n s i e n t . In a d d i t i o n to n a t u r a l movements, e l e c t r o f i s h i n g p r o b a b l y induced many i n d i v i d u a l s to l e a v e the study area -. In the l a b o r a t o r y , most t r o u t l e a r n e d to a v o i d an area where they r e c e i v e d an e l e c t r i c shock i n 3 t r i a l s ( J . M. B l a c k b u r n , p e r s o n a l communicat ion) . In t h e s m a l l pond experiment , the b e h a v i o r a l mechanism which seemed most l i k e l y to have produced the f o o d s p e c i a l i -z a t i o n was d i f f e r e n t i a l response to v i s u a l s t i m u l i . However, the h y p o t h e s i s t h a t t h i s mechanism i s an adequate e x p l a n a t i o n was not t e s t e d . There was no evidence t h a t i n d i v i d u a l s remained i n d i f f e r e n t compartments or r e g i o n s of a compart -ment. A g o n i s t i c s o c i a l b e h a v i o r had no apparent i n f l u e n c e on the amount of prey eaten , p r o b a b l y because food was abundant and d i s p e r s e d . Magnuson (1962) found t h a t a g o n i s t i c b e h a v i o r i n medaka had no i n f l u e n c e on amount eaten i n s i m i l a r s i t u a t i o n s . T h e i r s o c i a l b e h a v i o r suggested t h a t i n d i v i d u a l s c o u l d l e a r n about p r e y from each o t h e r ; such l e a r n i n g o c c u r r e d i n great t i t s ( K r e b s , MacRoberts , and C u l l e n , i n p r e s s ) . There were no marked d i f f e r e n c e s among the i n d i v i d u a l s 46 i n s e a r c h i n g t e c h n i q u e . Y e a r l i n g rainbow t r o u t c o l l e c t e d from a lake adopted a s t a n d a r d s e a r c h i n g p a t t e r n when f e d b e n t h i c p r e y i n l a r g e a q u a r i a (Ware, MS 1971). The t r o u t would a t t a c k prey w h i l e swimming s l o w l y 10 to 15 cm above the substratum w i t h t h e i r heads i n c l i n e d downward at an angle of about 1 5 ° . T h i s c h a r a c t e r i s t i c s e a r c h i n g p a t t e r n was not observed i n the t r o u t of the s m a l l pond experiment which had not eaten l i v e p r e y u n t i l the experiment . There were d i f f e r e n c e s i n the f r e q u e n c y w i t h which d i f f e r e n t i n d i -v i d u a l s a t t a c k e d o b j e c t s i n d i f f e r e n t s t r a t a of the ponds. T h i s c o u l d have r e f l e c t e d d i f f e r e n c e s i n c o n d i t i o n i n g to s t i m u l i a s s o c i a t e d w i t h d i f f e r e n t types of p r e y . Whatever produced prey s p e c i a l i z a t i o n i n the s m a l l ponds d i d not n e c e s s a r i l y produce i t under o ther c o n d i t i o n s . R e l a -t i v e to the s i z e and d e n s i t y of t r o u t , the dimensions of the ponds may not have been r e a l i s t i c . Moreover , the prey from the F i s h i n g Pond had been exposed to p r e d a t i o n by t r o u t much l a r g e r than those i n the s m a l l ponds. F o r t h i s r e a s o n , the prey d e n s i t i e s , prey q u a l i t y , or b o t h , may not have been at e q u i l i b r i u m i n the new p r e d a t i o n system. More e x t e n s i v e o b s e r v a t i o n of f e e d i n g by t r o u t i n the s m a l l ponds would p r o b a b l y have r e v e a l e d s e v e r a l other b e h a v i o r a l d i f f e r e n c e s c o n t r i b u t i n g to d i f f e r e n c e s i n prey ea ten . S i n c e t r o u t i n the s m a l l ponds had e x p e r i e n c e d l i v e prey f o r o n l y a few weeks, they may not have developed i n d i v i d u a l d i f f e r e n c e s of the same k i n d as t r o u t i n the stream and pond. I t seems u n l i k e l y t h a t a l l i n d i v i d u a l d i f f e r e n c e s i n ;.. 47 food eaten by t r o u t , i n f i e l d s i t u a t i o n s , r e s u l t from the same mechanism. Some k i n d s of p r e y eaten d i f f e r c o n s i d e r a b l y i n t h e i r s p a t i a l and temporal d i s t r i b u t i o n , t h e i r ease of c a p t u r e , and t h e i r appearance . C o n s e q u e n t l y , not a l l k i n d s can be c a p t u r e d at the same p l a c e and time by t r o u t w i t h the same s e a r c h i n g and c a p t u r i n g t e c h n i q u e , c o n d i t i o n e d to a l i m i t e d se t of food s t i m u l i . Thus , t h e r e are many s o r t s of i n d i v i d u a l and envi ronmenta l d i f f e r e n c e which would cause d i f f e r e n c e s i n the k i n d of prey ea ten . T h i s s tudy d i d not attempt to determine, e x p e r i m e n t a l l y , any consequences of s p e c i a l i z a t i o n to e i t h e r the p r e d a t o r or the p r e y . Some p o s s i b l e consequences f o r prey p o p u l a t i o n s have been e x p l o r e d by Murdoch (1969) and Reed (MS 1971). Presumably , s p e c i a l i z a t i o n i s i n some way a d a p t i v e , or i t would not o c c u r . In t h i s s t u d y , the o n l y i n f o r m a t i o n about p o s s i b l e consequences of s p e c i a l i z a t i o n to the t r o u t them-s e l v e s were c o r r e l a t i o n s . 48 BIBLIOGRAPHY A l a b a s t e r , J . S . , and ¥ . G. H a r t l e y . 1962. The e f f i c i e n c y of a d i r e c t c u r r e n t e l e c t r i c f i s h i n g method i n t r o u t s treams. J . Anim. E c o l . 31: 385-388. A l l e n , K. R. 1941. S t u d i e s on the b i o l o g y of the e a r l y s tages of salmon (Salmo s a l a r ) . J . Anim. E c o l . 10: 47-76. B e l l , G. R. 1964. A guide to the p r o p e r t i e s , c h a r a c t e r i s t i c s , and uses of some g e n e r a l a n a e s t h e t i c s f o r f i s h . B u l l . F i s h . Res . Bd . Can. 148, 4p. Brown, R. G. B. 1969. Seed s e l e c t i o n by p i g e o n s . Behaviour 34: 115-131. C r o z e , H . 1970. S e a r c h i n g image i n c a r r i o n crows. Z . T i e r -p s y c h o l . , supplement 5, 86 p. E l s o n , P. F . 1950. U s e f u l n e s s of e l e c t r o f i s h i n g methods. Can. F i s h C u l t . 9: 3-12. H a r r i s , M. P. 1965. The food of some Larus g u l l s . I b i s 107: 43-53. H a s k e l l , D. C . , and R. G. Z i l l i o x . 1940. F u r t h e r developments of the e l e c t r i c a l method of c o l l e c t i n g f i s h . T r a n s . Am. F i s h . Soc . 70: 404-409. I v l e v , V . S. 1961. E x p e r i m e n t a l ecology of the f e e d i n g of f i s h e s . Y a l e U n i v e r s i t y P r e s s , New Haven. p . 66-72. J e n k i n s , T . M . , J r . 1969. S o c i a l s t r u c t u r e , p o s i t i o n c h o i c e and m i c r o d i s t r i b u t i o n of two t r o u t s p e c i e s (Salmo t r u t t a and Salmo g a i r d n e r i ) r e s i d e n t i n mountain streams. Anim. Behav. Monogr. 2: 56-123. K r e b s , J . R . , M. H . MacRoberts , and J . M. C u l l e n . i n p r e s s . F l o c k i n g and f e e d i n g i n the Great T i t (Parus m a j o r ) ; an e x p e r i m e n t a l s t u d y . L a r k i n , P. A . 1956. I n t e r s p e c i f i c c o m p e t i t i o n and p o p u l a t i o n c o n t r o l i n f r e s h w a t e r f i s h . J . F i s h . Res . Bd . Can. 13: 327-342. L e w o n t i n , R. C , and J . F e l s e n s t e i n . 1 965. The r o b u s t n e s s of homogeneity t e s t s i n 2 x n t a b l e s . B i o m e t r i c s 21: 19-33. 49 Magnuson, J . J . 1962. An a n a l y s i s of a g g r e s s i v e b e h a v i o r , growth, and c o m p e t i t i o n f o r food and space i n medaka ( O r y z i a s l a t i p e s ( P i s c e s , C y p r i n o d o n t i d a e ) ) . Can. J . Z o o l . 40: 313-363. Murdoch, ¥ . ¥ . 1969. S w i t c h i n g i n g e n e r a l p r e d a t o r s : e x p e r -iments on p r e d a t o r s p e c i f i c i t y and s t a b i l i t y of prey p o p -u l a t i o n s . E c o l . Monogr. 39: 335-354. N e i s h , I . C. 1970. A comparat ive a n a l y s i s of the f e e d i n g behaviour of two salamander p o p u l a t i o n s i n M a r i o n L a k e , B. C. P h . D . T h e s i s , Department of Z o o l o g y , U n i v e r s i t y of B r i t i s h C o l u m b i a , 108 p. P a r k e r , R. R . , and P. A. L a r k i n . 1959. A concept of growth i n f i s h e s . J . F i s h . Res . B d . Can. 16: 721-745. Reed, R. C. 1971. An e x p e r i m e n t a l s tudy of p r e y s e l e c t i o n and r e g u l a t o r y c a p a c i t y of b l u e g i l l s u n f i s h (Lepomis . m a c r o c h i r u s ) . M. A . T h e s i s , Department of B i o l o g y , U n i v e r s i t y of C a l i f o r n i a , Santa B a r b a r a , 106 p. Seaburg , K. G. 1957. A stomach sampler f o r l i v e f i s h . P r o g v e . F i s h C u l t . 19: 137-139. S t e e l , R. G. D . , and J . H . T o r r i e . 1960. P r i n c i p l e s and procedures of s t a t i s t i c ^ w i t h s p e c i a l r e f e r e n c e to the b i o l o g i c a l s c i e n c e s . M c G r a w - H i l l , New Y o r k , p . 183-193. S t r i n g e r , G. E . , and ¥ . S. Hoar . 1955. A g g r e s s i v e b e h a v i o r of u n d e r y e a r l i n g Kamloops t r o u t . Can. J . Z o o l . 33: 148-160. T i n b e r g e n , L . 1960. The n a t u r a l c o n t r o l of i n s e c t s i n pinewoods. I . F a c t o r s i n f l u e n c i n g the i n t e n s i t y of p r e d a t i o n by s o n g b i r d s . A r c h s . n e e r l . Z o o l . 13: 265-343. Y a r e , D. M. 1971. The p r e d a t o r y b e h a v i o u r of rainbow t r o u t (Salmo g a i r d n e r i ) . P h . D . T h e s i s , Department of Z o o l o g y , U n i v e r s i t y of B r i t i s h Columbia 158 p . Y i n d e l l , J . T . , and D. 0. N o r r i s . 1969. G a s t r i c d i g e s t i o n and e v a c u a t i o n i n rainbow t r o u t . P r o g v e . F i s h C u l t . 31: 20-26. 50 APPENDIX Length d i s t r i b u t i o n (n = 406) of a l l t r o u t s p e c i e s i n M a r s h a l l C r e e k . The data i n c l u d e l e n g t h s of a l l f i s h whether c a p t u r e d or r e c a p t u r e d . 51 50 4 0 3 •A > O u a) 3 0 . . § 2 0 Pi 10 5 1 i i PI PS R5 ii 150 200 250 Fori'. Length (mm) 3 0 0 350 D i s t r i b u t i o n of s p e c i a l i z a t i o n measures (n = 248) f o r a l l t h r e e t r o u t s p e c i e s i n M a r s h a l l Creek. The maximim time i n t e r v a l between capture and r e c a p t u r e was 250 days . Number of Individuals i-1 o ro o OJ o o i o i N J tn (0 o H -Ol H I-1-N rt H * o 3 £ CD Ul C M N + o + NJ + + + o to FIGURE 3. Seasonal d i s t r i b u t i o n of s p e c i a l i z a t i o n measures f o r a l l three t r o u t s p e c i e s i n M a r s h a l l Creek . The maximum time i n t e r v a l between capture and r e c a p t u r e was 250 days . Specialization Measure (ZW - 23) > ro < o ro • ri tu ro J> ro o r-h "9 ro a cr 01 • ft ro o CJ •a rf s c 0) n ro a. H * SI 3 & D > •tt> rr n ro • SJ ro ON 0 01 V rt 3 C 01 n •< ro a ro U) I CJ o I to I H O o + r-> o + ro + u + • t • ( • • •»• • • • • • »• • • • • • • • » » » • • • • • • • • • • a* • • • • • • a • ££ 54 FEEDING HISTORY, PARENTAL STOCK, AND FOOD SELECTION IN RAINBOY TROUT ABSTRACT Feeding h i s t o r y and p a r e n t a l stock were manipulated to determine whether they could i n f l u e n c e food s e l e c t i o n i n young t r o u t , Salmo g a i r d n e r i Richardson. A f t e r 9 t r a i n i n g meals of one food, t r o u t s e l e c t e d that food, the f a m i l i a r one, when given a choice between i t and a novel food. (Most choice s i t u a t i o n s used h i g h and equal d e n s i t i e s of unconcealed foods w i t h i n a small area). S e l e c t i o n of the f a m i l i a r food occurred with s e v e r a l kinds of n o n - l i v i n g food. Trout t r a i n e d on l i v e prey, however, d i d not always s e l e c t the f a m i l i a r one when both prey were a l i v e , although they d i d when both prey were dead. Some c h a r a c t e r i s t i c s of the t r a i n i n g e f f e c t were i n v e s t -i g a t e d . As they became s a t i a t e d , t r o u t consumed r e l a t i v e l y more of the novel food. Duration of food d e p r i v a t i o n before a choice t e s t d i d not change the degree of s e l e c t i o n f o r the f a m i l i a r food. In a d d i t i o n to e a t i n g more of the f a m i l i a r food, t r o u t s t r u c k but r e j e c t e d r e l a t i v e l y more of the novel food. I n d i v i d u a l t r o u t t r a i n e d on two foods ate them i n pro p o r t i o n s which were c h a r a c t e r i s t i c f o r an i n d i v i d u a l . A f t e r they had learned to s e l e c t one food, t r o u t were given f u r t h e r t r a i n i n g on one of the f o l l o w i n g : the f a m i l i a r food, a novel food, or both. F u r t h e r t r a i n i n g on the f a m i l i a r food d i d not change the p r o p o r t i o n s e l e c t e d . Trout t r a i n e d 55 on one food f o r 12 meals and then on a second f o o d f o r 12 meals s e l e c t e d the second food when g i v e n a c h o i c e . When the i n i t i a l t r a i n i n g was f o l l o w e d by cont inuous f e e d i n g of b o t h f a m i l i a r and n o v e l f o o d , t r o u t c o n t i n u e d to s e l e c t the f a m i l i a r f o o d f o r 14 to 23 meals . A l l r e s u l t s suggested t h a t e f f e c t s of such f e e d i n g h i s t o r y would not g r e a t l y i n f l u e n c e food s e l e c t i o n i n n a t u r a l s i t u a t i o n s . Progeny of d i f f e r e n t p a r e n t a l s tocks were t e s t e d to determine whether p a r e n t a l food can i n f l u e n c e food s e l e c t e d by o f f s p r i n g . Eggs from t r o u t which ate d i f f e r e n t k i n d s of f o o d were h a t c h e d i n the l a b o r a t o r y . F o r t h e i r f i r s t meal , t r o u t were g i v e n c h o i c e s of the k i n d s of 'food eaten by the p a r e n t a l s t o c k s . In three main exper iments , the young t r o u t d i d not s e l e c t the type of f o o d commonly eaten by t h e i r p a r e n t s . 56 INTRODUCTION The aim of t h i s r e s e a r c h was to f i n d out whether d i f f e r -ences i n f e e d i n g h i s t o r y or p a r e n t a l s t o c k c o u l d produce d i f f e r e n c e s i n food chosen by i n d i v i d u a l t r o u t . I s t u d i e d t h i s problem i n t r o u t because I had observed h e t e r o g e n e i t y i n the food of a d u l t s c o l l e c t e d from a r i v e r , a s tream, and a pond. My experiments were des igned to show not why i n d i v -i d u a l d i f f e r e n c e s e x i s t i n n a t u r a l s i t u a t i o n s , but what can produce s i m i l a r d i f f e r e n c e s under c o n t r o l l e d c o n d i t i o n s . The two k i n d s of i n f o r m a t i o n may b e — b u t are not n e c e s s a r i l y — t h e same. Yhen g i v e n a c h o i c e between a f a m i l i a r and a n o v e l f o o d , many animals s e l e c t (eat i n g r e a t e r p r o p o r t i o n ) the type of food they have eaten p r e v i o u s l y . I w i l l use the term t r a i n i n g  b i a s to d e s c r i b e such s e l e c t i o n . T a b l e I l i s t s some animals which developed t r a i n i n g b i a s e s and o u t l i n e s the nature of the experiments used to s tudy them. Both v e r t e b r a t e s and i n v e r t -ebrates d e v e l o p t r a i n i n g b i a s e s f o r c e r t a i n f o o d s . The t h i r d column of Table I i n d i c a t e s whether an animal developed b i a s e s f o r a l l of the t r a i n i n g foods used by an exper imenter . There are c o n f l i c t i n g r e p o r t s about t r a i n i n g e f f e c t s i n mammals. Kuo (1967) c l a i m s to have produced b i a s e s i n cats and dogs but was unable to p u b l i s h the r e s u l t s . Bronson (1966) t r a i n e d r a t s from about 16 to 48 days a f t e r b i r t h , f i n d i n g no s e l e c t i o n of the f a m i l i a r f o o d . The t r a i n i n g b i a s e s among the animals l i s t e d i n Table I TABLE I . Comparison of experiments on t r a i n i n g b i a s i n d i f f e r e n t a n i m a l s . The words " y e s " and " n o " answer q u e s t i o n s i n d i c a t e d . P lus or minus i n d i c a t e whether any e x p e r i -ment d i d or d i d not use the m a t e r i a l and procedure i n d i c a t e d . A n i m a l ( s ) Reference B i a s e s p r o - D i d a l l a n i - Nature of the duced w i t h mals r e c e i v e a l l foods? food b e f o r e t r a i n i n g ? e x p e r i m e n t a l foods Second t r a i n i n g f o o d ( s ) a f t e r development of b i a s f o r one food s e d e n -t a r y a c t i v e . f a m i l i a r food n o v e l food f a m i l i a r & n o v e l food S t a r f i s h Marine s n a i l s L e p i d o p t e r a l a r v a e Landenberger , Tes 1968 Murdoch, 1969 No T i b o r , Hanson, No and D e t h i e r , 1969 Tes Yes No + + + + + + + Carp Salmon T r o u t Salamander I v l e v , 1955 ^ Yes L e B r a s s e u r , 1969 No Present s tudy Yes Henderson, MS 1970 Yes Yes Yes No No + + + ? + + + + + + Snapping t u r t l e Red-eared t u r t l e C h i c k e n Wood p i g e o n G u l l s Burghardt and Yes Hess , 1966 B u r g h a r d t , 1967 Yes Mahmoud and Yes Lavenda, 1969 Hess , 1962 Yes C a p r e t t a , 1969 Yes M a t h i a s s o n , 1967 No R a b i n o w i t c h , Yes 1968 No No No No No Yes No + + + + + + + + + 58 seem s i m i l a r i n t h a t a l l animals were t r a i n e d on m a i n l y one k i n d of f o o d f o r a known p e r i o d of t i m e , then g i v e n a s i m u l -taneous c h o i c e of f a m i l i a r and other f o o d s . In a l l c h o i c e t e s t s , the foods were present i n h i g h d e n s i t y w i t h i n a r e -s t r i c t e d area to e q u a l i z e p r o b a b i l i t i e s of c o n t a c t i n g each k i n d of f o o d . However, the s p e c i e s s t u d i e d are q u i t e d i v e r s e , and the d e t a i l s of the t e s t s i t u a t i o n s and c r i t e r i a f o r s e l -e c t i o n were a l l d i f f e r e n t . Moreover , d i f f e r e n t r e s e a r c h e r s i n t e n d e d to use the i n f o r m a t i o n f o r d i f f e r e n t purposes . Thus i t i s q u i t e p o s s i b l e t h a t t r a i n i n g b i a s e s are not the same i n a l l these animals and s i t u a t i o n s . F o r example, some workers argue t h a t a k i n d of i m p r i n t -i n g may occur f o r the f i r s t food e x p e r i e n c e d by a p r e c o c i a l animal (Hess , 1962; Burghardt and Hess , 1966). A n o n - f o o d s t i m u l u s to which d u c k l i n g s were i m p r i n t e d would e l i c i t f e e d i n g b e h a v i o r (Hoffman, S t r a t t o n , and Newby, 1969). Other workers argue t h a t s e l e c t i o n of the f i r s t k i n d of food eaten a f t e r h a t c h i n g p r o b a b l y r e s u l t s from a b e h a v i o r a l mechanism d i f f e r e n t from i m p r i n t i n g ( C a p r e t t a , 1969; Mahmoud and Lavenda , 1969). I t i s p o s s i b l e t h a t food i m p r i n t i n g i s a s p e c i a l k i n d of t r a i n i n g b i a s and t h a t there are other s p e c i a l k i n d s as w e l l . In at l e a s t one s p e c i e s , p a r e n t a l s tock can i n f l u e n c e f o o d s e l e c t i o n . Groups of young g a r t e r snakes , hatched i n the l a b o r a t o r y , s e l e c t e d d i f f e r e n t t e s t foods ( D i x , 1968; B u r g h a r d t , 1970). The parents of these snakes had been c o l l e c t e d from d i f f e r e n t geographic areas where they ate 59 d i f f e r e n t p r o p o r t i o n s of prey s p e c i e s . The young snakes s e l e c t e d s p e c i e s of prey commonly eaten by t h e i r p a r e n t s . M a t e r n a l d i e t d u r i n g the g e s t a t i o n p e r i o d had no apparent e f f e c t on food s e l e c t i o n (Burghardt , 1971). T a b l e I i n d i c a t e s the nature of the experiments used to s tudy e f f e c t s of f e e d i n g h i s t o r y i n t r o u t . Experiments to e s t a b l i s h t h a t t r o u t , l i k e o ther a n i m a l s , d e v e l o p t r a i n i n g b i a s e s were f o l l o w e d by experiments on f e e d i n g by t r o u t w i t h a t r a i n i n g b i a s . Other experiments were d e s i g n e d to show some e f f e c t s of f u r t h e r t r a i n i n g a f t e r one t r a i n i n g b i a s had been d e v e l o p e d . A l l experiments on the e f f e c t of p a r e n t -a l s t o c k were d e s i g n e d to determine whether d i f f e r e n c e s i n p a r e n t a l f e e d i n g have any i n f l u e n c e on f o o d s e l e c t i o n by progeny. 60 MATERIALS AND METHODS The e x p e r i m e n t a l animals Both domestic and w i l d s t r a i n s of rainbow t r o u t were used i n exper iments . Young of the w i l d s t r a i n s were hatched i n the l a b o r a t o r y , m a i n l y from eggs of a d u l t t r o u t n a t i v e to Loon Lake , B r i t i s h Columbia (51 121 S E ) . The domestic s t o c k was a l s o hatched i n the l a b o r a t o r y from eggs of f i s h c u l t u r e d under h a t c h e r y c o n d i t i o n s (Trout Lodge S p r i n g s , I n c . , Tacoma, ¥ a s h . USA) . The domestic s t o c k had been c u l t u r e d f o r at l e a s t 4 to 6 g e n e r a t i o n s , and each parent had been chosen from an i n i t i a l number of about 100 f r y . Y i t h i n exper iments , the t r o u t were n e a r l y the same s i z e and age when t r a i n e d and t e s t e d . A f t e r h a t c h i n g , t r o u t were h e l d w i t h o u t food u n t i l most of them began swimming i n the water column (about 30 d a y s ) . At t h i s t i m e , t h e i r f o r k l e n g t h ranged from 24 to 29 mm and, a f t e r 75 days w i t h f o o d , from 35 to 50 mm. F i s h were drawn f o r t r a i n i n g and t e s t i n g at random, but those w i t h p h y s i c a l d e f e c t s were r e j e c t e d . I n d i v i d u a l s which d i d not feed were not r e p l a c e d ; data f o r such f i s h were a n a l y z e d as m i s s i n g o b s e r v a t i o n s . L a b o r a t o r y c o n d i t i o n s My l a b o r a t o r y was l o c a t e d at the F r a s e r V a l l e y Trout H a t c h e r y , A b b o t s f o r d , B. C. Y a t e r was s u p p l i e d to i t from a s e t t l i n g pond f e d by s p r i n g s . Temperature and oxygen c o n c e n t r a t i o n w i t h i n h o l d i n g f a c i l i t i e s were c o n t r o l l e d by 61 r a t e of f low through those f a c i l i t i e s , so they f l u c t u a t e d w i t h c o n d i t i o n s i n the s e t t l i n g pond. Flow r a t e s to h o l d i n g a q u a r i a (25 by 50 by 25 cm) were set to a minimum of 3 m l / s e c , which p r o v i d e d water replacement i n 15 min to 3 h r . The ra te was a d j u s t e d f o r the number and s i z e of f i s h or eggs. The water temperature w i t h i n a q u a r i a v a r i e d d i u r n a l l y and s e a s o n a l l y , r a n g i n g from 9 to 1 9 ° C i n summer and from 8 to 1 1 ° C i n w i n t e r . Y a t e r from the s e t t l i n g pond c o n t a i n e d s m a l l numbers of i n v e r t e b r a t e s (mainly c h i r o n o m i d l a r v a e ) which c o u l d d r i f t through i n t a k e screens i n t o h o l d i n g a q u a r i a and be eaten by t r o u t . B e f o r e experiments w i t h p r e v i o u s l y unfed t r o u t , the water system was c l e a n e d at l e a s t once every two d a y s , r e d u c i n g the l i k e l i h o o d of such f e e d i n g . The i n c i d e n t l i g h t i n t e n s i t y ranged from 10 to 30 f t - c , which i s above the t h r e s h o l d f o r maximum f e e d i n g r a t e i n young salmon ( A l i , 1959; B r e t t and G r o o t , 1 963). The p h o t o p e r i o d was a d j u s t e d so t h a t i t was a p p r o x i m a t e l y normal f o r the season of the y e a r . T r a i n i n g and t e s t i n g foods Two t r a i n i n g and t e s t i n g foods were used i n many e x p e r -i m e n t s : t u b i f e x (common name) and b r i n e shr imp. The t u b i f e x , T u b i f e x s p . , were c o l l e c t e d from M a r s h a l l Creek, B. C. (49 122 S E ) . The b r i n e shr imp, A r t e m i a s a l i n a ( L i n n a e u s ) , were a d u l t animals o b t a i n e d c o m m e r c i a l l y ( f r o z e n : L o n g l i f e F i s h Food P r o d u c t s , S t e r n c o , H a r r i s o n , N. J . , USA; l i v e : C a l i f o r n i a B r i n e Shrimp C o . , Menlo P a r k , C a l i f . , USA) . F o r experiments 62 w i t h dead organisms, a l l were k i l l e d by f r e e z i n g . W i t h i n exper iments , the foods were removed as needed from s tocks prepared i n i t i a l l y . Because f r o z e n b l o c k s of t u b i f e x and b r i n e shrimp had been broken a p a r t , these foods c o n s i s t e d of p i e c e s as w e l l as whole o r g a n i s m s . T a b l e II p r e s e n t s the s i z e d i s t r i b u t i o n s of t u b i f e x and b r i n e shrimp used i n one experiment , but the d i s t r i b u t i o n s are r e p r e s e n t a t i v e of a l l exper iments . A l t h o u g h the two foods were s i m i l a r i n s i z e , the t u b i f e x were s l i g h t l y longer and the b r i n e shrimp w i d e r . Other experiments used mayf ly l a r v a e (or n a i a d s — E p h e m -e r o p t e r a ) , daphnia (Daphnia s p . ) , and u n s o r t e d p l a n k t o n ( m a i n l y c l a d o c e r a ) . The m a y f l y l a r v a e used were 2 to 5 mm t o t a l l e n g t h and were c o l l e c t e d from M a r s h a l l C r e e k . The daphnia used were 1 to 2 mm l o n g and were c u l t u r e d w i t h a l g a e . The l i v e p l a n k t o n was f r e s h l y c o l l e c t e d from a pond. F o r some t e s t s , these organisms were k i l l e d . U n l i k e t u b i f e x and b r i n e shr imp, they were not broken apar t w h i l e f r o z e n , so were i n t a c t organisms. Daphnia and mayf ly l a r v a e were always presented i n the r a t i o 3:2 because p r e l i m i n a r y o b s e r v -a t i o n s i n d i c a t e d t h a t young t r o u t would consume t h a t r a t i o when each food was p r e s e n t e d a l o n e . The h a t c h e r y food used i n t r a i n i n g experiments was a commercial product ( J . R. C l a r k C o . , S a l t Lake C i t y , U t a h , USA) . A d i f f e r e n t brand was used to t e s t t r o u t i n p a r e n t a l s t o c k experiments because t h e i r parents had been r e a r e d on i t ( S i l v e r Cup, Murray E l e v a t o r s , M u r r a y , U t a h ) . Both foods were 40 to 55% p r o t e i n , and t h e i r major c o n s t i t u e n t s were: 63 TABLE I I . S i z e d i s t r i b u t i o n of t u b i f e x and b r i n e shrimp used i n Experiment 7. Each d i s t r i b u t i o n i s based on t h r e e counts of about 500 p i e c e s of f o o d . T o t a l Length of Food (mm) 0 . 1 - 3 . 0 3 . 1 - 6 . 0 6 . 1 - 9 . 0 9 .1 -12 .0 9 .1 -50 .0 TUBIFEX Mean per cent per s i z e c l a s s 85.5 5.1 2.6 6.7 Standard e r r o r 0.33 0.55 0.19 0.94 Mean maximum w i d t h (mm) 0.420 0.442 0.444 0.483 Standard e r r o r 0.0236 0.0303 0.1325 0.0317 Number measured 22 20 15 20 BRINE SHRIMP Mean per cent per s i z e c l a s s 93.9 4 .9 0.9 0.2 S t a n d a r d e r r o r 0.58 0.31 0.23 0.05 Mean maximum w i d t h (mm) 0.870 2.542 3.597 4.627 Standard e r r o r 0.1027 0.1643 0.2778 0.3122 Number measured 41 31 12 10 64 f i s h meal , l i v e s t o c k o f f a l , and f l o u r e n r i c h e d w i t h v i t a m i n and m i n e r a l supplements . T r a i n i n g procedure T r a i n i n g c o n s i s t e d of f e e d i n g the t r o u t a s p e c i f i c food or s e r i e s of foods f o r a p e r i o d of t i m e . In a l l experiments but one (6 ) , the t r o u t were f e d o n l y t r a i n i n g f o o d ( s ) u n t i l b e i n g t e s t e d . Pood was u s u a l l y i n t r o d u c e d near the bottom of the c o n t a i n e r to c o n d i t i o n t r o u t to f e e d t h e r e . They f e d more r e a d i l y , however, when food was i n t r o d u c e d at the s u r f a c e and a l l o w e d to s i n k . When the f i s h were young, t h e r e f o r e , food was i n t r o d u c e d at the s u r f a c e f o r about 12 meals to f a c i l i -t a t e f e e d i n g . Amount of t r a i n i n g was the number of t r a i n i n g meals g i v e n a l l f i s h of an experiment . D u r i n g a t r a i n i n g meal , the f i s h i n each t reatment were o f f e r e d more f o o d than they would eat i n an hour once a day. In some experiments (1, 4, 5, 6, 8, 9 ) , there were a few days when the f i s h were not f e d . M o r t a l i t y d u r i n g t r a i n i n g was u s u a l l y 10 to 15% f o r a p e r i o d of 75 meals . Three k i n d s of c o n t a i n e r s were used i n the exper iments . Most t r o u t were t r a i n e d i n groups of at l e a s t 25 w i t h i n l a r g e a q u a r i a (25 by 50 cm f i l l e d 25 cm deep) . Water s p l a s h e d i n t o the a q u a r i a at one end and f l o w e d out through a s i p h o n (17 cm above the bottom) at the o t h e r . T r o u t t r a i n e d i n l a r g e a q u a r i a were u s u a l l y t e s t e d i n s m a l l a q u a r i a (21 by 35 cm, depth 7 cm u n l e s s s p e c i f i e d ) . I n two exper iments , f i s h were t r a i n e d i n p l a s t i c ( p o l y e t h y l e n e ) c o n t a i n e r s (9 by 9 cm, f i l l e d 65 6 cm d e e p ) . Twelve p l a s t i c c o n t a i n e r s were set i n t o a t r o u g h w i t h water f l o w i n g (250 ml /min) through h o l e s i n the s i d e of each. Such f i s h were t e s t e d i n p l a s t i c c o n t a i n e r s w i t h i n t a c t s i d e s . T e s t i n g procedure One to 24 hr b e f o r e a t e s t , t r o u t were moved from t h e i r t r a i n i n g c o n t a i n e r s to v i s u a l l y - i s o l a t e d t e s t i n g c o n t a i n e r s . O l d e r t r o u t were moved to the t e s t i n g c o n t a i n e r sooner than younger ones because o l d e r t r o u t r e q u i r e d more time i n the new s i t u a t i o n b e f o r e they would f e e d . B e i n g a lone seemed to d i s t u r b the o l d e r t r o u t more than b e i n g h a n d l e d or b e i n g i n a new c o n t a i n e r . I n a l l but two experiments (6 and 13) , each t r o u t was t e s t e d i n a separa te c o n t a i n e r . Y a t e r d i d not f l o w through c o n t a i n e r s d u r i n g a t e s t . In t e s t s w i t h t u b i f e x and b r i n e shr imp, the d e n s i t i e s of f o o d o f f e r e d each t r o u t were a p p r o x i m a t e l y e q u a l . The d e n s i t y of each f o o d was 20 times g r e a t e r than any t r o u t a t e . Both foods were i n t r o d u c e d s i m u l t a n e o u s l y on the bottom of the c o n t a i n e r and i n separa te areas ( p e r i m e t e r s about 3 cm a p a r t ) . T r o u t u s u a l l y began f e e d i n g w i t h i n 30 sec a f t e r the food was i n t r o d u c e d . The i n t e n s i t y of f e e d i n g decreased markedly w i t h t i m e , and the f r e q u e n c y of r e j e c t i n g f o o d i n c r e a s e d . D u r i n g 10-min f e e d i n g s e s s i o n s , 50$ of the t o t a l number of f o o d items was eaten w i t h i n 2.5 min, and 75$ w i t h i n 5 m i n . C o n s e q u e n t l y , , a 5-min t e s t p e r i o d was adopted f o r most e x p e r i m e n t s . I n most t e s t s w i t h t u b i f e x and shrimp, the number of 66 t imes a t r o u t ate each f o o d was counted . Vhen the k i n d eaten was i n doubt ( l e s s than 2$) , no count was r e c o r d e d f o r e i t h e r f o o d . Food s t r u c k but l a t e r r e j e c t e d was t a l l i e d s e p a r a t e l y . Experiments w i t h two observers used complete b l o c k d e s i g n s . I n some exper iments , the p i e c e s of f o o d i n stomachs were counted a f t e r f e e d i n g . Such data, were not e q u i v a l e n t to that o b t a i n e d i n 5-min o b s e r v a t i o n s because f i s h sometimes ate s e v e r a l p i e c e s at once and because they may have f u r t h e r fragmented the p i e c e s . U n l e s s s p e c i f i e d o t h e r w i s e , a l l f i s h were s t a r v e d f o r 48 h r b e f o r e a t e s t and 24 h r between c o n s e c -u t i v e t e s t s . The t e s t s w i t h m a y f l y l a r v a e , d a p h n i a , and h a t c h e r y food l a s t e d 3 hr as d i d those w i t h l i v e and dead p l a n k t o n ( E x p e r -iments 9, 11, and 13) . They were performed i n s m a l l a q u a r i a w i t h dead foods d i s p e r s e d e v e n l y on the bottom. A l l these t r o u t were s t a r v e d f o r at l e a s t . 4 8 hr b e f o r e t e s t i n g . A f t e r these exper iments , the t r o u t were k i l l e d and p r e s e r v e d i n 10$ f o r m a l i n ; l a t e r they were d i s s e c t e d and t h e i r food was counted . A n a l y s i s The r e s u l t s were a n a l y z e d i n two ways which have p o t e n -t i a l l y d i f f e r e n t b i o l o g i c a l meanings. The f i r s t methods of a n a l y s i s gave equal weight to the response of each i n d i v i d u a l r e g a r d l e s s of amount ea ten . The second method p o o l e d the food of a l l i n d i v i d u a l s w i t h i n a t r e a t m e n t , so gave more weight to i n d i v i d u a l s which had eaten more. The advantage of t o t a l i n g 67 the f o o d eaten was an i n c r e a s e d s e n s i t i v i t y to t reatment e f f e c t s , r e s u l t i n g from a l a r g e r sample s i z e . However, u n l e s s f i s h w i t h more food, s e l e c t e d i t the same way as those w i t h l e s s , the c o n c l u s i o n s would not a p p l y to a random sample of i n d i v i d u a l s . The assumption t h a t s e l e c t i o n was independent of t o t a l amount eaten was found to be warranted i n one impor tant case ( c o r r e l a t i o n c o e f f i c i e n t r = 0 .030, 180 d f ; da ta of T a b l e I V : 4-7 and Table I X ) . I n s p e c t i o n of the o ther experiments suggested o n l y one, noted i n the t e x t , i n which t o t a l food s e l e c t i o n d i d not correspond w i t h s e l e c t i o n by the average f i s h . 68 RESULTS PART I E f f e c t s of F e e d i n g H i s t o r y on Food S e l e c t i o n T r a i n i n g on dead t u b i f e x and b r i n e shrimp S e v e r a l experiments were undertaken to f i n d out whether t r o u t d e v e l o p t r a i n i n g b i a s e s and each had s l i g h t l y d i f f e r e n t m a t e r i a l s and methods as d e s c r i b e d i n T a b l e I I I and the t e x t . Data on some i n d i v i d u a l s are p r e s e n t e d i n more than one t a b l e or f i g u r e (Table I I I ) . F i g u r e 1 p r e s e n t s the combined r e s u l t s of a l l experiments u s i n g dead t u b i f e x and b r i n e shrimp as t r a i n i n g f o o d s , and T a b l e IV p r e s e n t s r e s u l t s f o r each experiment s e p a r a t e l y . Both show t h a t rainbow t r o u t developed t r a i n i n g b i a s e s . T h i s was t r u e i n a l l but Exper iment 3 (Table I V ) . A l l the data from t h i s experiment and a s i m i l a r one are p r e s e n t e d i n Table V . T a b l e V conf i rms t h a t t r o u t i n Experiment 3 d i d not show t r a i n i n g b i a s e s whereas those i n Experiment 2 d i d show them. The o n l y p r o c e d u r a l d i f f e r e n c e s between the two experiments was the number of i n d i v i d u a l s t r a i n e d i n a c o n -t a i n e r (Table I I I ) . In a l l experiments u s i n g two s t o c k s of t r o u t , the data were homogeneous between s tocks and t h e r e f o r e combined (Table I V ) . Hatchery f o o d was i n c l u d e d w i t h the t r a i n i n g foods i n Experiment 5 to e l i m i n a t e any e f f e c t of p o s s i b l e n u t r i -t i o n a l d e f i c i e n c i e s . No d e f i c i e n c i e s were apparent as the r e s u l t s were s i m i l a r to o t h e r s . Experiment 6 d i f f e r e d from the r e s t i n three r e s p e c t s . The t r o u t had been f e d h a t c h e r y TABLE I I I . D e s c r i p t i o n of a l l experiments u s i n g dead t u b i f e x and b r i n e shrimp as t r a i n i n g f o o d s . Except f o r those of Experiment 6, a l l t r o u t had eaten o n l y t h e i r t r a i n i n g f o o d ( s ) b e f o r e the t e s t meals. E x p t . Time S t o c k No. Type of Number of Trout Observer (s) Unusual T a b l e s and F i g u r e s No. of E x p t . of T r o u t T r a i n -i n g Meals T r a i n i n g C o n t a i n e r T r a i n e d per C o n t a i n e r Observed per T r a i n i n g Food P r o c e d - P r e s e n t i n g Data on: ure T S i m i l a r Same I n d i v ' l s I n d i v ' l s 1 Feb-Mar 1969 domestic 12 l a r g e a q u a r i a 60 10 Bryan t e s t s i n p l a s t i c c o n t a i n -ers none IV, VI 1 2 J u l y - A u g 1969 d o m e s t i c * w i l d * * 45 p l a s t i c c o n t a i n e r 1 8 B r y a n , Maurer t e s t s d u r i n g t r a i n i n g none I V , V, VI 1 3 J u l y - A u g 1969 dome s t i c * w i l d * * 45 p l a s t i c c o n t a i n e r 3 12 B r y a n , Maurer t e s t s d u r i n g t r a i n i n g none IV, V, VI 1 4 J u l y - S e p 1969 d o m e s t i c * w i l d * * 75 l a r g e a q u a r i a 50 1 2 B r y a n , ¥ o n g none none I V , V I , X, X I I I 1, 2 5 Oct -Dec 1969 w i l d 75 l a r g e a q u a r i a 30 12 B r y a n , ¥ o n g h a t c h e r y food + t r a i n i n g food VII I V , V I , X, X I , XI I I 1, 2 6 F e b r u a r y 1 970 d o m e s t i c * 14 l a r g e a q u a r i a 60 16 Bryan see t e x t none I V , VI 7 J u l y 1970 w i l d 9 l a r g e a q u a r i a 1 50 12 Bryan none IX, X, I V , V I , X I I , XI I I X, 2 , 3 1 , 2 * and * * i n d i c a t e t r o u t r e a r e d from the same b a t c h of eggs. t s i m i l a r means t h a t the i n d i v i d u a l s hatched from the same b a t c h of eggs and were t r a i n e d s i m u l t a n e o u s l y . FIGURE 1 . P r o p o r t i o n of t u b i f e x eaten by t r o u t o f f e r e d both t u b i f e x and b r i n e shrimp a f t e r t r a i n i n g on d i f f e r e n t f o o d ( s ) . S t r i p e d bars i n d i c a t e standard e r r o r s ; numbers above the a b s c i s s a are numbers of t r o u t which ate any food d u r i n g a choice t e s t . < g > Q Z CC 111 C L X LLJ U_ C O I D 60.0 40.0 z 111 o cc LU CL LU O < CC LU 20.0 3 t u b i f e x 69 b r i n e s h r i m p 60 h a t c h e r y f o o d TRAINING. 21 t u b i f e x & s h r i m p FOOD TABLE I V . Food s e l e c t e d by t r o u t g i v e n a choice between dead t u b i f e x and b r i n e shrimp a f t e r t r a i n i n g w i t h the same f o o d ( s ) f o r at l e a s t 9 meals . The data are the t o t a l number of p i e c e s eaten by a l l f i s h i n t h e i r f i r s t t e s t meal . Dashes i n d i c a t e o m i s s i o n of a treatment from an experiment . DATA ANALYSES TRAINING FOOD (TREATMENT) No. T u b i f e x (A) B r i n e Shrimp (B) Hatchery Food (C) T u b i f e x + Shrimp (D) None (E) Treatment Comparison C h i Square df No, Tub Eaten . S h r . No. Tub. Eaten Shr . No. Tub. Eaten Shr . No. Eaten Tub. Shr . No. Ea ten Tub. S h r . Value 1 42 14 18 38 23 24 - 14 15 A , B A , B, C A , B, E 18.99 20.90 20.88 1 2 2 .001 .001 .001 2 7 1 0 9 6 5 - - A , B A , B, C 10.02 13.52 1 2 .002 .002 3 7 21 57 24 27 30 - - - A , B A , B, C 13.62 16.32 1 2 .001 .001 4 37 14 38 64 19 28 - - A , B A , B, C 15.56 1 8.07 1 2 .001 .001 5 46 9 5 23 5 15 36 22 A , B A , B, C A , B, D 31 .17 40.99 33.98 1 2 2 .001 .001 .001 6 223 135 92 253 33 126 - - A , B A , B, C 88.72 123.78 1 2 .001 .001 7 48 30 35 53 82 97 32 47 33 40 A , B A , B, C A , B , D A , B, E 6.99 8.46 9.80 8.31 1 2 2 2 .008 .015 .008 .016 72 TABLE V . Food chosen by the t r o u t of Experiments 2 and 3 which were t r a i n e d s i n g l y and i n groups of three w i t h i n p l a s t i c c o n t a i n e r s . These t r o u t were t e s t e d d u r i n g t r a i n i n g , and the schedule of t r a i n -i n g and t e s t i n g meals was: 3, 1; 6, 2; 12, 2; 24, 2. The data are t o t a l number of p i e c e s eaten by a l l i n d i v i d u a l s i n a l l t e s t s . TRAINING FOOD (TREATMENTF T u b i f e x B r i n e Hatchery (A) Shrimp (B) Food (C) No. E a t e n No. E a t e n No. E a t e n Tub. S h r . Tub. S h r . Tub. S h r . E x p t . No. Treatment C h i df Comparison Square Value P< 77 31 37 63 48 30 A , B A , B, C 23.29 25.91 1 2 .001 .001 3 144 98 186 153 121 141 A , B 1 .05 1 .305 A , B, C 9.40 2 .010 73 food f o r about 7 months p r i o r to t r a i n i n g . H a l f of them were t e s t e d s i n g l y and h a l f i n groups of 4. The food data were o b t a i n e d by stomach f l u s h i n g a f t e r a 2 -hr t e s t . Experiment 6 was des igned to f i n d out whether f i s h t e s t e d s i n g l y showed more t r a i n i n g b i a s than those t e s t e d i n g r o u p s . They d i d n o t , so the data were p o o l e d . The food eaten by t r o u t i n the same treatment but d i f f e r -ent experiments shows some p e r p l e x i n g i n c o n s i s t e n c i e s (Table I V ) . The degree of food s e l e c t i o n by t r o u t i n c o n t r o l s (C, D , E ) was u s u a l l y i n t e r m e d i a t e between those i n other t r e a t -ments ( A , B ) . A l l c o n t r o l s were s i m i l a r when the t r o u t were young and had l i t t l e t r a i n i n g (Table I V : 1, 7 ) . O l d e r t r o u t seemed to need exper ience w i t h t u b i f e x b e f o r e they would eat much of i t , as those t r a i n e d on h a t c h e r y food f o r more than 6 meals u s u a l l y s e l e c t e d shrimp (Table I V : 4 , 5 , 6 ) . F u r t h e r g e n e r a l i z a t i o n i s tenuous . D i f f e r e n t c o n t r o l s were not always homogeneous w i t h i n an experiment (Table I V : 5) . C o n -t r o l s C and D were heterogeneous i n d i f f e r e n t exper iments . D e s p i t e these i n c o n s i s t e n c i e s , the data i n d i c a t e t h a t both foods were at l e a s t a c c e p t a b l e to t r o u t . F o r a l l t reatments ( A , B , C , D , E ) , the p r o p o r t i o n of i n d i v i d u a l s which ate b o t h foods d u r i n g a t e s t ranged from 52 to 57$. As d i s c u s s e d p r e v i o u s l y , the experiments can be a n a l y z e d i n a l e s s p o w e r f u l way by u s i n g responses of i n d i v i d u a l s . T a b l e VI p r e s e n t s such an a n a l y s i s f o r Experiments 1 to 7, and shows the t r a i n i n g e f f e c t . The data were not o r t h o g o n a l because d i f f e r e n t numbers of t r o u t were used i n d i f f e r e n t 74 TABLE V I . E f f e c t of t r a i n i n g on the p r o p o r t i o n of t u b i f e x ( a r c s i n e per cent f o r each i n d i v i d u a l ) eaten i n the f i r s t meal a f t e r t r a i n i n g . The data are from Experiments 1 to 7, but o n l y the t u b i f e x , b r i n e shr imp, and h a t c h e r y food t reatments are i n c l u d e d i n the a n a l y s i s . Source of V a r i a t i o n df Mean Square F p <; T r a i n i n g foods (TF) E a d j u s t e d f o r TF 2 6 9223.85 946.79 13.65 1 .40 .001 .25 TF a d j u s t e d f o r E "Experiments (E) 2 6 9474.28 863.32 14.02 1 .28 .001 .50 I n t e r a c t i o n Remainder 12 181 2518.22 675.54 3.73 .001 75 experiments and because some t r o u t d i d not f e e d . A n a l y s i s of nonor thogonal data i s d i s c u s s e d by S t e e l and T o r r i e (1960). There were no s i g n i f i c a n t d i f f e r e n c e s among experiments (Table V I : E and E a d j u s t e d f o r T F ) . However, t h e r e was i n t e r a c t i o n among Experiments and T r a i n i n g Foods . Such i n t e r a c t i o n seems r e a s o n a b l e i n t h i s s i t u a t i o n , ( i . e. i t would be unusual i f the same c o n s t a n t , r e p r e s e n t i n g per cent t u b i f e x , c o u l d be f i t t e d to each t reatment w i t h i n experiments because two t r e a t -ments were expected to d i f f e r i n o p p o s i t e d i r e c t i o n s ) . The e f f e c t of t r a i n i n g food (Table V I : TF and TF a d j u s t e d f o r E) was l a r g e r e l a t i v e to e i t h e r i n t e r a c t i o n or r e m a i n d e r . Thus , a n a l y s i s of v a r i a n c e a l s o showed t h a t the t reatments d i f f e r e d , and data i n s p e c t i o n showed t h a t t r o u t s e l e c t e d f a m i l i a r f o o d . T r a i n i n g b i a s w i t h l i v e food Experiment 8 was under taken to see whether t r a i n i n g b i a s e s c o u l d be produced u s i n g l i v e f o o d . As t u b i f e x was the o n l y l i v e food c o n t i n u o u s l y a v a i l a b l e , Experiment 8 c o n s i s t e d of a l i v e t u b i f e x treatment and a h a t c h e r y food c o n t r o l . Because of c o s t , o n l y one shipment of b r i n e shrimp was u s e d ; as most shrimp d i e d w i t h i n a week, they were used f o r t e s t i n g but noit t r a i n i n g . The locomotory b e h a v i o r and v e r t i c a l d i s t r i b u t i o n s of the two prey d i f f e r e d . The t u b i f e x were l o c a t e d on the bottom, u n d u l a t i n g or c r a w l i n g v e r y s l o w l y . The shrimp were d i s t r i b u t e d m a i n l y near the bot tom, but about one q u a r t e r were always swimming between the s u r f a c e and the 76 bottom. A l l shrimp moved h o r i z o n t a l l y , and much f a s t e r than the t u b i f e x . Table V I I i n d i c a t e s t h a t t r o u t i n both t reatments s e l -ec ted l i v e b r i n e shrimp r e l a t i v e to l i v e t u b i f e x . The same i n d i v i d u a l s were observed i n t e s t meals 1 to 3, and r e s u l t s f o r a l l t e s t s w i t h l i v e f o o d were homogeneous. A f t e r three t e s t meals of l i v e f o o d , b o t h groups were f e d 6 meals of h a t c h e r y food b e f o r e the t e s t w i t h dead f o o d . In t h i s t e s t , i t was n e c e s s a r y to s u b s t i t u t e f i s h (3 per t reatment) not t e s t e d p r e v i o u s l y because some had escaped when t h e i r tank o v e r f l o w e d . Y i t h dead t e s t f o o d , the t r o u t t r a i n e d on t u b i f e x s e l e c t e d t u b i f e x r e l a t i v e to those t r a i n e d on h a t c h e r y food (Table V I I : Meal 4 ) . The data f o r t r o u t t r a i n e d on h a t c h e r y f o o d can be used to determine whether the two t e s t foods were eaten i n the same p r o p o r t i o n whether a l i v e or dead . Yhen the t o t a l amount of l i v e food (Table V I I : Meals 1-3) was compared w i t h dead food 2 (Meal 4 ) , the two were heterogeneous (X = 14 .7 , 1 df , p < 0 .001) . Thus , the t r o u t had s e l e c t e d an even g r e a t e r p r o p o r t i o n of b r i n e shrimp when both foods were a l a v e than when b o t h were dead. The same r e s u l t was o b t a i n e d w i t h other t r o u t a l s o t r a i n e d on h a t c h e r y food but t e s t e d f i r s t w i t h dead foods then w i t h l i v e foods ( X 2 = 4 . 4 , 1 df - , p < 0 .034) . P r e l i m i n a r y o b s e r v a t i o n s w i t h a t r e a t m e n t , but no c o n t r o l , a l s o i n d i c a t e d t h a t t r a i n i n g b i a s e s were not always expressed i n t e s t s w i t h l i v e f o o d . Trout t r a i n e d on l i v i n g , s m a l l e r t r o u t s e l e c t e d t r o u t when t e s t e d w i t h dead foods but not always 77 TABLE V I I . Number of t u b i f e x and b r i n e shrimp eaten by a l l t r o u t t r a i n e d on l i v e t u b i f e x f o r 75 meals then t e s t e d w i t h l i v e and dead f o o d . The t e s t s w i t h l i v e food used 50 t u b i f e x and 50 b r i n e shr imp, whereas those w i t h dead food used the u s u a l p r o -cedure . Tes t Nature TRAINING FOOD Meal of T e s t L i v e T u b i f e x Hatchery Food C h i df p < No. Foods No. Eaten No. E a t e n Square Tub. S h r . Tub. S h r . Value 1 A l i v e 6 49 28 35 14. 51 1 .001 2 A l i v e 13 84 15 65 .58 1 .452 3 A l i v e 13 93 17 75 1 .04 1 .310 4 Dead 76 18 44 47 20.03 1 .001 78 when t e s t e d w i t h l i v e f o o d s . The t e s t foods were: t r o u t , amphipods, c o r i x i d s , and m a y f l y l a r v a e . T r a i n i n g b i a s e s w i t h other foods S i n c e most experiments used the same f o o d s , i t i s i m p o r -t a n t to know whether the r e s u l t s can be g e n e r a l i z e d to other f o o d s . I n Experiment 9, t r o u t were t r a i n e d on daphnia or m a y f l y l a r v a e . They were f e d l i v e t r a i n i n g food from h a t c h i n g u n t i l t e s t i n g but were t e s t e d with dead organisms o n l y (August 1968). Those t r a i n e d on mayf ly l a r v a e r e c e i v e d 20 t r a i n i n g meals whereas the others r e c e i v e d 30. Those t r a i n e d on daphnia r e c e i v e d m a i n l y d a p h n i a , but some other p l a n k t o n was i n c l u d e d . T a b l e V I I I shows t h a t t r o u t t r a i n e d on e i t h e r mayf ly l a r v a e or daphnia s e l e c t e d t h e i r t r a i n i n g f o o d . S e l e c t i o n f o r t r a i n i n g food was a l s o observed i n three se ts of o b s e r v a -t i o n s w i t h a t reatment but no c o n t r o l . As d e s c r i b e d p r e v i o u s l y , t r o u t t r a i n e d on s m a l l e r t r o u t s e l e c t e d them when t e s t e d w i t h dead f o o d s . Those t r a i n e d on f r u i t f l i e s s e l e c t e d f l i e s r e l -a t i v e to t u b i f e x . Other t r o u t t r a i n e d on h a t c h e r y food s e l e c t -ed i t r e l a t i v e to dead b r i n e shrimp i n t e s t 1; however, they s e l e c t e d n e i t h e r f o o d i n t e s t 2 and s e l e c t e d b r i n e shrimp i n t e s t s 3 to 7. S a t i a t i o n and degree of t r a i n i n g b i a s To determine whether the p r o p o r t i o n of t r a i n i n g f o o d eaten changes d u r i n g a meal , I k e p t separate r e c o r d s of the f o o d eaten i n the f i r s t and second h a l f of a t e s t meal . These data were then analyzed f o r h e t e r o g e n e i t y to detect any 79 TABLE V I I I . Food eaten by t r o u t (8 per t reatment ) t r a i n e d on l i v e d a p h n i a , l i v e m a y f l y l a r v a e , or h a t c h e r y food and t e s t e d w i t h 30 dead daphnia and 20 dead m a y f l y l a r v a e . TRAINING FOOD Daphnia M a y f l y Larvae Hatchery Food C h i df p< No. E a t e n No. Eaten No. Eaten Square Daphnia Larvae Daphnia Larvae Daphnia Larvae Value 72 39 29 35 56 71 11.69 2 .004 80 change i n food s e l e c t i o n w i t h s a t i a t i o n . The term s a t i a t i o n does not i m p l y t h a t the f i s h were r e p l e t e i n the second h a l f of a t e s t , o n l y that they a t e l e s s (25% t o t a l ) . The method of a n a l y s i s was to conver t the number of the two k i n d s of food eaten by each t r o u t i n t o a s i n g l e d e v i a t e : (n t u b i f e x - n s h r i m p ) / " V ( r r t u b i f e x + n s h r i m p ) . The expected mean of the d e v i a t e s i s zero i f t h e r e was no s e l e c t i o n . The d e v i a t e s were formed s e p a r a t e l y f o r food eaten i n the f i r s t , second, and b o t h h a l v e s o f the t e s t . H e t e r o g e n e i t y i n d i c a t e s whether a food was s e l e c t e d to a g r e a t e r ex tent i n the f i r s t than the second h a l f of a meal . The expected v a l u e s are zero i f no h e t e r o g e n e i t y , p o s i t i v e i f s e l e c t i o n f o r t u b i f e x , and n e g a t i v e i f s e l e c t i o n f o r b r i n e shr imp. The t e s t s f o r h e t e r o -g e n e i t y are s i g n e d v a l u e s pf "Vchi square , and the method was o u t l i n e d by Yates (1955a, 1955b). The a n a l y s i s , used o n l y f i s h which ate both foods and ate at l e a s t one k i n d i n each h a l f of the meal . T a b l e IX shows t h a t t r o u t w i t h a t r a i n i n g b i a s s e l e c t e d t h e i r t r a i n i n g food more s t r o n g l y i n the f i r s t than the second h a l f of a t e s t . Food d e p r i v a t i o n and degree of t r a i n i n g b i a s To f i n d out whether d e p r i v a t i o n time i n f l u e n c e d the degree of s e l e c t i o n f o r a t r a i n i n g f o o d , I used t r o u t which had been t r a i n e d f o r 12 meals and t h e n d e p r i v e d of food f o r a p p r o x i -mately 3, 24, 48, and 96 h r . At each d e p r i v a t i o n t i m e , 24 f i s h (12 per t reatment ) were t e s t e d . Both a n a l y s i s of v a r i a n c e of i n d i v i d u a l responses and c h i square a n a l y s i s of t o t a l food 81 TABLE IX. E f f e c t of s a t i a t i o n on t r a i n i n g b i a s . The data are means f o r response of i n d i v i d u a l s c o n v e r t e d to s i n g l e d e v i a t e s as d e s c r i b e d i n t e x t . P o s i t i v e v a l u e s i n d i c a t e s e l e c t i o n f o r t u b i f e x and n e g a t i v e v a l u e s s e l e c t i o n f o r b r i n e shr imp. P e r i o d When Food T r a i n i n g Food 1 - t a i l e d Was E a t e n T u b i f e x B r i n e Shrimp T p < F i r s t H a l f 1 .265 -0 .349 4.30 .001 Second H a l f 0.054 -0 .156 0.65 .50 E n t i r e Meal 1.115 -0 .344 3.92 .001 H e t e r o g e n e i t y (between f i r s t and second) 0.716 -0 .108 2.19 .025 Sample s i z e 29. 36. Average SE 0.276 0.234 82 i n d i c a t e d t h a t the data were homogeneous among d e p r i v a t i o n times and between t r a i n i n g f o o d s . Data i n s p e c t i o n r e v e a l e d no s imple t r e n d between f o o d d e p r i v a t i o n and food s e l e c t i o n . P r o p o r t i o n of t r a i n i n g and n o v e l food r e j e c t e d D u r i n g the t e s t meals , food s t r u c k but r e j e c t e d was r e c o r d e d as w e l l as food ea ten . Such data can be a n a l y z e d to determine whether n o v e l food was r e j e c t e d more f r e q u e n t l y than t r a i n i n g f o o d . The method was the same as i n the s a t i a t i o n exper iment . The a n a l y s i s used data f o r i n d i v i d u a l s t h a t d i d t h r e e t h i n g s : ate or r e j e c t e d both f o o d s , ate at l e a s t one k i n d , and r e j e c t e d at l e a s t one k i n d . H e t e r o g e n e i t y i n d i c a t e s whether foods were r e j e c t e d i n the same p r o p o r t i o n as they were eaten w i t h p o s i t i v e v a l u e s r e p r e s e n t i n g s e l e c t i v e e a t i n g of t u b i f e x . F o r example, a l a r g e p o s i t i v e v a l u e of h e t e r o g e n e i t y would i n d i c a t e t h a t t u b i f e x was eaten more f r e q u e n t l y than i t was r e j e c t e d , r e l a t i v e to the p r o p o r t i o n of shrimp eaten and rej e c t e d . The f i r s t row of Table X c o n f i r m s p r e v i o u s r e s u l t s by showing t h a t t r o u t s e l e c t i v e l y ate the f a m i l i a r food when f i r s t p r e s e n t e d w i t h two f o o d s . The second row shows t h a t t r o u t t r a i n e d on t u b i f e x tended to r e j e c t shrimp and those t r a i n e d on shrimp to r e j e c t t u b i f e x . T h i s i s shown more c l e a r l y by the measures of h e t e r o g e n e i t y , however. The two c o n t r o l groups ( t u b i f e x and shr imp, h a t c h e r y food) d i d not d i f f e r markedly from zero or from each o t h e r . In a l l t r e a t -ments, the two foods were examined w i t h a b o u t i h e same f r e q u e n c y . TABLE X. E f f e c t of t r a i n i n g on k i n d of food eaten and k i n d r e j e c t e d by t r o u t . Food of each f i s h was c o n v e r t e d to a s i n g l e d e v i a t e as i n T a b l e IX. P o s i t i v e v a l u e s i n d i c a t e s e l e c t i o n f o r t u b i f e x and n e g a t i v e v a l u e s s e l e c t i o n f o r b r i n e s h r i m p . TRAINING FOOD T u b i - B r i n e T u b i f e x and Hatchery RESPONSE TO TEST FOOD fex Shrimp B r i n e Shrimp Food Eaten Re j ec ted H e t e r o g e n e i t y between k i n d s eaten and r e -j ec ted Examined (eaten and r e j e c t e d ) Sample s i z e Average s tandard e r r o r +0/7.19** -0 .522** +0.144 -0 .142 +0.5-26* -0 .495* +0.543** -0 .826** +0.422 +0.413 +0.023 -0 .226 82 84 35 .1904 .1812 .2372 -0.321 +0.128 -0.385 -0 .185 40 .2650 * and * * i n d i c a t e p r o b a b i l i t i e s (0 .05 , 0 .01 ; 2 - t a i l e d ) of f o r t u i t o u s d i f f e r e n c e from z e r o . 84 Food s e l e c t i o n by i n d i v i d u a l s w i t h i n t reatments To f i n d out whether i n d i v i d u a l s w i t h i n t reatments tended to eat s i m i l a r food i n s u c c e s s i v e meals , t r o u t were t e s t e d f o r s e v e r a l meals a f t e r t r a i n i n g . O b s e r v a t i o n s of two a d d i t i o n a l meals were made on f i s h i n Experiments 4 and 5. A l l data f o r p a i r s of c o n s e c u t i v e meals were a n a l y z e d to see whether i n d i v -i d u a l s ate p r e d o m i n a n t l y the same food more o f t e n than expected by chance. I n d i v i d u a l s t r a i n e d on t u b i f e x , b r i n e shr imp, or h a t c h e r y food d i d n o t , whereas those t r a i n e d on both t u b i f e x and b r i n e shrimp d i d s e l e c t the same k i n d more o f t e n t h a n expected by chance. These f i s h were observed f o r a t o t a l of 7 meals each, and f u r t h e r a n a l y s i s i s p r e s e n t e d i n Table X I . Table XI shows t h a t the p r o p o r t i o n of t u b i f e x eaten was more c o n s i s t e n t f o r the same i n d i v i d u a l than f o r d i f f e r e n t i n d i v i d u a l s . D i f f e r e n c e among i n d i v i d u a l s (ITR and ITR a d -j u s t e d f o r Time I n t e r v a l s ) was l a r g e r e l a t i v e to e i t h e r remainder or i n t e r a c t i o n . The f i n d i n g t h a t i n t e r a c t i o n was i t s e l f l a r g e , r e l a t i v e to the remainder , i m p l i e s t h a t the i n d i v i d u a l s d i d change somewhat d u r i n g the unobserved meals . The e f f e c t of d i f f e r e n t t imes (TIME and TIME a d j u s t e d f o r ITR) was s m a l l , i n d i c a t i n g t h a t the p r o p o r t i o n eaten by a l l i n d i v -i d u a l s d i d not change. In other words, T a b l e XI shows t h a t the average i n d i v i d u a l c o n s i s t e n t l y ate a s i m i l a r p r o p o r t i o n of the two foods (Table I X ) . The d i f f e r e n c e s among the 12 i n d i v i d u a l s were not 85 TABLE X I . P r o p o r t i o n of t u b i f e x and b r i n e shrimp ( a r c s i n e per cent t u b i f e x ) eaten by i n d i v i d u a l t r o u t t r a i n e d on both foods f o r 75 meals b e f o r e the t e s t meals . The e n t i r e schedule of unobserved and observed meals was 7 5 , 3 ; 4 , 2 ; 4 , 2 . C o n s e c u t i v e t e s t s were used as r e p l i c a t e s . SOURCE OP VARIATION df Mean Square F P < I n d i v i d u a l T r o u t (ITR) 11 1745. 328 3 .96 .001 TIME A d j u s t e d f o r ITR 2 736. 196 1 .67 .25 ITR A d j u s t e d f o r TIME 11 1745. 898 3 .98 .001 Time I n t e r v a l s (TIME) 2 683. 560 1 .55 .25 I n t e r a c t i o n 22 824. 522 1 .87 .05 Remainder 46 441 . 299 86 extremely l a r g e . The two t r o u t which were the most " f o n d of t u b i f e x " averaged 72 and 80$ t u b i f e x . The two which were the most " f o n d of b r i n e shrimp" averaged 5 and 21$ t u b i f e x . A l l t r o u t i n a l l t e s t s averaged 49$ t u b i f e x . F u r t h e r t r a i n i n g on the o r i g i n a l f o o d Responses of t r o u t t r a i n e d f o r d i f f e r e n t d u r a t i o n s were compared to determine the extent of t r a i n i n g n e c e s s a r y f o r e x p r e s s i o n of t r a i n i n g b i a s e s and the e f f e c t of i n c r e a s e d t r a i n i n g . F i g u r e 2 shows t h a t t r o u t d i d not d e v e l o p a c o n s i s t -ent t r a i n i n g b i a s p r i o r to 6 t r a i n i n g meals . The c r i t e r i o n f o r t r a i n i n g b i a s was s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e among the t reatments i n p r o p o r t i o n o f t e s t foods eaten and s e l e c t i o n of f a m i l i a r f o o d . A t r a i n i n g b i a s was e v i d e n t a f t e r 9 meals (Table I V : 7 ) , but not a f t e r 6 meals . Other o b s e r v a t i o n s i n d i c a t e d t h a t 6 to 9 t r a i n i n g meals were r e q u i r e d f o r s i g n i f -i c a n t t r a i n i n g b i a s w i t h a sample s i z e of 12 f i s h . For i n s t a n c e , t r o u t t r a i n e d w i t h those i n Experiment 6 d i d not show b i a s e s a f t e r 7 t r a i n i n g meals ; o thers t r a i n e d w i t h those of Experiment 4 had developed t r a i n i n g b i a s e s a f t e r 9 meals . S i n c e the e f f e c t of t r a i n i n g was l i n e a r , r e g r e s s i o n a n a l -y s i s can be used to determine whether t r a i n i n g beyond the m i n -imum i n c r e a s e d the degree of b i a s . When d a t a f o r 12 to 75 meals were u s e d , the s lope f o r both t reatments combined was not s i g -FIGURE 2. E f f e c t of t r a i n i n g d u r a t i o n on the amount of t r a i n i n g food ea ten . P o i n t s i n d i c a t e means and l i n e s , s tandard e r r o r s . (The a r c s i n e of 50% i s 45 . ) 0 4-* CO 0 D O O cn c c D O E < c 0 O L _ 0 C L 5= o 0 c 0) o CO 80 60 40 20 • Tubifex A Brine shrimp 4 o 0 8 12 J I L 16 20 24 _ I L 72 76 Number of training meals n i f i c a n t l y d i f f e r e n t from z e r o . F i g u r e 2 suggests that the e f f e c t of t r a i n i n g was g r e a t e r f o r t u b i f e x ( s l o p e = 0.244, SE = 0.1170) than f o r b r i n e shrimp ( s l o p e = 0 .040, SE = 0 .1154) . However, I t h i n k t h i s d i f f e r e n c e was s p u r i o u s , not o n l y because the o v e r - a l l r e g r e s s i o n was i n s i g n i f i c a n t , but a l s o because other o b s e r v a t i o n s on the same or s i m i l a r l y t r a i n e d f i s h (12 and 75 meals) showed t reatment d i f f e r e n c e s i n o p p o s i t e d i r e c -t i o n s . A f t e r d e v e l o p i n g a b i a s , t r o u t ate about 70% t r a i n i n g food no matter how long they had been t r a i n e d , F u r t h e r t r a i n i n g on a n o v e l f o o d Experiment 10 was d e s i g n e d to determine which food t r o u t would s e l e c t when t r a i n e d on two foods i n s u c c e s s i o n . When t r o u t were t r a i n e d f i r s t on one f o o d and then on a n o t h e r , they s e l e c t e d the second t r a i n i n g food (Table X I I , F i g u r e 3 ) . The same data were a n a l y z e d to see which food was the f i r s t one eaten i n a t e s t . Seven t r o u t ate t h e i r f i r s t t r a i n i n g f o o d f i r s t , and 17 ate t h e i r second t r a i n i n g food f i r s t ( b i n o m i a l p< 0 .033) . The c o n t r o l s , i n i t i a l l y t r a i n e d on t u b i f e x or b r i n e shrimp and then on h a t c h e r y f o o d , r e t a i n e d the b i a s f o r t h e i r i n i t i a l t r a i n i n g food (Table X I I , F i g u r e 3 ) . F u r t h e r t r a i n i n g on both the o r i g i n a l and n o v e l foods The p r e v i o u s two s e c t i o n s have shown that t r a i n i n g b i a s e s were m a i n t a i n e d when the t r o u t c o n t i n u e d to eat the same food 89 TABLE XIIw Numbers of t u b i f e x and b r i n e shrimp eaten by t r o u t a f t e r t r a i n i n g on two foods i n s u c c e s s i o n (12 meals of each f o o d ) . The data are t o t a l s f o r the 12 t r o u t i n each t reatment . TRAINING FOODS F i r s t Second T u b i f e x B r i n e Shrimp T u b i f e x B r i n e Shrimp B r i n e Shrimp T u b i f e x Hatchery Food Hatchery Food NUMBER EATEN Treatment T u b i f e x Shrimp TS ST TH SH 27 62 60 41 41 16 27 82 TREATMENT COMPARISON TS w i t h ST TH w i t h SH TS w i t h TH ST w i t h SH CHI SQUARE VALUE df p.< 22.51 1 0.001 24.51 1 0.001 12.11 1 0.001 38.87 1 0.001 FIGURE 3 . P r o p o r t i o n of t u b i f e x eaten by a l l i n d i v i d u a l s a f t e r two s u c c e s s i v e t r a i n i n g 80 r z LU h -< L U x 60 L U L L 5 => 40 z L U 20 O D C L U C L p e r i o d s . The p e r i o d s l a s t e d 12 meals ; a f t e r the second p e r i o d the t r o u t were g i v e n a choice of t u b i f e x (T) and b r i n e shrimp ( S ) . H r e p r e s e n t s h a t c h e r y f o o d . n 1 s t FOOD: T T 2 n d FOOD: T H T S T S T+.S S TRAINING S S S H T T+S FOOD(S) H H T+S T+S 91 but a l t e r e d when they were f e d a new t r a i n i n g f o o d . I t i s r e l e v a n t , t h e r e f o r e , to know how long t r a i n i n g b i a s e s p e r s i s t when t r o u t are a l l o w e d to choose e i t h e r t h e i r t r a i n i n g food or a n o v e l f o o d . To determine t h i s time of v o l u n t a r y m a i n t e n -ance , f i s h of Experiments 4, 5, and 7 were f e d b o t h t e s t foods f o r a number of meals . In each meal , a l l t r o u t were f e d a p p r o x i m a t e l y equal d e n s i t i e s of the two f o o d s ; the d e n s i t y of each food was g r e a t e r than would be eaten i n one h o u r . Experiment 4 shows that the t r a i n i n g b i a s d i d not p e r s i s t f o r 75 meals , the o r i g i n a l t r a i n i n g p e r i o d (Table X I I I ) . In Experiment 5, a t r a i n i n g b i a s was e v i d e n t i n meals 9 and 14, but not i n 15. When the data f o r meals 14 and 15 were p o o l e d , there was no d i f f e r e n c e between the two t r e a t m e n t s . Thus , the t r a i n i n g b i a s e s d i s a p p e a r e d a f t e r 14 meals of both f o o d s . In Experiment 7, t r a i n i n g b i a s e s were e v i d e n t i n meal 18 but not i n 24 (Table X I I I , F i g u r e 3 ) . In meal 18, however, the t r a i n -i n g b i a s may have been weaker than i n d i c a t e d because one f i s h made an u n u s u a l l y great c o n t r i b u t i o n to the t o t a l . Without t h i s i n d i v i d u a l , the t reatments would not d i f f e r ; moreover , the average responses of i n d i v i d u a l s suggest t h a t there was no d i f f e r e n c e . T h i s experiment i n d i c a t e s t h a t t r a i n i n g b i a s e s p e r s i s t e d between 12 and 23 meals of b o t h f o o d s . The combined r e s u l t s of Experiments 5 and 7 i n d i c a t e t h a t b i a s e s were v o l -u n t a r i l y m a i n t a i n e d between 14 and 23 meals . T h i s i s r o u g h l y twice the number of meals r e q u i r e d to induce a b i a s . 92 TABLE X I I I . P e r s i s t e n c e of t r a i n i n g b i a s when t r o u t are a l l o w e d to eat both t e s t foods a f t e r the t r a i n i n g p e r i o d . The data are t o t a l food of 12 i n d i v i d u a l s per t r e a t -ment, and the same i n d i v i d u a l s were observed on s u c -c e s s i v e meals , w i t h i n exper iments . E x p t . No. of No. of No. T r a i n - Meals i n g With Meals Both Foods TRAINING FOOD C h i T u b i f e x  No. Ea ten Tub": Shr? B r i n e Shrimp Square JMo. E a t e n Value Tub. S h r . df p< 2 52 20 30 73 29.90 1 .001 3 34 1 6 1 5 57 25.39 1 .001 2+3 86 36 45 1 30 56.66 1 .001 76 6 25 13 13 4.68 1 .029 77 23 29 9 21 1 .08 1 .301 78 23 17 29 26 0.06 1 .789 76+77+78 52 71 51 60 0.19 1 .670 2 27 26 37 47 0 .37 1 .548 3 85 32 30 44 18.19 1 .001 2+3 112 58 67 91 17.27 1 .001 8 68 27 54 50 7.28 1 .007 9 41 28 22 56 13.32 1 .001 8+9 109 55 76 106 20.18 1 .001 14 28 27 8 32 8.13 1 .005 15 23 30 18 17 0.27 1 .609 14+1 5 51 57 26 49 2 .37 1 .120 6 66 33 25 62 25.17 1 .001 12 29 17 15 30 6.90 1 .009 18 69 35 34 48 10.50 1 .002 24 27 34 35 36 0.16 1 .690 93 DISCUSSION OF PART I The r e s u l t s i n d i c a t e t h a t t r a i n i n g b i a s e s can be produced i n rainbow t r o u t . B i a s e s developed i n r e c e n t l y hatched t r o u t which had eaten o n l y one food and i n o l d e r t r o u t which had eaten other foods b e f o r e t r a i n i n g . Y i t h dead f o o d , t r a i n i n g b i a s e s were always e v i d e n t when t r o u t were t r a i n e d i n l a r g e groups ( n > 2 5 ) w i t h i n l a r g e a q u a r i a (25 x 50 x 25 cm). B i a s e s a l s o d e v e l o p e d when t r o u t were t r a i n e d s i n g l y i n p l a s t i c c o n -t a i n e r s ( 9 x 9 x 6 cm). T r a i n i n g b i a s e s were not e v i d e n t , however, when t r o u t were t r a i n e d i n groups of t h r e e w i t h i n p l a s t i c c o n t a i n e r s . Some e f f e c t of group s i z e , c o n t a i n e r s i z e , or b o t h , presumably p r e v e n t e d e i t h e r development or e x p r e s s i o n of t r a i n i n g b i a s e s i n t h i s s i t u a t i o n . An experiment and p r e l i m i n a r y o b s e r v a t i o n s showed t h a t t r a i n i n g b i a s e s develop f o r a number of d i f f e r e n t f o o d s . No foods were found f o r which t r o u t d i d not develop a t r a i n i n g b i a s , but b i a s e s f o r some foods may have been stronger than f o r o t h e r s . A t r a i n i n g b i a s f o r h a t c h e r y food l a s t e d o n l y one meal . I t i s i m p o r t a n t t h a t a l l foods seemed a c c e p t a b l e to t r o u t . Because , i n other a n i m a l s , whether a t r a i n i n g b i a s developed and the degree of b i a s depended upon the type of t r a i n i n g foods ( T a b l e I ) . Yhen t r a i n e d on l i v e f o o d , t r o u t d i d not always s e l e c t f a m i l i a r food when t e s t e d w i t h l i v e f o o d s , but d i d when t e s t e d 94 w i t h dead f o o d s . In the l i v e t u b i f e x experiment , an e x p l a n a -t i o n f o r the l a c k of t r a i n i n g b i a s w i t h l i v e food was suggested by o b s e r v a t i o n of t r o u t i n e x p e r i e n c e d w i t h e i t h e r t u b i f e x or b r i n e shr imp. They s e l e c t e d b r i n e shrimp r e l a t i v e to t u b i f e x but i n much g r e a t e r p r o p o r t i o n when b o t h foods were a l i v e . Thus , when b o t h were a l i v e , b r i n e shrimp was much more l i k e l y to be a t t a c k e d than t u b i f e x , and t r a i n i n g d i d not i n c r e a s e the p r o b -a b i l i t y of e a t i n g t u b i f e x . The reason t h a t t r o u t t r a i n e d on s m a l l e r t r o u t d i d not always s e l e c t f a m i l i a r food when t e s t e d w i t h l i v e foods seemed to be t h a t the o t h e r foods were more e a s i l y c a p t u r e d . Had the p r o b a b i l i t i e s of b e i n g a t t a c k e d and c a p t u r e d been more equal f o r the l i v e foods I used , t r a i n i n g b i a s e s would p r o b a b l y have been e x p r e s s e d . When t r a i n e d and t e s t e d w i t h l i v e f o o d s , young salmon showed t r a i n i n g b i a s e s f o r two of three foods used ( L e B r a s s e u r , 1969). A number of animals s e l e c t p r e f e r r e d foods to d i f f e r e n t degrees depending on t h e i r hunger l e v e l . The u s u a l g e n e r a l -i z a t i o n i s t h a t animals are l e s s s e l e c t i v e when v e r y hungry ( I v l e v , 1961; Hafez and S c h e i n , 1962; Beukema, 1968). As o thers have p o i n t e d out , hunger i s d i f f i c u l t to d e f i n e i n a way which i s g e n e r a l , y e t m e a n i n g f u l , because d i f f e r e n t measures of hunger have d i f f e r e n t c h a r a c t e r i s t i c s ( B a r n e t t , 1963; de R u i t e r , 1967; M a r l e r and H a m i l t o n , 1966). S i m i l a r problems a r i s e i n d e f i n i n g f o o d p r e f e r e n c e s , p a r t i c u l a r l y as the word p r e f e r e n c e has many shades of meaning. C o n s e q u e n t l y , i t i s important to use the terms w i t h r e f e r e n c e to s p e c i f i c c i r c u m -stances and to r e c o g n i z e t h a t they may a p p l y o n l y to other s i t u a t i o n s which are v e r y s i m i l a r . On -their f i r s t encounter w i t h b o t h the t r a i n i n g food and a n o v e l f o o d , t r o u t s e l e c t e d a s m a l l e r p r o p o r t i o n of the t r a i n i n g f o o d i n the l a s t h a l f of the t e s t s e s s i o n . T h i s r e s u l t seemed c o n t r a r y to r e s u l t s f o r other a n i m a l s . With i n c r e a s i n g s a t i a t i o n , carp s e l e c t e d p r o g r e s s i v e l y more p r e -f e r r e d prey ( I v l e v , 1961). Animals as d i v e r s e as s t i c k l e b a c k s and cows s e l e c t e d g r e a t e r p r o p o r t i o n s of p r e f e r r e d food toward the end of a f e e d i n g s e s s i o n (Beukema, 1968; Hafez and S c h e i n , 1962). My i n t e r p r e t a t i o n of the r e s u l t s f o r t r o u t i s t h a t the t r a i n i n g food was not e q u i v a l e n t to a p r e f e r r e d f o o d . In the other s i t u a t i o n s , the a n i m a l s had c o n s i d e r a b l e exper ience w i t h a l l t e s t f o o d s , so were presumably aware of other a l t e r -n a t i v e s when c h o o s i n g one of them. The t r o u t , however, became aware of the n o v e l f o o d and s e l e c t e d a g r e a t e r p r o p o r -t i o n of i t w i t h s a t i a t i o n . Hunger l e v e l s can be d e f i n e d r e l a t i v e to the d u r a t i o n of time an animal was d e p r i v e d of food by an experimenter ( H o l l i n g , 1966; Beukema, 1968). Such hunger d i d not have a measurable i n f l u e n c e on the degree of s e l e c t i o n by t r o u t w i t h a t r a i n i n g b i a s . An e f f e c t might have been e v i d e n t w i t h a 96 l a r g e r sample s i z e or more f r e q u e n t d e p r i v a t i o n t i m e s . One might expect decreased s e l e c t i o n of t r a i n i n g f o o d w i t h i n c r e a s e d d e p r i v a t i o n , i f t r a i n i n g bias were the same as f o o d p r e f e r e n c e . T r o u t w i t h a t r a i n i n g b i a s s t r u c k and r e j e c t e d the n o v e l food d i s p r o p o r t i o n a t e l y . C o n t r o l s t r a i n e d on both foods or a t h i r d food d i d not r e j e c t the t e s t foods d i f f e r e n t i a l l y . The t r o u t presumably used c h e m i c a l cues and g u s t a t i o n to d i s c r i m i n -ate between the t e s t foods, as o l f a c t i o n and g u s t a t i o n are v e r y acute senses i n salmonids ( S u t t e r l i n and S u t t e r l i n , , 1970J 1971). The b e h a v i o r a l mechanism of t r a i n i n g b i a s was c o n d i t i o n i n g to some set of s t i m u l i from the f o o d . Rainbow t r o u t become c o n d i t i o n e d to v i s u a l s t i m u l i (Rensch, 1959; Ware, MS 1971). Salmon, and presumably t r o u t , become c o n d i t i o n e d to chemical p r o p e r t i e s of food (McBride , et. .a l . , 1962). In p r e l i m i n a r y o b s e r v a t i o n s , t r o u t responded and o r i e n t e d to d i s s o l v e d food e x t r a c t s , but they seemed unable to f o l l o w a c o n c e n t r a t i o n g r a d i e n t ( J . E . Bardach , p e r s o n a l communicat ion) . S i n c e anosmic t r o u t can f e e d ( S u t t e r l i n and S u t t e r l i n , 1970), o l f a c -t o r y cues are not n e c e s s a r y . I t i s w e l l known by f i s h e r m e n t h a t v i s u a l cues are s u f f i c i e n t to e l i c i t f e e d i n g b e h a v i o r i n t r o u t . As v i s u a l s t i m u l i are the o n l y k i n d a v a i l a b l e at the d i s t a n c e from which a d u l t t r o u t a t t a c k , i t i s g e n e r a l l y thought t h a t v i s u a l cues e l i c i t and d i r e c t t h e i r a t t a c k (Ware, MS 1971; S u t t e r l i n and S u t t e r l i n , 1970). However, i t seems 97 l i k e l y t h a t o l f a c t o r y cues c o u l d s e n s i t i z e t r o u t to v i s u a l ones i n some i n s t a n c e s . D u r i n g my t e s t s f o r t r a i n i n g b i a s , t r o u t u s u a l l y a t t a c k e d from d i s t a n c e s l e s s than 3 cm, and data of S u t t e r l i n and S u t t e r l i n (1971) suggest t h a t o l f a c t o r y s t i m -u l i might have been p a r t l y r e s p o n s i b l e f o r e l i c i t i n g s t r i k e s . W i t h i n t r e a t m e n t s , i n d i v i d u a l d i f f e r e n c e s i n food s e l -e c t i o n were apparent o n l y i n the t reatment w i t h t r o u t t r a i n e d on both t e s t f o o d s . In t h i s t reatment the average t r o u t ate a p r o p o r t i o n of the two foods which was more s i m i l a r to the p r o p o r t i o n i t had eaten p r e v i o u s l y than to the p r o p o r t i o n s eaten by other i n d i v i d u a l s . S e l e c t i o n by these t r o u t c o u l d more p r o p e r l y be c a l l e d a p r e f e r e n c e s i n c e they had c o n s i d e r -able p r e v i o u s exper ience w i t h b o t h f o o d s . Brown (1969) o b -served the same phenomenon i n pigeons which had been f e d a mixture of p l a n t seeds f o r a l o n g p e r i o d of t i m e . The amount of t r a i n i n g neces s a r y f o r d e t e c t a b l e t r a i n i n g b i a s was about 9 meals . In two exper iments , t r a i n i n g b i a s e s were e v i d e n t a f t e r 9 meals ; b i a s e s were not e v i d e n t a f t e r 6 or 7 meals . I t i s p o s s i b l e t h a t l a r g e r sample s i z e s c o u l d have d e t e c t e d b i a s e s sooner . A p p r o x i m a t e l y 10 days (one meal each day) were r e q u i r e d to c o n d i t i o n young salmon to chemical e x t r a c t s of f o o d (McBride et a l . , 1962). Ware (MS 1971) found t h a t about 7 days or 42 t r i a l s (6 t r i a l s per day with food r e i n f o r c e m e n t a f t e r each t r i a l ) were n e c e s s a r y to t r a i n rainbow 98 t r o u t to respond maximally to v i s u a l s t i m u l i . T r a i n i n g on a s i n g l e food beyond the minimum n e c e s s a r y f o r the e x p r e s s i o n of a t r a i n i n g b i a s d i d not s i g n i f i c a n t l y i n c r e a s e the degree of s e l e c t i o n f o r the t r a i n i n g f o o d . W i t h t u b i f e x or b r i n e shr imp, t r o u t ate about 70% f a m i l i a r food a f t e r 9 to 75 t r a i n i n g meals . A f t e r c o n d i t i o n i n g to one of two t a r g e t s d i f f e r i n g i n p a t t e r n or c o l o r , rainbow t r o u t r e a c t e d to the c o n d i t i o n e d t a r g e t i n 80 and 85% of the t r i a l s (Rensch, 1959). I t i s p o s s i b l e t h a t a s t i l l longer t r a i n i n g p e r i o d c o u l d a l s o i n c r e a s e the degree of s e l e c t i o n f o r the t r a i n i n g f o o d . However, 75 meals of a s i n g l e food i s c o n s i d e r a b l e t r a i n i n g f o r an animal l i k e a t r o u t . In n o r t h temperate r e g i o n s , i n d i v i d u a l t r o u t u s u a l l y eat a number of d i f f e r e n t k i n d s of prey each day and d i f f e r e n t k i n d s a t d i f f e r e n t seasons of the y e a r . Thus t r a i n i n g e q u i v a l e n t to 75 meals i s u n l i k e l y . I t i s a l s o p o s s i b l e t h a t w i t h d i f f e r e n t f o o d s , the e f f e c t of t r a i n i n g d u r a t i o n on degree of s e l e c t i o n would be g r e a t e r . However, the degree of s e l e c t i o n a c h i e v e d w i t h the o ther t r a i n i n g foods I used was about the same as w i t h t u b i f e x and b r i n e s h r i m p . My i n t e r p r e t a t i o n of the r e s u l t s i s t h a t w i t h two e q u a l l y a c c e p t a b l e f o o d s , i n c r e a s e d t r a i n i n g does not g r e a t l y i n c r e a s e the degree of s e l e c t i o n f o r the f a m i l i a r one i n rainbow t r o u t . T h i s seems s i m i l a r to t h e e f f e c t of t r a i n i n g i n an i n s e c t . H e l i o t h i s l a r v a e s e l e c t e d the f a m i l i a r f o o d to about the same degree whether they had been t r a i n e d u n t i l the s i x t h and l a s t i n s t a r or t r a i n e d f o r o n l y 48 hr 99 d u r i n g the s i x t h i n s t a r ( T i b o r , Hanson, and D e t h i e r , 1968). Carp are r e p o r t e d to show i n c r e a s i n g e l e c t i v i t y f o r ( s e l e c t i o n o f ) f a m i l i a r f o o d w i t h i n c r e a s i n g t r a i n i n g ( i v l e v , 1955; 1961). However, t h i s c o n c l u s i o n i s based upon data which cannot be o b t a i n e d u s i n g the procedure i n d i -cated i n e i t h e r the o r i g i n a l R u s s i a n p u b l i c a t i o n ( i v l e v , 1955) or the E n g l i s h t r a n s l a t i o n ( I v l e v , 1961). The e l e c t -i v i t y v a l u e s f o r 20 and 30 days of t r a i n i n g ( i v l e v , 1955; 1961: T a b l e 23) are l a r g e r than p o s s i b l e i f the food d e n s i t i e s were equal as i m p l i e d . The e l e c t i v i t y v a l u e s f o r 0 and 2 days of t r a i n i n g are c o n s i s t e n t w i t h those of other e x p e r i -ments i n which the d e n s i t i e s were e q u a l . Presumably, the f o o d d e n s i t i e s were not equal i n a l l t e s t s , or a t r a n s f o r m -a t i o n was a p p l i e d to some of the e l e c t i v i t y v a l u e s ( ¥ . E . R i c k e r , personal communicat ion) . D e s p i t e the d i s c r e p a n c i e s , i t seems l i k e l y t h a t carp d i d show i n c r e a s e d s e l e c t i o n of f a m i l i a r f o o d w i t h i n c r e a s e d t r a i n i n g as r e p o r t e d by the l a t e P r o f e s s o r I v l e v . Thus carp may be u n l i k e t r o u t i n t h i s r e s p e c t . I t i s not com-p l e t e l y c l e a r t h a t the e x p e r i m e n t a l s i t u a t i o n s were compar-a b l e , however, as s p e c i f i c d e t a i l s about e x p e r i m e n t a l p r o -cedure were not p r o v i d e d f o r c a r p . Carp p r o b a b l y had to s e a r c h substratum to o b t a i n l i v i n g prey whereas t r o u t d i d n o t . The r e s u l t s f o r carp ( I v l e v , 1955; 1961: T a b l e s 22 and 23 (0 and 2 meals) ) were s i m i l a r to r e s u l t s of an e x p e r -iment (Table 10) w i t h substratum and p r o b a b l y l i v e p r e y . ¥ h e n t r a i n e d on two foods i n s u c c e s s i o n , t r o u t s e l e c t e d 100 the second f o o d . The c o n t r o l s showed t h a t such s e l e c t i o n r e s u l t e d from c o n d i t i o n i n g to the second food and not j u s t from f o r g e t t i n g the f i r s t . A l t h o u g h t r a i n e d on each food f o r 12 meals , the t r o u t presumably ate more o f the second food because they had grown d u r i n g the t r a i n i n g p e r i o d . When snapping t u r t l e s were t r a i n e d i n the same manner, however, they " p r e f e r r e d " the f i r s t f o o d (Burghardt and Hess , 1966; B u r g h a r d t , 1967). The c r i t e r i o n f o r p r e f e r e n c e i n t u r t l e s was the t e s t food chosen f i r s t . However t r o u t d i f f e r e d - f r o m t u r t l e s a c c o r d i n g to t h i s c r i t e r i o n a l s o . A p p a r e n t l y , the f i r s t f o o d encountered a f t e r h a t c h i n g produces a more . l a s t i n g e f f e c t i n snapping t u r t l e s than i n rainbow t r o u t . In the r e d - e a r e d t u r t l e , the e f f e c t of the f i r s t food d i d not seem as s t r o n g as i n the snapping t u r t l e (Mahmoud and Lavenda, 1969), a l t h o u g h d i r e c t comparison was not p o s s i b l e . In H e l i o t h i s l a r v a e , a b i a s f o r f a m i l i a r food was r e p l a c e d by b i a s f o r n o v e l f o o d w i t h one p a i r o f foods but not w i t h another ( T i b o r , Hanson, and D e t h i e r , 1968). When t r o u t were o f f e r e d b o t h the f a m i l i a r and a n o v e l food a f t e r t r a i n i n g , they c o n t i n u e d to s e l e c t the t r a i n i n g food i n s e v e r a l t e s t meals . Two experiments i n d i c a t e d t h a t b i a s e s p e r s i s t e d f o r 14 to 23 meals of b o t h f o o d s . A l t h o u g h there was a s i g n i f i c a n t t r a i n i n g bias a f t e r meal 18, the r e s u l t was l a r g e l y determined by one i n d i v i d u a l ; t h i s i m p l i e s t h a t f o r t h e m a j o r i t y of f i s h , the b i a s was weaker than apparent i n the data p r e s e n t e d . The d u r a t i o n of v o l -u n t a r y maintenance d i d not seem to be r e l a t e d to the amount 101 of o r i g i n a l t r a i n i n g s i n c e the b i a s e s p e r s i s t e d f o r about the same i n t e r v a l whether t r o u t had been t r a i n e d f o r 12 or 75 meals . The p e r s i s t e n c e of t r a i n i n g b i a s e s i n t r o u t was s i m i l a r to t h a t r e p o r t e d f o r some i n v e r t e b r a t e p r e d a t o r s . ¥ h e n s t a r -f i s h were f e d the t r a i n i n g food and a food which they had s e l e c t e d b e f o r e t r a i n i n g , the b i a s d i d not p e r s i s t f o r as l o n g as the o r i g i n a l t r a i n i n g p e r i o d (Landenberger , 1968). The b i a s p e r s i s t e d f o r a l o n g e r but undetermined p e r i o d when s t a r f i s h had eaten the two foods i n n e a r l y the same p r o p o r t i o n p r i o r t o t r a i n i n g . Marine s n a i l s t r a i n e d on prey which were about e q u a l l y a c c e p t a b l e , r e t a i n e d t r a i n i n g b i a s e s f o r a l o n g e r t ime than the o r i g i n a l t r a i n i n g p e r i o d (Murdoch, 1969). The r e s u l t s of a l l experiments together suggest t h a t t r a i n i n g b i a s e s i n t r o u t are r e l a t i v e l y weak, and t h e r e f o r e p r o b a b l y make l i t t l e d i f f e r e n c e to f o o d s e l e c t i o n i n n a t u r a l s i t u a t i o n s . A p p r o x i m a t e l y 9 t r a i n i n g meals were necessary to induce a t r a i n i n g b i a s . Even t h e n , f a m i l i a r food was only eaten 70$ of the t i m e . Moreover , the r e s u l t s w i t h l i v e prey showed that o ther aspec ts of the p r e d a t o r - p r e y s i t u a t i o n can be more impor tant than t r a i n i n g i n d e t e r m i n i n g food s e l e c t i o n i n more n a t u r a l s i t u a t i o n s . In a pine wood, the responses of t i t m i c e to prey changed i n a way which was d i s p r o p o r t i o n a t e to changes i n the abundance of the prey s p e c i e s ( T i n b e r g e n , 1960). U s u a l l y , prey d e n s i t i e s were measured o n l y once, but they seemed constant d u r i n g the p e r i o d s when food c o l l e c t e d by t i t s was 102 b e i n g o b s e r v e d . Sudden changes f r e q u e n t l y o c c u r r e d i n the p r o p o r t i o n s of d i f f e r e n t prey c a p t u r e d by i n d i v i d u a l b i r d s . These changes o c c u r r e d a t d i f f e r e n t t imes f o r d i f f e r e n t i n d i v -i d u a l s s e a r c h i n g i n areas w i t h s i m i l a r prey c o m p o s i t i o n s . Such o b s e r v a t i o n s were i n t e r p r e t e d to mean t h a t the t i t s became c o n d i t i o n e d to v i s u a l p r o p e r t i e s of p a r t i c u l a r food organisms and c a p t u r e d these d i f f e r e n t i a l l y . Crows l e a r n e d to r e c o g n i z e p a r t i c u l a r v i s u a l c h a r a c t e r -i s t i c s of o b j e c t s c o v e r i n g f o o d ( C r o z e , 1970). A f t e r f i n d i n g or b e i n g taught to f i n d f o o d under m o l l u s c s h e l l s , the crows would l o o k f o r food under other s h e l l s which were s i m i l a r i n shape and c o l o r . In d o i n g so , the crows more f r e q u e n t l y t u r n e d over s h e l l s r e s e m b l i n g those c o v e r i n g the food they had p r e v i o u s l y found than s h e l l s which d i f f e r e d i n c o l o r or shape. Thus , they were s e l e c t i v e i n the s t i m u l i they responded to '— and perhaps i n the s t i m u l i they p e r c e i v B d — w h i l e s e a r c h i n g f o r f o o d . In b o t h crows and t i t s , the mechanisms u n d e r l y i n g the observed f o o d s e l e c t i o n were thought to i n v o l v e s e l e c t i v e p e r c e p t i o n of p o t e n t i a l f o o d o b j e c t s , hence both the mechan-ism and the f o o d s e l e c t i o n have been d e s c r i b e d w i t h the term s e a r c h i n g image ( C r o z e , 1970). However, there i s no d i r e c t evidence about the extent to which such f o o d s e l e c t i o n r e s u l t e d from a p e r c e p t u a l f i l t e r and the extent to which i t r e s u l t e d from d i f f e r e n t i a l response to s t i m u l i a s s o c i a t e d w i t h food eaten p r e v i o u s l y . Moreover , d i f f e r e n c e s i n food 103 s e l e c t i o n of great t i t s can be e x p l a i n e d by assuming t h a t they p e r c e i v e many p o t e n t i a l foods but s e a r c h i n d i f f e r e n t h a b i t a t s (Royama, 1970). The d i s t r i b u t i o n of food organisms eaten by great t i t s was heterogeneous among d i f f e r e n t s u b -h a b i t a t s . Food d i s t r i b u t i o n s l i k e those captured by t i t s c o u l d be generated by t i t s s e a r c h i n g i n d i f f e r e n t s u b h a b i t a t s , and thereby o p t i m i z i n g t h e i r h u n t i n g e f f i c i e n c y (Royama, 1970). Even though food s e l e c t i o n r e s u l t e d from c o n d i t i o n i n g i n both crows ( C r o z e , 1970) and t r o u t , the nature of f o o d s e l e c t i o n i n t r o u t d i f f e r e d from t h a t i n crows. Crows s e l e c t e d a new f o o d a f t e r a few t r i a l s (average = 2 . 3 ; C r o z e , 1970), whereas the t r o u t r e q u i r e d many t r i a l s (9 meals) to d e v e l o p a t r a i n i n g b i a s . F u r t h e r m o r e , when crows d i s c o v e r e d t h a t a new k i n d of s h e l l covered f o o d , t h e i r response r a t e to t h a t k i n d of s h e l l i n c r e a s e d immediate ly ( C r o z e , 1970). The f o r m e r l y n o v e l s h e l l was then a t l e a s t as l i k e l y to be t u r n e d as the f o r m e r l y f a m i l i a r one which no l o n g e r covered f o o d . However, most t r o u t (52 - 57$) ate the n o v e l food d u r i n g t h e i r f i r s t t e s t but c o n t i n u e d to s e l e c t the f a m i l i a r food a f t e r many encounters w i t h the n o v e l one. U n l i k e crows, t r o u t c o n t i n u e d to choose the f a m i l i a r food a f t e r becoming aware of the new one. In a d d i t i o n to the s imultaneous c h o i c e s i t u a t i o n , the f o o d d i s t r i b u t i o n s were s i m p l i f i e d , and many components of s e a r c h i n g b e h a v i o r i g n o r e d i n the experiments . I n n a t u r a l s i t u a t i o n s , p o t e n t i a l prey s p e c i e s are d i s t r i b u t e d h e t e r o -geneously i n space ( G e r k i n g , 19 62; H a r g r a v e , 1970) and time 104 (Mundie, 1959; ¥ a r e MS 1971). C o n s e q u e n t l y , d i f f e r e n t t r o u t which respond t o , s e a r c h f o r , and capture p r e y i n e x a c t l y the same manner might eat d i f f e r e n t prey because they happened to hunt i n d i f f e r e n t areas or at d i f f e r e n t times of day. But s e a r c h i n g and c a p t u r i n g t e c h n i q u e s p r o b a b l y d i f f e r among i n d i v i d u a l s . Because some t e c h n i q u e s are more e f f i c i e n t than others i n o b t a i n i n g p a r t i c u l a r prey types ( S c h u t z , MS 1969), t r o u t w i l l become p r o f i c i e n t i n p r o c u r i n g t h e i r most commonly eaten p r e y . In n a t u r a l s i t u a t i o n s , t h e r e f o r e , i n d i v -i d u a l t r o u t may s e l e c t d i f f e r e n t prey f o r many reasons b e s i d e s any d i f f e r e n c e i n t r a i n i n g b i a s . 105 RESULTS PART I I E f f e c t s of P a r e n t a l Stock on Pood S e l e c t i o n S e l e c t i o n of d a p h n i a , mayf ly l a r v a e , and h a t c h e r y food Three experiments were performed to f i n d out whether rainbow t r o u t would s e l e c t food commonly eaten by t h e i r parents when they were n a i v e (without p r e v i o u s f e e d i n g e x p e r i e n c e ) . Experiment 11 used young of domestic and two w i l d s t r a i n s . The w i l d s t r a i n s were chosen because the l a k e s they i n h a b i t e d , Loon Lake and S w a l w e l l Lake (50 119 SE) d i f f e r e d i n morphology and hence i n p r o p o r t i o n s of food types p r e s e n t . As d e s c r i b e d by N o r t h c o t e (1962), Loon Lake i s deep and l a c k i n g i n l i t t o r a l a r e a . S w a l w e l l i s s h a l l o w e r and t h e r e f o r e produces more b e n t h i c f a u n a . Hartman (MS 1954) found t h a t both young and a d u l t t r o u t i n Loon Lake ate m a i n l y c l a d o c e r a (more t h a n 50$ c l a d o c e r a and l e s s than 20$ i n s e c t s by weight ) f r o m May through September. A sample taken i n mid-June from S w a l w e l l Lake , i n d i c a t e d t h a t the 56 a d u l t s had eaten e x c l u s i v e l y bottom organisms (unpub-l i s h e d d a t a , B. C. F i s h and V i l d l i f e B r a n c h ) . Eggs of domestic and Loon parents were c o l l e c t e d s i m u l -t a n e o u s l y (May 2, 1968). Eggs of S w a l w e l l parents were not a v a i l a b l e u n t i l 33 days l a t e r , and o b s e r v a t i o n of food s e l e c t i o n by young Swalwel l s t o c k was d e l a y e d a c c o r d i n g l y . A l l t e s t meals used one k i n d of p l a n k t o n i c organism , b e n t h i c organism, and h a t c h e r y f o o d . I f young t r o u t s e l e c t t h e food of t h e i r p a r e n t s , domestic s tock would s e l e c t h a t c h e r y f o o d , Loon s t o c k 106 p l a n k t o n , and S w a l w e l l s t o c k m a y f l y l a r v a e . Each n a i v e t r o u t was o f f e r e d 12 daphnia and 8 mayf ly l a r v a e ; the d e n s i t i e s o f f e r e d t r o u t t r a i n e d on h a t c h e r y food v a r i e d about a mode of 27 daphnia and 18 mayf ly l a r v a e (range 18:12 to 30 :20 ) . In a l l t e s t s , about 1900 p i e c e s (84 mg) h a t c h e r y food were o f f e r e d each f i s h . As the food was counted a f t e r d i s s e c t i o n , i t was not p o s s i b l e to determine how many p i e c e s of h a t c h e r y food had been e a t e n ; so a f i s h was c l a s s e d o n l y as h a v i n g eaten h a t c h e r y f o o d or n o t . Table X l V a shows t h a t a l l s t r a i n s s e l e c t e d mayf ly l a r v a e r e l a t i v e to d a p h n i a , a l t h o u g h not to the same degree . Naive Loon s t o c k s e l e c t e d an even g r e a t e r p r o p o r t i o n of m a y f l y l a r v a e than the other s t r a i n s . T h i s tendency was not so apparent a f t e r s e v e r a l meals of h a t c h e r y f o o d . There was no d i f f e r e n c e among the s tocks i n the p r o p o r t i o n which ate h a t c h e r y f o o d (Table X l V b ) . Few t r o u t ate h a t c h e r y f o o d , and of those t h a t d i d , o n l y one (naive Loon s tock) d i d not eat organisms as w e l l . Thus , n a i v e t r o u t of a l l three s tocks c l e a r l y s e l e c t e d food i n the o r d e r : mayf ly l a r v a e > daphnia => h a t c h e r y f o o d . Domestic t r o u t were s l i g h t l y l a r g e r than w i l d t r o u t (Table X I V c ) . S e l e c t i o n of h a t c h e r y f o o d and l i v e p l a n k t o n Experiment 12 ( J u l y 1970) was d e s i g n e d to t e s t the same h y p o t h e s i s , t h a t n a i v e t r o u t would s e l e c t the food of t h e i r p a r e n t s , but o n l y the domestic and Loon s tocks were u s e d . The t r o u t were t e s t e d f o r 5-min p e r i o d s w i t h foods i n t r o d u c e d at the s u r f a c e of a p l a s t i c c o n t a i n e r (500 m l ) . Each t r o u t TABLE XlVa. Number of daphnia and mayfly larvae eaten by naive t r o u t of three p a r e n t a l stocks when o f f e r e d : daphnia, mayfly l a r v a e , and hatchery food. The r e l -a t i v e d e n s i t y of daphnia to mayfly larvae was always 3 to 2, but absolute d e n s i t i e s d i f f e r e d as described i n the t e x t . No. of Meals STOCK Chi of Hatchery Domestic Loon Swalwell Square Food Value ^ -daphnia larvae . daphnia larvae daphnia la r v a e 0 50 56 6 34 45 62 12.883 2 .002 2, 4, 8, 20 84 112 42 79 - 1.747 1 .183 TABLE X l V b . Number of t r o u t d e s c r i b e d above which ate ( + ) or d i d not. eat (-) h a t c h e r y f o o d , or d i d not eat any food (0 ) . No. of Meals : STOCK C h i of Hatchery Domestic Loon S w a l w e l l Square Food + _ o + - 0 + _ 0 V a l u e df p < 0 2 1 2 1 2 1 3 0 6 1 5 1 1.667 2 .43 8 2, 4, 8, 20 11 8 0 9 10 0 - - - .106 1 .742 109 TABLE X I V c . The mean f o r k l e n g t h (mm, w i t h SE i n parentheses ) of each s t o c k , d e s c r i b e d above, a f t e r p r e s e r v a t i o n i n 10$ f o r m a l i n . No. of Meals of H a t c h e r y Food Domestic Loon S w a l w e l l STOCK 0 24.40 23.47 24.68 (0.273) (0.236) (0.179) 2, 4, 8, 20 25.84 24.37 (0.594) (0.413) 11 0 was o f f e r e d a p p r o x i m a t e l y 1600 c l a d o c e r a , 760 copepoda, and 1500 p i e c e s (84 mg) of h a t c h e r y f o o d . A l t h o u g h i n t r o d u c e d at the s u r f a c e , h a t c h e r y f o o d sank d u r i n g each t e s t . A l l f i s h r e c e i v e d p l a n k t o n c o l l e c t e d l e s s than 12 hr b e f o r e . T e s t s of domestic s tock were i n i t i a t e d 2 hr a f t e r t e s t s of w i l d s t o c k were completed . The w i l d s t o c k (same as i n Experiments 7 and 10) were r e a r e d and t e s t e d i n my l a b o r a t o r y , but the domestic s t o c k were r e a r e d and t e s t e d elsewhere ( U n i v e r s i t y of B r i t i s h C o l u m b i a , South Campus). The domestic f i s h had not been a c c l i m a t e d to l i g h t i n t e n s i t y adequate f o r t e s t i n g , and o n l y 60$ ate a n y t h i n g d u r i n g a t e s t . C o n s e q u e n t l y , o n l y those f i s h which f e d were used i n a n a l y s i s . T a b l e XV i n d i c a t e s t h a t n a i v e domestic t r o u t d i d not eat more h a t c h e r y f o o d r e l a t i v e to p l a n k t o n than w i l d s t o c k . In f a c t , the r e v e r s e o c c u r r e d . There was no s i g n i f i c a n t d i f f e r -ence between s t o c k s i n p r o p o r t i o n of h a t c h e r y f o o d eaten and r e j e c t e d . Consumption of l i v i n g and n o n - l i v i n g p l a n k t o n Experiment 13 was designed to t e s t f o r d i f f e r e n c e s between s t r a i n s i n s t i l l another way. S ince domestic t r o u t eat m a i n l y n o n - l i v i n g food and w i l d t r o u t m a i n l y l i v i n g f o o d , one might expect the same response i n n a i v e o f f s p r i n g . A c c o r -d i n g l y , n a i v e young of both s t o c k s were o f f e r e d l i v e and dead p l a n k t o n . Experiment 13 was done i n J u l y 1969 w i t h t h e same l o t s of f i s h as Experiments 2, 3, and 4. H a l f the t r o u t were t e s t e d s i n g l y and h a l f i n groups of 5. Each TABLE XV. Food of n a i v e domestic and w i l d s tocks (20 of each) o f f e r e d l i v e p l a n k t o n and h a t c h e r y f o o d . Domestic Stock W i l d S t o c k C h i df p < Hatchery P l a n k t o n Hatchery P l a n k t o n Square Food Food Value Food E a t e n Food Examined 14 49 328 341 16 77 1 58 287 4 .59 9.37 .031 .003 Mean Length (mm) SE 26.85 0.257 25.85 0.199 112 aquarium c o n t a i n e d 10 l i t e r s and a p p r o x i m a t e l y 5000 organisms (65% c l a d o c e r a , 28% copepoda, and 7% o t h e r ) . A l l f i s h were f e d s i m u l t a n e o u s l y ( f o r 3 h r ) and r e c e i v e d e i t h e r l i v e or f r e s h l y k i l l e d , p l a n k t o n c o l l e c t e d l e s s than 4 hr b e f o r e . A f t e r p r e s e r v a t i o n , domestic t r o u t (x = 25.04 mm, SE = 0.196) were l o n g e r than w i l d ones (x = 24.67 mm, SE = 0 .106) . The r e s u l t s of Experiment 13 are p r e s e n t e d i n T a b l e s XVIa and X V I b . Domestic s tock ate more than w i l d whether food was l i v e or dead. Trout o f both s t r a i n s consumed more l i v e than dead f o o d ; they consumed more food when i n a group than when s i n g l e . There were no s i g n i f i c a n t i n t e r a c t i o n s . T h e r e f o r e , the d i f f e r e n c e i n r e l a t i v e consumption of l i v e and dead p l a n k t o n was the same f o r both s t o c k s . The data of T a b l e XVIa were t ransformed to l o g a r i t h m s to ensure n o r m a l i t y and a d d i t i v i t y . When the a n a l y s i s was repeated f o r c l a d o c e r a a l o n e , the e f f e c t s of s t o c k and f o o d were a g a i n apparent , but the e f f e c t of s o c i a l s i t u a t i o n was n o t . To determine the i m p o r t a n c e . o f movement i n e l i c i t a t i o n of an a t t a c k , I p r e s e n t e d t r o u t s i m u l t a n e o u s l y w i t h moving and s t a t i o n a r y prey models ( g l a s s beads 5 cm a p a r t ) . T r o u t a t t a c k e d the moving model much more f r e q u e n t l y than the s t a t i o n a r y one. The r e s u l t s of Experiment 13 were examined to s e e whether i n d i v i d u a l t r o u t sampled the two food types a t random. W^en food was dead, copepoda and c l a d o c e r a were not d i s t r i b u t e d randomly among the f i s h of e i t h e r s t o c k or s o c i a l s i t u a t i o n ( a v e r a g e ^ = 77 .4 , 9 d f , p «=: 0 .001) . Some f i s h a t e m a i n l y 113 TABLE X V I a . E f f e c t of s t o c k , nature o f f o o d , and s o c i a l s i t u a t i o n on l o g number of p l a n k t o n i c organisms eaten by n a i v e t r o u t . The domestic and w i l d s tock (40 of each) were a l l o c a t e d to two t r e a t m e n t s : f e e d i n g on l i v e or dead p l a n k t o n ; f e e d i n g s i n g l y or i n a group of f i v e . Source of V a r i a t i o n df Mean Square E p <; Stock of t r o u t (ST) 1 2.2241 10.12 .005 Nature of food (NF) 1 2.8598 13.02 .001 S o c i a l s i t u a t i o n (SSIT) 1 1.3290 6.05 .025 ST x NF 1 0.0299 0.13 .75 NF x SSIT 1 0.2727 1 .24 .50 ST x SSIT 1 0.0234 0.11 .75 ST x NF x SSIT 1 0.0736 0.34 .75 Remainder 72 0.2197 TABLE XVIb . Mean a r i t h m e t i c number of organisms eaten per i n d i v i d u a l . The average s t a n d a r d e r r o r was . 3 .840, n = 10. Stock of t r o u t S o c i a l S i t u a t i o n Nature o f Food A l i v e Dead Domestic V i l d Group S i n g l e Group S i n g l e 43.50 39.30 31 .00 28.10 32.30 25.80 24.50 14.90 114 c l a d o c e r a and o t h e r s m a i n l y copopoda. When food was a l i v e , however, a l l f i s h ate m a i n l y c l a d o c e r a , which were e a s i e r to c a t c h . T es ts of h e t e r o g e n e i t y i n the l i v e food treatment were not made because the expected v a l u e s f o r copepoda were too low. Other d i f f e r e n c e s between domest ic and w i l d s t o c k s P r e l i m i n a r y experiments on other b e h a v i o r a l f e a t u r e s of the two s t r a i n s were performed to f i n d out whether i n d i v i d u a l s d i f f e r e d i n f e e d i n g p r o p e n s i t y . To t e s t the h y p o t h e s i s t h a t domestic s t o c k would remain nearer the s u r f a c e (where hatchery food i s n o r m a l l y p r e s e n t e d ) , the d i s t r i b u t i o n s of 40 t r o u t of each s t o c k w i t h i n l a r g e a q u a r i a were observed r e p e a t e d l y . S l i g h t l y more w i l d s t o c k were near the s u r f a c e when the f i s h were n a i v e , but a f t e r 12 to 70 meals of ha tchery f o o d , s l i g h t l y more domestic s tock were near the s u r f a c e ( d i f f e r -ences s i g n i f i c a n t , p < 0 . 0 0 l ) . Naive t r o u t of each s t o c k were e q u a l l y s u c c e s s f u l i n c a p t u r i n g the p l a n k t o n whichthey a t t a c k e d , but the sample s i z e was s m a l l (n = 9 / s t o c k ) . Ob-* s e r v a t i o n s on capture success were not c o n t i n u e d because the domestic f i s h had a s i z e advantage and seemed to have a swimming advantage f o r which no c o n t r o l was a p p a r e n t . When n a i v e , the two s t r a i n s were e q u a l l y capable of d i s c r i m i n a t i n g between f o o d and n o n - f o o d ( p l a n k t o n and d e b r i s , n = 9, or h a t c h e r y f o o d and sawdust, n = 18) . In 5-min t e s t s , dom-e s t i c s t o c k r e j e c t e d l e s s h a t c h e r y food than w i l d s t o c k , but the o b s e r v a t i o n s l a c k e d s u f f i c i e n t c o n t r o l to r u l e out any e f f e c t of d i f f e r e n t i a l s a t i a t i o n r a t e . 11 5 DISCUSSION OF PART II None of the experiments i n d i c a t e d t h a t young t r o u t s e l -ec t ed the type of food commonly eaten by t h e i r p a r e n t s . I t i s p o s s i b l e to i n t e r p r e t such r e s u l t s i n s e v e r a l d i f f e r e n t ways. The i n t e r p r e t a t i o n s which seem most c o n s i s t e n t w i t h other i n f o r m a t i o n are o u t l i n e d i n the f o l l o w i n g p a r a g r a p h s . The experiments were i n t e n d e d to determine whether d i f f -erences , i n f o o d of p a r e n t a l s t o c k can i n f l u e n c e food s e l e c t i o n by progeny. They were n o t i n t e n d e d to d i s t i n g u i s h between g e n e t i c and maternal e f f e c t s . Because the experiments were d e s i g n e d to determine whether p a r e n t a l s t o c k can i n f l u e n c e f o o d s e l e c t i o n of progeny, a l l made two important assumptions : 1) t h a t the envi ronmenta l d i f f e r e n c e s were s u f f i c i e n t to produce d i f f e r e n c e s i n the p a r e n t a l s t o c k s , 2) t h a t the e x p e r i m e n t a l s i t u a t i o n s were adequate to f i n d a d i f f e r e n c e i n the tendency of the o f f s p r i n g to eat d i f f e r e n t f o o d s . The f i r s t assumption was p r o b a b l y warranted i n the case of w i l d and domest ic s t o c k s . Perhaps the most important d i f f e r e n c e between them was t h a t domestic s t o c k grew much b e t t e r on hatchery f o o d , as r e p o r t e d p r e v i o u s l y ( V i n c e n t , 1960; Mason, B r y n i l d s o n , and Degurse , 1967). S i n c e h a t c h e r y c o n d i t i o n s produced a s t o c k which grows f a s t on h a t c h e r y f o o d , there had presumably been s e l e c t i o n f o r i n d i v i d u a l s which accept h a t c h e r y f o o d r e a d i l y . T h i s does not n e c e s s a r i l y mean that t h e r e had been s e l e c t i o n a g a i n s t i n d i v i d u a l s which r e a d i l y accepted a l l k i n d s of f o o d , however. I n f a c t , domestic 116 s t o c k ate more food than w i l d s t o c k i n a l l exper iments . In my l a b o r a t o r y , domestic s t o c k grew as w e l l as or b e t t e r than w i l d on h a t c h e r y food and s e v e r a l d i f f e r e n t l i v e and dead organisms. There was l e s s evidence t h a t the Loon and S w a l w e l l s t o c k s were s u f f i c i e n t l y d i f f e r e n t . As d e s c r i b e d p r e v i o u s l y , the d i f f e r e n c e i n l a k e morphology f a c i l i t a t e d p r o d u c t i o n of b e n t h i c r e l a t i v e to p l a n k t o n i c organisms i n S w a l w e l l Lake and the r e v e r s e i n Loon L a k e . C o n s e q u e n t l y , d e s p i t e the s c a n t y food d a t a , i t i s l i k e l y t h a t the y e a r l y d i e t of Loon s t o c k i n c l u d e d more p l a n k t o n and that of S w a l w e l l s tock more b e n t h i c organisms . S i n c e i t i s probable t h a t blooms of p l a n k t o n occur i n S w a l w e l l Lake, there may have been no s e l e c t i o n f o r f e e d i n g on bottom organisms nor a g a i n s t f e e d i n g on p l a n k t o n i n S w a l w e l l s t o c k . The normal f o o d of f r y was not n e c e s s a r i l y the same as t h a t of the a d u l t s and no i n f o r -mation was a v a i l a b l e f o r S w a l w e l l f r y . In streams, the most common foods of Loon f r y were: c h i r o n o m i d s , m a y f l i e s , and s i m u l i d s (P. A . S l a n e y , p e r s o n a l communicat ion) . Most Loon f r y , however, entered the l a k e s h o r t l y a f t e r h a t c h i n g ( N o r t h c o t e , 1962) where t h e y ate m a i n l y c l a d o c e r a and amphi-pods (Hartman, MS 1954). The second a s s u m p t i o n — t h a t the e x p e r i m e n t a l s i t u a t i o n s were a p p r o p r i a t e f o r f i n d i n g any d i f f e r e n c e — i s a l s o s u b j e c t to q u e s t i o n . The reason f o r u s i n g t e s t s w i t h h i g h food d e n s i t y was to s i m p l i f y the c h o i c e s i t u a t i o n , f a c i l i t a t i n g any tendency to s e l e c t one f o o d r e l a t i v e to the o t h e r ( s ) . Other workers found t h a t a p r e d a t o r ' s tendency to s e l e c t food was emphasized when p r e s e n t e d with h i g h d e n s i t i e s and few k i n d s of f o o d ( I v l e v , 1961; Landenberger , 1968). In Experiment 11, the foods used to t e s t the two w i l d s tocks may not have been a p p r o p r i a t e . The daphnia were not c o l l e c t e d from Loon L a k e , but were p r o b a b l y v e r y s i m i l a r to -the c l a d o c e r a t h e r e . However, the m a y f l y l a r v a e , c o l l e c t e d from a stream and chosen as a r e p r e s e n t a t i v e b e n t h i c organisms, may not have been s u f f i c i e n t l y s i m i l a r to other b e n t h i c organisms f o r S w a l w e l l s t o c k to select them. Thus i n Experiment 11, the foods may not have been a p p r o p r i a t e f o r d e t e r m i n i n g whether the two w i l d s t o c k s tended to s e l e c t d i f f e r e n t f o o d s . In a l l t h r e e experiments (11, 12, and 13), however, the t e s t s i t u a t i o n s seemed a p p r o p r i a t e f o r f i n d i n g d i f f e r e n c e s between w i l d and domest ic s t o c k s . Naive t r o u t d i d not respond d i f f e r e n t i a l l y to food of p a r e n t a l s t o c k s . My i n t e r p r e t a t i o n of t h i s i s that they d i d not r e c o g n i z e s p e c i f i c c h e m i c a l or v i s u a l p r o p e r t i e s of f o o d commonly eaten by t h e i r p a r e n t s . Others have found t h a t n a i v e salmon d i d not r e c o g n i z e chemicals i n p a r e n t a l foods (McBride e_t a J . , 1962). In young sockeye salmon, s e a r c h i n g b e h a v i o r was e l i c i t e d by chemical e x t r a c t s of f o o d , but o n l y of those foods which had been eaten p r e v i o u s l y . T h i s was t r u e of p l a n k t o n , which i s the major f o o d of young and a d u l t sockeye salmon (McCart , 1967; McBride et al_. , 1962). I t seems r e a s o n a b l e t h a t n a i v e snakes respond to chem-i c a l e x t r a c t s of p a r e n t a l foods ( D i x , 1968; B u r g h a r d t , 1970), 11 8 •whereas salmonids do not seem t o . Chemical s t i m u l i are n e c e s s a r y to e l i c i t f e e d i n g i n snakes (Burghardt , 1966; 1970), and may be used i n prey l o c a t i o n . S i n c e young snakes are presumably c o n f r o n t e d w i t h a v a r i e t y of o d o r s , they might b e n e f i t from programmed r e c o g n i t i o n of those i n d i c a t i n g good f o o d s o u r c e s . As d e s c r i b e d p r e v i o u s l y , salmonids do not f e e d i n response to c h e m i c a l cues a l o n e , and a p p a r e n t l y cannot use c h e m i c a l cues to l o c a t e p r e y . C o n s e q u e n t l y , i t would be unnecessary f o r salmonids to r e c o g n i z e c h e m i c a l c h a r a c t e r -i s t i c s of s p e c i f i c p r e y . The s tocks of t r o u t d i d not respond d i f f e r e n t l y to v i s u a l c h a r a c t e r i s t i c s of d i f f e r e n t p r e y . T h i s does not mean t h a t there were no d i f f e r e n c e s among the s tocks i n the v i s u a l s t i m u l i most e f f e c t i v e i n e l i c i t i n g f e e d i n g . There may have been d i f f e r e n t i a l response to such prey c h a r a c t e r i s t i c s a s : c o l o r , c o n t r a s t , s i z e , shape, a n d type of movement. My o n l y c o n c l u s i o n i s t h a t any such d i f f e r e n c e s were not expressed i n the t e s t s i t u a t i o n s . A l t h o u g h there was no evidence of d i r e c t s e l e c t i o n of the type of food eaten by p a r e n t a l s t o c k , w i l d s t o c k d i d r e j e c t a s l i g h t l y g r e a t e r p r o p o r t i o n of h a t c h e r y food than domestic s t o c k i n a p r e l i m i n a r y exper iment . In other e x p e r -iments (11, 12, and 13), however, domestic s t o c k ate more w i t h i n a f e e d i n g s e s s i o n than d i d w i l d s t o c k ; hence the s a t i a t i o n r a t e was d i f f e r e n t f o r the two s t o c k s . S i n c e the f r e q u e n c y of food r e j e c t i o n i n c r e a s e d w i t h s a t i a t i o n , the d i f f e r e n c e between t h e s tocks can be e x p l a i n e d on the b a s i s 119 of d i f f e r e n t i a l s a t i a t i o n r a t e . An experiment w i t h s u f f i c i e n t c o n t r o l to r u l e out the e f f e c t of s a t i a t i o n i s n e c e s s a r y to e s t a b l i s h whether domestic s t o c k r e j e c t h a t c h e r y food l e s s f r e q u e n t l y than w i l d s t o c k . I f such a d i f f e r e n c e e x i s t s , i t i s p r o b a b l y s l i g h t . A l t h o u g h Experiment 13 d i d not r e f u t e the n u l l h y p o t h e s i s , i t d i d demonstrate some c h a r a c t e r i s t i c s of f e e d i n g b e h a v i o r . I t showed t h a t domestic t r o u t ate more t h a n w i l d , and t h a t f r y of b o t h s t o c k s ate more l i v i n g than dead prey and more when p a r t of a group. As mentioned b e f o r e , domestic s t o c k grows b e t t e r under h a t c h e r y c o n d i t i o n s ; the f i n d i n g t h a t they a l s o ate more o f f e r s a p a r t i a l e x p l a n a t i o n . The t e s t s w i t h moving and s t a t i o n a r y prey models suggest t h a t movement, and n o t some o t h e r p r o p e r t y , was mainly r e s p o n s i b l e f o r the g r e a t e r consumption of l i v i n g p r e y . The f i n d i n g that young of both s tocks ate more when p a r t of a group i s r e m i n i s c e n t of one k i n d of s o c i a l f a c i l i t a t i o n observed by others ( Y e l t y , 1934; Harlow and Y u d i n , 1933). Experiment 13 a l s o showed t h a t copepoda and c l a d o c e r a were net randomly d i s t r i b u t e d among the i n d i v i d u a l s , even though the two foods were dead a n i j l i s p e r s e d on the bottom of the a q u a r i a . T h i s f i n d i n g suggests the e x i s t e n c e of e i t h e r i n n a t e d i f f e r e n c e s i n s t i m u l i which e l i c i t f e e d i n g or a k i n d of c o n d i t i o n i n g which o c c u r r e d more r a p i d l y than t r a i n i n g b i a s . Of the two p o s s i -b i l i t i e s , the l a t t e r seems the more l i k e l y . The s t o c k s may d i f f e r i n other ways which would r e s u l t i n t e n d e n c i e s to eat d i f f e r e n t k i n d s . o f f o o d i n " n a t u r a l " 120 s i t u a t i o n s . Any d i f f e r e n c e i n searching technique, f e e d i n g rhythm, capture a b i l i t y , or sub-habitat occupied, might r e s u l t i n d i f f e r e n t kinds of food being eaten. There i s evidence that such mechanisms operate to produce d i f f e r e n c e s i n food eaten by d i f f e r e n t species of salmonids l i v i n g i n the same h a b i t a t . D i f f e r e n t salmonid species l i v i n g a l l o p a t r i c a l l y i n s i m i l a r lakes eat s i m i l a r food, whereas sympatric species eat l e s s s i m i l a r food ( N i l s s o n , 1955, 1965; Andrusak, MS 1968; S w i f t , 1970). In a lake, D 0 l l y Varden char e x p l o i t e d benthic organisms, and c u t t h r o a t t r o u t e x p l o i t e d mainly surface organisms (Andrusak, MS 1968). Schutz (MS 1969) d i s c o v e r e d some mechanisms accounting f o r such d i f f e r e n c e s . Yhen brought i n t o the l a b o r a t o r y , D o l l y Varden could capture benthic organisms at much lower l i g h t i n t e n s i t i e s . Moreover, they were more e f f e c t i v e i n s i f t i n g organisms from substratum and continued to search the substratum longer than c u t t h r o a t t r o u t . Yhen prey were presented on both the surface and the bottom, c u t t h r o a t e x p l o i t e d the surface organisms more r e a d i l y than D o l l y Varden. Presumably such d i f f e r e n c e s have a p a r t l y genetic b a s i s . I t i s conceivable t h a t s i m i l a r d i f -ferences e x i s t among i n d i v i d u a l s of a t r o u t s p e c i e s . In the threespine s t i c k l e b a c k , f o r i n s t a n c e , t h e r e are two morphological types l i v i n g i n Paxton Lake, B. C. (G. L. Larson, pers. comms). One type feeds mainly on plankton, and the other mainly on benthic organisms. The d i f f e r e n c e s were apparent i n both the lake and the l a b o r a t o r y . Genetic 121 d i f f e r e n c e s are thought to produce the d i f f e r e n c e s i n morph-o l o g y , h a b i t a t s e l e c t i o n , and t h e r e f o r e , the d i f f e r e n c e s i n k i n d of f o o d ea ten . I n c o n c l u s i o n , rainbow t r o u t d i d not respond d i f f e r e n -t i a l l y to v i s u a l or chemical s t i m u l i of food commonly eaten by t h e i r p a r e n t s . T h i s presumably means t h a t they d i d not r e c o g n i z e s p e c i f i c v i s u a l or c h e m i c a l c h a r a c t e r i s t i c s of p a r e n t a l f o o d s . T h i s does not mean that there were no g e n -e t i c d i f f e r e n c e s between them, nor w i t h i n rainbow t r o u t p o p -u l a t i o n s , which c o u l d produce d i f f e r e n c e s i n food s e l e c t i o n by d i f f e r e n t i n d i v i d u a l s . 122 BIBLIOGRAPHY A l i , M. A . 1959. The o c u l a r s t r u c t u r e , r e t i n o m o t o r , a n d p h o t o - b e h a v i o u r a l responses of j u v e n i l e P a c i f i c salmon. Can. J . Z o o l . 37: 965-996. Andrusak, H . 1968. I n t e r a c t i v e s e g r e g a t i o n between a d u l t D o l l y Varden ( S a l v e l i n u s malma) and c u t t h r o a t t r o u t (Salmo c l a r k i c l a r k i ) i n s m a l l c o a s t a l B r i t i s h Columbia l a k e s . M . S c . t h e s i s , Department of Z o o l o g y , U n i v e r s i t y of B r i t i s h C o l u m b i a . 76 p . B a r n e t t , S. A . 1963. 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