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A comparative study of the behaviour of two sympatric species of freshwater sculpins, Cottus asper Richardson… Fenwick, Julie M. 1968

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A COMPARATIVE STUDY OF THE BEHAVIOUR :_ OF TWO SYMPATRIC SPECIES OF FRESHWATER SCULPINS, Cottus asner Richardson AND Cottus a leut i cus G i l b e r t , IN RELATION TO THEIR DIFFERENCES IN MICROHABITAT . by J u l i e M. Fenwick B . S c . , M c G i l l Univers i ty , 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Zoology We accept t h i s thes i s as conforming to the required standard THE UNIVERSITY O F BRITISH COLUMBIA December, 1968 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y of B r i t i s h Columbia, I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and Study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department of ZOOLOGY The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date Dec, 19. 1968 ABSTRACT The behaviour of two sympatric species of scu lp ins , Cottus  asper and Cottus a l eut i cus , which occupy d i f f erent microhabi-ta t s , was studied by the comparative method. The aim of the study was to determine some of the important behavioural adap-ta t ions to the d i f ferences i n the ir microhabitats . C. asper occurs i n areas of slov; current and fine sub-s trate and G. a leut i cus i n areas of fast current and coarse sub-s t ra te . The posture, or i en ta t ion to the current , and locomotary and feeding behaviour of the species were examined i n the l a -boratory under d i f f e r e n t condit ions of current and substrate . C. asper responds to a current by l y i n g f l a t on the sub-s t r a t e . C. a l eut i cus also exhib i t s th i s posture on sand, but on a gravel substrate, r a i s e s the body, by spreading the pec-t o r a l f i n s . C. a leut icus adopts a p a r a l l e l or i en ta t ion to the current more frequently than a broadside or i en ta t ion , but C. asper "prefers" the broadside p o s i t i o n . However, both species assume the broadside pos i t i on more frequently on sand than on gravel , and the p a r a l l e l or i en ta t ion more frequently on gravel than on sand. C. asper i s a much poorer swimmer than C. a leut icus , es-p e c i a l l y i n a current . C. a leut icus i s much more act ive than C. asper at a l l times of day and under a l l condit ions of cur-rent tested. i i C. asper i s a l u r k i n g predator and takes food from the sur-face of the substrate . C. a leut icus i s a more act ive feeder, and feeds by swimming'to the water surface, by . tak ing food from the substrate surface and by foraging i n the crevices of the grave l . From laboratory observations i t appears that C. a leut icus r e l i e s on sight i n food detect ion to a greater extent than does C. asper. The f indings of t h i s study were compared with f i e l d obser-vations and with previous studies of other c o t t i d species . I t was concluded from t h i s that C. a l e u t i c u s 1 posture, or i en ta t ion to the current , and locomotory and feeding behaviour are a r e -f l e c t i o n of a more act ive way of l i f e and are re la ted to the spec ia l problems of l i f e i n a strong current . C. asper, how-ever, i s t y p i c a l , both i n behaviour and morphology, of bottom-dwel l ing, sedentary f i s h , of rec lus ive habi t s . i i i ACKNOWLEDGMENT The author wishes to express her sincere gratitude to Dr . N . R . L i l e y for h i s f i n a n c i a l assistance and advice throughout the course of th i s study and for h i s help i n the preparation of t h i s manuscript. I would also l i k e to thank Dr. D. McPhail and Dr. G . G . E . Scudder for t h e i r he lp fu l suggestions. To a l l my fel low graduate students, i n p a r t i c u l a r Mr. B . H . Seghers and Mr. D . L . Kramer, who helped to c o l l e c t spec i -mens, my sincere thanks. Thanks are also due to Mrs. Caren Jones for typing the manuscript and to Mr. Eugene McCulloch for h i s help i n con-s t r u c t i n g apparatus. F i n a l l y , spec ia l thanks are due to my husband, Jim, for h i s help and encouragement throughout the course of t h i s study. I v TABLE OF CONTENTS Page ABSTRACT. . . . i ACKNOWLEDGMENTS . . i i i TABLE OF CONTENTS . i v LIST OF TABLES. v i LIST OF FIGURES . . • v i i i INTRODUCTION. . . . 1 MATERIALS AND METHODS 5 Descr ipt ion of Species • . . 5 C o l l e c t i n g and Holding Condit ions . . 5 Flow Tank . . . . . . . . . . . . . . . . . 7 Times of Observations . . . . . 9 RESULTS . .11 Or ienta t ion With Respect to the Current . . . . . . . . .11 A. Observation. 11 B. Method .11 C. Results . 12 Stance 20 A. Observation . 2 0 B. Method . 2 3 C. Resul ts . . • •: • . 2 3 Movement i n Response to Current 26-A. Observation . 2 6 B. Method . 27 C. Results .' . . . . 2 9 V Feeding Behaviour . . . . . . . . . . .32 A. Observation. . . . . . . . .32 B. Method .34 C. Resul t s . ." . . .36 DISCUSSION. . . ' . . . . . . . . . .38 Discuss ion of Results .38 General Discussion . .41 SUMMARY 47 BIBLIOGRAPHY. . .49 APPENDIX. .52 A. Adaptab i l i t y to Laboratory Condit ions . . . . . . .52 B. Influence on Numbers on Behaviour :52 C. Response to Unfamil iar St imul i .54 D. Crypt i c Colourat ion . ". . .55 v i LIST OF TABLES Page I The frequency with which C. asper and C. a l eut i cus faced " in to ," "away" from and "broadside" to the current on a sand sub-s tra te , at four current speeds . 13 II The frequency with which C. asper and C. a l eu t i cus faced " into ," "away" from and "broadside" to the current on a gravel substrate, at four current speeds . . 1 4 I I I The frequency with which C. asioer and C . a l eu t i cus faced i n three d i r e c t i o n s at four current speeds on a sand substrate . . . . . . 1 5 IV The frequency with which C. asper and C. a l eut i cus faced i n three d i r e c t i o n s at four currents speeds on a gravel substrate 16 V The frequency v/ith which C. asper and C. a l eut i cus faced i n three d i r e c t i o n s at four current speeds on a sand substrate . . . . . . 1 8 VI The frequency v/ith which C. asper and C. a l eut i cus faced i n three d i rec t i ons at four current speeds on a gravel substrate 19 VII Postures assumed by C. asper on sand and gravel substrates under two condit ions of current .24 VIII Postures assumed .by C_. a leut icus on sand and gravel substrates under two condit ions of current „ 25 v i i Page IX T o t a l number of inches moved by C. asper  a n c * C». a leut icus i n f i f t een minutes at four current speeds „ . . . . . . 30 X Mean number of inches moved by C. asper and C. a l eu t i cus i n f i f t een minutes at four current speeds . . . . . . . 3 1 XI A b i l i t y to detect food by chemical senses . . . . . 3 7 XII Summary of r e s u l t s of substrate /current v e l o c i t y choice experiments (G. Taylor , 1 9 6 6 ) 4 2 XIII E c o l o g i c a l data on the areas of the L i t t l e Campbell River from which C. asper and C. a l eut i cus were c o l l e c t e d . 43 v i i i LIST OF FIGURES Page 1 The flow tank and current producing apparatus used i n locomotion, o r i e n t a t i o n , and posture experiments . . . 8 2 Four postures of C. asper and C. a leut icus . . . . . .22 3 The methods used to swim i n a current . . . . . . . . . .28 k The Y trough used for food detect ion experiments .35 1 INTRODUCTION This thes i s i s concerned with a comparative study of the behaviour of two c lose ly re la ted species of freshwater scu lp ins , family Cott idae . Cottus asper and Cottus a l eut i cus are known to d i f f e r i n t h e i r microhabitats v/ith respect to the nature of the substrate and the current v e l o c i t y (Taylor , 1966) . The present study was a comparison of the behaviour of these species under d i f f e r e n t condit ions of current and substrate to determine which are the important behavioural adaptations to these d i f -ferences i n microhabitat . One of the d i s t i n g u i s h i n g features of the family Cottidae i s the absence of a swimbladder. As would be expected from t h i s , the group as a whole i s benthic . Cot t ids occur over rubble (Bai ley , 1952), gravel (Simon and Brown, 1943)j and mud and sand (Taylor , 1966). They are found i n pools (Taylor , 1966), i n slow streams (Smyley, 1957), and i n torrents ( C a r l et a l . , 1951), and r i f f l e s (Bai ley , 1952) . Each species i s commonly co l l ec ted i n assoc iat ion with a spec i f i c substrate type and a c e r t a i n current v e l o c i t y . I t has been suggested (Bai ley , 1952) that the p r i n c i p a l factor governing habitat choice, at l eas t i n the spawning sea-son, i s the nature of the substrate , and that a given current speed i s only apparently selected owing to i t s assoc iat ion with c e r t a i n substrate types (Zarbock, 1 9 5 D » Ba i l ey (1952) found that although C. b a i r d i apparently chose i t s spawning s i t e s on the bas is of substrate type, most of the nests were found i n 2 areas where the surface v e l o c i t y was quite h igh . However, water movements ins ide the nest i t s e l f were rather gentle . Another common feature of the freshwater sculp ins i s that they usual ly occur i n groups of two or more species, each one of which i s more frequent i n some parts of the r i v e r or stream than i n others, according to the d i s t r i b u t i o n of current speed and substrate type (Straskaba et a l . , 1966; Ba i l ey , 1952; Smyley, 1957; Tay lor , 1 9 6 6 ) . Coastal B r i t i s h Columbia i s com-p a r a t i v e l y "Impoverished," i n that only two species, the p r i c k l y s c u l p i n , Cottus asper Richardson, and the Aleut ian s c u l p i n , Cottus a leut i cus G i l b e r t , are present. This area therefore presents a somewhat s impl i f i ed s i t u a t i o n , amenable to study. Sculpins a l l over the northern hemisphere appear to have rather s i m i l a r d i e t s , c h i e f l y cons i s t ing of bottom dwell ing i n -vertebrates (Smyley, 1957; Bond, 196ft; Northcote, 195ft) . They eat organisms within c e r t a i n s ize ranges that depend on the mouth s ize of the s c u l p i n . The s ize of food taken therefore d i f f e r s not only between species, but also during the l i f e t i m e of a s ingle i n d i v i d u a l . Cottus asper and Cottus a leut i cus are sympatric i n the L i t t l e Campbell River of southwest B r i t i s h Columbia. C o l l e c -t i o n studies (Taylor , 1966) ind ica te that they d i f f e r i n t h e i r microhabitats , C. asper i n h a b i t i n g areas of slov/ current and f i n e l y textured substrate, and C. a l eut i cus occurr ing i n areas of swift current and coarse substrate . These microhabitats overlap to some extent, and where C. asper i s scarce or absent, 3 C. a l eut i cus may occupy C. asper type habi ta ts . Laboratory studies (Taylor , 1966) ind icate that these species exercise some degree of s e l e c t i v i t y i n t h e i r environ-ment with regard to substrate type and current v e l o c i t y . In the laboratory C. asper and C . a leut icus tend to choose current and substrate condit ions that resemble those occurring i n t h e i r natura l hab i ta t . However Taylor did not examine the animals' behaviour once the choice-was made to determine i f the species' behaviour d i f f e r e d i n a way that could be corre lated with the substrate and current type that they had chosen. I t seems l i k e l y that these di f ferences i n microhabitat would be r e f l e c t e d i n the everyday behaviour of the scu lp ins . Consequently C. asper and C. a leut i cus were observed i n l abora -tory s i tua t ions i n which current speed and substrate type were v a r i e d . Their behaviour i n these various circumstances was noted, and experiments were then conducted to examine further any d i f ferences which these observations had i n d i c a t e d . The feeding behaviour of C. asper and C. a l eut i cus was also studied, as i t appeared to be re la ted to the di f ferences i n the behaviour of the two species i n current condi t ions . The present study was, i n a sense, a departure from "clas-s i c a l " vertebrate ethology, i n that the behaviour considered was not a form of s o c i a l behaviour, but the means used by the i n d i v i d u a l to meet the problems of food gett ing and locomo-t ion that the environment presents d a i l y . Throughout t h i s study the comparative method was chosen as the most f r u i t f u l means of d iscover ing the s ign i f i cance of behavioural d i f ferences as eco log ica l adaptations (Lack, 1965). 5 MATERIALS AND METHODS Descr ipt ion of Species C. asper and C. a leut i cus are rather s i m i l a r i n appearance (see C a r l et a l . , 1 9 5 9 , for complete d e s c r i p t i o n ) . However, they do d i f f e r morphological ly i n several respects that have a bearing on t h e i r behaviour i n d i f f erent current and substrate condi t ions . C. asper i s the l arger species, a t t a i n i n g a length of up to 1 5 0 mm. A few i n d i v i d u a l s may be up to twice t h i s s i ze . C. a l e u t i c u s , however, r a r e l y exceeds 1 0 0 mm i n length . C. asper has a very large , broad head and mouth r e l a t i v e to body s i ze , but C. a l eut i cus has a mouth and head more i n proport ion to the re s t of i t s body. C. asper's body i s somewhat dorso-ventra l ly compressed, and the width of the body decreases markedly from head to t a i l . C. a l eut i cus i s more c y l i n d r i c a l i n shape and has a l e s s pronounced tapering from the anter ior to the pos-t e r i o r of the body. C o l l e c t i n g and Holding Conditions C. asper and C t | a l eut i cus were co l l ec ted from the L i t t l e Campbell River i n a seine net ( 2 , 4 m x 1 . 6 m x 3 mm mesh) equipped with aluminum poles and heavy weights. R o l l e r type leads were used as these e f f e c t i v e l y s t i r r e d up the substrate and disturbed the scu lp ins . At times the seine was held s ta -t ionary while the substrate was disturbed by someone splashing downstream towards the net. However, best result's were usual ly 6 obtained by taking short, deep dr ives i n deep pools , from the middle of the streambed towards the shore, or by making long sweeps upstream i n shallower water. Large C. a leut i cus were sometimes c o l l e c t e d by jabbing the aluminum poles under the overhanging banks i n r i f f l e areas and suddenly l i f t i n g the net with a scooping motion. The fish'were held i n four outdoor troughs (7'2" x 16" x 8") with running dechlorinated water and a i r hoses. Some f i s h were also held i n a small unheated hut, i n two plywood tanks (40" x 12" x 1 8 £ " ) and i n one metal tank (8« x 1 0 £ " x 8v") with running dechlorinated water and a i r hoses. The plywood tanks were each equipped with three p l ex ig la s s windows on one s ide, and were used to observe the general behaviour of the f i s h . These tanks had gravel substrates of varying depths. The gra-v e l at the deep .water end of the tank was 2 3/4" th ick , and the depth of the substrate gradual ly increased u n t i l at the shallow water end the gravel was 10?" to 11 3/4" th i ck . Both species were held at various times i n bare troughs, over grave l , or over sand. The indoor tanks were provided with "hides" i n the form of halved clay flowerpots. The outdoor tanks were p a r t i a l l y covered to give the f i s h a refuge. The temperatures i n these tanks f luctuated from 0°C i n the month of February to l 6 ° C i n J u l y . C. a l eut i cus i s not as to lerant of high temperatures as C. asner, and i s usual ly not co l l ec t ed i n areas with a seasonal high temperature of greater than 15°C (Taylor , 1966). Consequently, most of the C. 7 aleut icus were kept i n the indoor troughs as the summer tempera-ture i n the hut could be kept lower than outdoors. A l l f i s h were exposed to the natural seasonal and d a i l y l i g h t v a r i a t i o n s . The co t t ids were fed thawed, concentrated brineshrimp. The diet was varied with small f i s h , such as guppies, gouramis and small g o l d f i s h . Feeding times were unscheduled, and at i r r e g u l a r i n t e r v a l s they received no food for a day or two. This was done not only to prevent the f i s h from developing a conditioned a c t i v i t y cyc l e , but also because i t was found that the co t t ids ate more i f they were deprived of food one or two days i n every v/eek. A l l tanks were treated regu lar ly with one or two drops of a 1% so lut ion of malachite green, as a fungic ide . Flow Tank For several experiments i t was necessary to produce cur-rents of several d i f f erent speeds. A flow tank was constructed ( 8 1 x 20-1-" x of plywood and £» p l e x i g l a s . This tank ( F i g . 1) consisted of two channels separated by a plywood par-t i t i o n (6'2" x x H i " ) . One channel (5*8" x 9 l " x H i " ) had a p l ex ig las wall through which the f i s h were observed, and the other (81 x 9i"" x H i " ) was for the r e c i r c u l a t i o n of water. The ends of the viewing channel were screened and at times the f i s h were res tra ined i n the middle port ion of the channel i n a wire fence ( 2 3 " x 9 i" x 151"). A small submersible pump ( L i t t l e Giant model 1,115 vo l ts ) was placed i n the r e c i r c u l a t i o n channel to provide a constant 8 Figure 1. The flow tank and current producing apparatus used i n locomotion, o r i e n t a t i o n , and posture experiments. s p e e d t r o l o v e r f l o w p i p e 0/ w a t e r t ap ~~~~~^=S d r i l l p l e x i g l a s w i n d o w d r i v e s h a f t i m p e l l e r b l a d e 9 slow current of l e s s than 6 cm/sec. This was current 1, equi-valent to T a y l o r ' s (1966) "noncurrent." Other current condit ions were produced by a 5" impel ler blade mounted i n the water behind the screen at one end of the viewing channel. This was connected by a rubber insulated driveshaft to a heavy duty i n d u s t r i a l d r i l l (Rockwell 7 5 8 R ; r") suspended outside the tank. The d r i l l speed was regulated by a speedtrol (Model SC1000; C . C . Industr ies I n c . , Ph i lade lph ia , P a . ) . With t h i s apparatus surface v e l o c i t i e s of 13, 20, and 25 cm/sec were obtained (currents 2, 3 and L\.). Various quant i t ies of a 1% so lut ion of methylene blue were placed i n t h i s system to study the pattern of the current . The current appeared to be rather uniform from the water surface to the surface of the substrate, except i n the area immediately i n f ront of the im-p e l l e r blade, where there was much turbulence. Times of Observations The f i s h used i n t h i s study were held e i ther i n outdoor troughs or i n a small hut which was panelled i n f ibreg las sheets which admitted d i f fuse natural l i g h t . They were therefore ob-served under natural dayl ight condi t ions . I t soon became apparent that both species-were more act ive at some times of day than at others. Both C. asper and C. a leut i cus were rather act ive u n t i l approximately 11 am, a f ter which a c t i v i t y was main-tained at a lower l e v e l u n t i l about 1 pm, and there was then very l i t t l e a c t i v i t y u n t i l early evening, about dusk.- The C. asper were l e s s act ive at a l l times of day than the C. 1 0 a leu t i cus , and they remained motionless under t h e i r flowerpot "hides" throughout most of the afternoon. It was suggested that perhaps t h i s low l e v e l of daytime a c t i v i t y i n C. asper was compensated for by a higher nighttime a c t i v i t y . Experiments were therefore conducted, using appara-tus designed by Byrne ( 1 9 6 8 ) , to see i f the a c t i v i t y cycles of the two species d i f f e r e d r a d i c a l l y i n shape. The locomotary ^ a c t i v i t y of four f i s h of each species was recorded automatical ly . Recordings were made continuously of C. asper for ten days and ° f C« a leut icus for twenty-one days. I t was discovered that i n both species there was a s l i g h t l y higher l e v e l of a c t i v i t y during most of the night than during the day, and a b r i e f burst of a c t i v i t y short ly af ter dusk. Both species were more act ive i n the ear ly morning than i n the l a t e afternoon. I t was therefore decided that experiments should be con-ducted i n the early morning to ensure that' the f i s h would be observed at a time when they were normally ac t ive and under l i g h t condit ions sui table for observation. 11 RESULTS Orientat ion With Respect to the Current A. Observation When C. asper and C. a leut i cus were observed at res t under current condit ions , i t was noted that they al igned themselves i n a rather spec i f i c manner with respect to the d i r e c t i o n of flow of the current . On a l l but a very few occasions, they could be c l a s s i f i e d as e i ther p a r a l l e l to or broadside to the d i r e c t i o n of flow. Further , i t appeared that the two species d i f f e r e d i n the i r preference for one of these pos i t ions . The or i enta t ion responses with respect to the current were so consistent that i t was thought that they must be of cons i -derable importance to the animals. Experiments were therefore conducted to determine the d i f ferences i n the frequencies of the pos i t ions adopted by the tv/o species. I f one can demonstrate di f ferences i n the response of two sympatric species to changes i n cer ta in environmental parameters one may then speculate on the s igni f icance of these d i f ferences as eco log ica l adaptations. B. Method To f ind the "preferred" d i r e c t i o n of or i enta t ion with r e -spect to the current, that i s , the one most frequently assumed, ten f i s h of one species v/ere placed i n a bottomless wire cage i n the middle port ion of the flow tank, where a current of uniform ve loc i ty could be maintained. They were then exposed to a current of constant speed for f i f t een minutes. At the end 12 of t h i s time the number of f i s h f a c i n g " i n t o , " "away" from and "broadside" to the current source was recorded. Three subse-quent recordings were made at i n t e r v a l s of f i v e minutes.. Each group of ten f i s h was t e s t e d at four current speeds; l e s s than 6 cm/sec ("noncurrent"), and 1 3 , 2 0 , and 25 cm/sec. Forty f i s h of each species were tes t e d on a gravel substrate, and t h i r t y of each species on sand. C. R e s u l t s I n a n a l y s i n g these data, i t was thought best to consider the p a r a l l e l alignment as two c a t e g o r i e s , " i n t o " and "away," as there would be a considerable d i f f e r e n c e i n the p a t t e r n of cur-rent flow around animals i n these p o s i t i o n s . The data obtained on sand and g r a v e l substrates were t e s t e by two analyses of variance (Tables I and I I ) . In both cases the only one of the c o n d i t i o n s that showed a s i g n i f i c a n t d i f -ference at p<0.01 was the d i r e c t i o n faced (D). The i n t e r -a c t i o n s species x d i r e c t i o n (S x D) and d i r e c t i o n x current (D x C) were a l s o s i g n i f i c a n t at p< 0 . 0 1 . In n e i t h e r case was the second order i n t e r a c t i o n species x d i r e c t i o n x current s i g n i f i c a n t . The means were compared by the Student-Newman-Keul t e s t . As can be seen from Tables I I I and IV, C. a l e u t i c u s assumed the p a r a l l e l alignment more f r e q u e n t l y than the broadside, while C. asper d i d the reverse. At no time d i d G. a l e u t i c u s show a s i g n i f i c a n t preference f o r the "broadside" over the " i n t o " p o s i t i o n . 13 TABLE I The frequency with which C. asper and C. a leut icus faced " into ," "away" from and "broadside" to the cur-rent on a sand substrate, at four current speeds. SOURCE SS df MS F Species (S) 0 . 0 1 __— Direc t ion (D) 1157.25 2 578.625 186.89* Current (C) 0 . 0 3 S x D 382.58 2 191.29 61.786* S x C 0 . 0 3 D x C 53.91 6 8.985 2 .902* S x D x C 36.89 6 6.148 1.986 Error 817.37 264 3.096 Tota l 2448.0 287 ^s ign i f i cant at p<0.01. 14 TABLE II The frequency with which C. asper and C. a leut icus faced " into ," "away" from and "broadside" to the current on a gravel substrate, at four current speeds. SOURCE SS MS F Species (S) 0 . 0 1 _ _ _ D i r e c t i o n (D) 265.85 2 132.925 65.513* Current (C) 0 . 0 3 S x D 237.95 2 , 118.975 58.637* S x C 0 . 0 3 D x C 57.80 6 9.633 4.748* S x D x C 15.33 6 2.556 1.259 E r r o r 730.4 360 2.029 T o t a l 1307.33 383 - — *s ign i f l eant at p<0.01. 15 TABLE III The frequency with which C. asper and C. a leut icus faced i n three d i r e c t i o n s at four current speeds on a sand substrate. Data are arranged to compare " i n -to ," "away" and "broadside" or ienta t ions at each of four current speeds. Tabulated values are means ob-tained from 30 f i s h of each species, observed 10 at a time, C. asper Current Into Away Broadside 1 2.75 1.0 6.25 2 1.17 0.83 8 . 0 3 1.25 1.0 7.75 4 1.0 0.75 8.. 25 C. a l eut i cus Current Into Away Broadside 1 3.67 2.58 3.75 2 4 . 0 1.58 4 .42 3 3.83 1.08 5.08 4 4 . 5 0.83 4.67 Means joined by dotted l i n e s are s i g n i f i c a n t l y d i f f erent at p < 0 . 0 5 by the Student-Newman-Keul tes t . 16 TABLE IV The frequency with which C . asper and C. a leut i cus faced i n three d i rec t i ons at four current speeds on a gravel substrate . Data are arranged to compare " into ," "away" and "broadside" or ientat ions at each of four current speeds. Tabulated values are means obtained from 40 f i s h of each species , observed 10 at a time. C. asper Current Into Away Broadside 1 2.25 2.75 5.0 2 2.69 1.81 5.5 3 2.38 1.56 6.06 4 1.31 2.88 5.81 C. a leut i cus Current 1 2 Into 3.75 4 . o Away Broadside 3.13 3.13 3.25 2.75 3 4 3.56 3.13 2.63 2.94 3.81 3.94 Means joined by dotted l i n e s are s i g n i f i c a n t l y d i f f erent at p < 0 . 0 5 by the Student-Newman-Keul tes t . . 17 C. asper behaved i n much the same manner on sand as on grave l , except that the preference for the "broadside'" p o s i t i o n was more pronounced on sand. C. a l eu t i cus , however, showed considerable d i f ferences i n t h i s behaviour on gravel and on sand. On a gravel substrate no one p o s i t i o n was preferred at e i ther current 1 or current 4. At current 2 there was a s i g n i f i c a n t l y greater number of a n i -mals that assumed the "into" p o s i t i o n . At current 3 "broad-side" was more frequent than "away," but not more than " in to ." On a sand substrate C. a leut i cus showed no preference at cur-rent 1, but at the other three current speeds "broadside" and and "into" were both more frequent than "away," although no s i g n i f i c a n t dif ference could be found between "into" and "broad-s ide ." The "away" category does not appear to follow an eas i l y describable pat tern . I t was much more frequent i n C. a leut icus than i n C. asper, r e f l e c t i n g C. a l eu t i cus ' o v e r a l l greater pre-ference for the p a r a l l e l alignment. At no time, however, was i t more frequent than the "into" pos i t ion i n C. a l eu t i cus . C. asper adopted the "away" pos i t i on more frequently than the "into" at high current speeds on g r a v e l . As can be seen from Tables V and VI , current speeds had very l i t t l e ef fect on the frequency with which C. a leut icus assumed any p o s i t i o n . No s i g n i f i c a n t d i f ferences were detec-table by the Student-Newman-Keul tes t . C. asper, however, d id respond to changing current speed with a change i n p o s i t i o n . On a gravel substrate the frequency 18 TABLE V The frequency with which C. asper and C. a leut i cus faced i n three d irec t ions~at four current speeds on a sand substrate . Data are arranged to show the effect of four current speeds on a s ingle or i en ta -t i o n . Tabulated values are means obtained from 30 f i s h of each species , observed 10 at a time. C. asper > Current 1 2 3 4 D i r e c t i o n Into 2.75 1.17 1.25 1.0 Away 1.0 0.83 1.0 0.75 Broadside 6.25 8 . 0 7.75 8.25 C. a l eut i cus Current 1 2 3 4 D i r e c t i o n Into 3.67 4. o 3.83 4 . 5 Away 2.58 1.58 1.08 0.83 Broadside 3.75 4 . 4 2 5.08 4.67 Means joined by dotted l i n e s are s i g n i f i c a n t l y d i f f erent at p < 0 . 0 5 by the Student-Newman-Keul tes t . 19 TABLE VT The frequency with which C. asper and C. a leut icus faced i n three d i r e c t i o n s a t ' four current speeds on a gravel substrate . Data are arranged to show the effect of four current speeds on a s ingle o r i e n t a -t i o n . Tabulated values are means obtained from 40 f i s h of each species , observed 10 at a time. C. asper Current 1 2 3 4 D i r e c t i o n Into 2.25 2.69 2.38 1.31 Away 2.75 1.81 1.56 2.88 Broadside 5.0 . 5.5 6.06 5.81 C. a l eu t i cus Current 1 2 3 4 D i r e c t i o n Into 3.75 4 . 0 3.56 3.13 Away 3.13 3 .25 2.63 2 . 9 4 . Broadside 3.13 2 .75 3.81 3 .94 Means joined by dotted l i n e s are s i g n i f i c a n t l y d i f f erent at p < 0 . 0 5 by the Student-Newman-Keul t e s t . 20 of the "into" category decreased at the highest current speed used, (ft), and t h i s was s i g n i f i c a n t l y d i f f eren t from the f r e -quency at current 2. The frequency of the "away" category at f i r s t decl ined and then increased with current speed, s i g n i f i -cant ly d i f f e r e n t means being obtained between currents 1 and 3> and currents 3 and ft. The "broadside" category remained at about the same frequency at a l l current speeds. On a sand substrate the behaviour of C. asper was somewhat d i f f e r e n t . There was a decreasing frequency of the "into" category, the d i f ferences between currents 2 and 3 being s i g n i -f i c a n t . The "away" category remained about the same; rather i t was the "broadside" frequency which changed. This category was of a s i g n i f i c a n t l y lower frequency at current 1, than at any of the other three current speeds. Stanc e A. Observation Ear ly i n the course of t h i s study i t was noticed that C. asper and C. a leut i cus had several c h a r a c t e r i s t i c postures with regard to the pos i t i on of head arid body and the degree of ex-tension of the f i n s . There appeared to be a di f ference i n the frequencies v/ith which these "stances" were assumed by the two species . Further , i t appeared to be poss ible to corre la te a given condit ion of substrate and current with a stance for each species . The most common posture assumed by C. asper when at res t on a sand substrate was to l i e with the b e l l y pressed f l a t against 21 the sand, the head h o r i z o n t a l , the dorsa l f in s somewhat ex-tended and the pec tora l , pe lv ic and caudal f in s fo lded. C. a l eut i cus also assumed t h i s posture on sand, but on a gravel substrate they-, more frequently extended the pectora l f i n s , thus l i f t i n g the body out of the hollows between the stones. Under many condit ions of current and substrate C. a l eut i cus assumed the "head down" or "head up" pos i t ions ( F i g . 2) , i n which the body was i n c l i n e d at an angle to the substrate . The "head up" pos i t i on was about as frequent as the h o r i z o n t a l , but the "head down" was usual ly only observed when the animal was foraging for food among the rocks , or i f i t was i n an area of extreme turbulence. The dorsa l f ins of C. a l eut i cus were most often extended, although under some condit ions the folded posture was of equal frequency. When C. asper were placed on a gravel substrate they r e -tained t h e i r c h a r a c t e r i s t i c posture, so that they lay between -the stones. I t seemed l i k e l y that the stances assumed by the two species would make a considerable di f ference to t h e i r exposure to the current . Experiments were therefore conducted to de-termine di f ferences i n the frequencies of the various postures between the species . By comparing the stances of the animals i n a var ie ty of condit ions of current and substrate, one could speculate on the function of these postures. 22 Figure 2. Four postures of C. asper and C. a leut i cus a) head up b) head dovm c) pectoral f i n s expanded d) pec tora l f in s folded 23 B. Method To determine the stance most commonly assumed i n any given condit ion of substrate and current , f ive f i s h of one species were placed together i n the flow tank and exposed to one of two current condit ions , "noncurrent" ( l e ss than 6 cm/sec) and "cur-rent" (greater than 10 cm/sec). The f i s h were a c t u a l l y observed at three d i f f erent current speeds, but since there was no de-tectable d i f ference among these categories they were considered as one. Consequently there are three times as many recordings for "current" as "noncurrent." The pos i t i on of the head and body, and the degree of expansion of the dorsa l and pectoral f in s were noted. The pectora l f in s were not considered to be "expanded" i f they were merely fanned out f l a t against the sub-s t ra te , but only i f they.were held at an angle to the substrate ( F i g . 2). A t o t a l of /+73 recordings were made, f i f t een f i s h of each species being observed on sand, and f i f t een on grave l . Recor-dings were made for approximately f ive minutes at a time. C. Results The counts obtained were grouped according to a l t e r n a t i v e s , e . g . , "pectoral folded" ( p . f o l . ) and "pectoral extended" ( p . e x . ) . 2 A ser ies of X tes t s were then performed on the groups (Tables VII and V I I I ) . C. asper assumed the folded pos i t i on of the pectoral f ins under a l l condit ions tested, the most marked preference being shown with gravel and current (Table V I I ) . The hor izonta l 2ft TABLE VII Postures assumed by C. asper on sand and gravel sub-s trates under tv/o condit ions of current .1 Sand Gravel Current Noncurrent . Current Noncurrent Pectoral F ins Extended Folded , X 2 Preferred Dorsal F i n Extended Folded Preferred lft 33 7 . 6 8 p . f o l . 37 10 15.5 d. ex. 3 13 6.25 p . f o l , 10 6 l.o* 5 57 ft3.6 p . f o l . 55 7 37.16 d. ex. 0 15 15.0 p . f o l , 15 0 15.0 d. ex.. Head Horizontal Head Up Head Dov/n Preferred ftl 5 1 82.99 hor. lft 2 0 21.5 hor. 53 9 0 77.85 hor. lft 1 0 2ft. ft hor. ^ 6 cm/sec and >10 cm/sec. *not s i g n i f i c a n t at p < 0 . 0 5 . 25 TABLE VIII Postures assumed by C. a leut icus on sand and gravel substrates under two condit ions of c u r r e n t . 1 Sand Gravel Current Noncurrent Current Noncurrent Pec tora l F ins Extended Folded Preferred Dorsal F i n s Extended Folded X 2 Preferred 26 45 5.08 p . f o l . 59 12 31.11 d. ex. 3 17 9.8 p . f o l , 17 3 9.8 d. ex. 95 62 6.93 p. ex. 70 87 1.84* 80 5 66.18 p. ex. 59 26 12.81 d. ex. Head Horizonta l Head Up Head Down X 2 Preferred 58 12 1 61.79 hor. 13 7 0 12.70 hor. 77 75 5 64.3 39 ^2 4 31.51 h o r . / h . u . h . u . / h o r . <6 cm/sec and >10 cm/sec. *not s i g n i f i c a n t at p < 0 . 0 5 . 26 (hor.) pos i t i on of the body.was s i m i l a r l y great ly preferred , the preference being more marked i n current s i t u a t i o n s . The extended posture of the dorsa l f ins (d.ex.) was more frequent than the dorsa l folded pos i t i on ( d . f o l . ) at a l l times and t h i s preference was s i g n i f i c a n t except under sand and noncurrent condi t ions . C . a l eut i cus showed a much greater v a r i a b i l i t y of stance with changing condi t ions . Like C. asper, C. a leut icus showed' a d i s t i n c t preference for the pectora l folded posture on a sand substrate . However, when placed on gravel C. a l eut i cus much preferred the pec tora l extended posture. This was e spec ia l ly marked under noncurrent condi t ions . C . a l eu t i cus assumed the dorsa l extended posture with a-< greater frequency than the dorsa l folded i n three out of four cases. The exception was a small nons igni f icant preference for the dorsa l folded pos i t i on v/ith gravel and current . C. a l eut i cus favoured the hor i zonta l p o s i t i o n on sand, but on gravel the "head up" (h .u . ) pos i t i on occurred with equal frequency. Thus the two species behaved i n a very s i m i l a r manner on a sand substrate, but d i f f e r e d markedly i n the i r response to a gravel substrate . Movement i n Response to Current A. Observation It was observed that C. asper had great d i f f i c u l t y i n moving around i n the tank i n a .current of any magnitude, and that even i n noncurrent condit ions theyx_did not move about as much as C. a l e u t i c u s . C. a l eu t i cus i s a much better swimmer than C. asper. When attempting to move up or downstream i n the presence of a cur-rent , C. a l eut i cus kept close, to the substrate, p a r t i c u l a r l y i f i t was grave l , and moved i n a ser ies of short, rapid leaps ( F i g . 3 a ) . Using t h i s method, they had a remarkable a b i l i t y to main-t a i n t h e i r pos i t i on i n areas of extreme turbulence and to move upstream against a current capable of d i sp lac ing the grave l . C. asper attempted to move up or downstream by swimming up at an angle to the substrate ( F i g . 3 b ) . They were r a r e l y able to make any advances upstream i n any but the slowest currents , and t h e i r progress downstream was considerably hastened by the current . At times they appeared to be caught up by the current and swept he lp les s ly along u n t i l they reached the end of the tank farthest from the current source.. They were then able to r i g h t themselves by twis t ing the i r bodies u n t i l they were para-l l e l to the substrate and to sink to the bottom of the tank. Experiments were carr i ed out to detect a quant i tat ive d i f -ference i n the amount of movement up or downstream by the two species under various current condit ions . B. Method To test the amount of movement of the species, a bottomless wire cage was placed i n the middle port ion of the flow tank, where a current of constant speed could be maintained. The side wall of the tank, above the p l e x i g l a s window, was marked off i n 28 Figure 3» The methods used to swim i n a current a) C. a l eut i cus b) C. asper ^ d i r e c t i o n f l o w o f 29 inches along the length of the wire fence, so that the f i s h ' s p o s i t i o n could be determined at a glance through the window ( F i g . 1 ) . The pos ter ior margin of the f i r s t dorsa l f i n was. taken as a pos i t ion marker, to el iminate the ef fect of changes i n the d i r e c t i o n faced without any movement up or down stream. A s ingle f i s h was introduced at the midpoint of the cage, and i t s pos i t i on was recorded every three minutes for f i f t een minutes while i t was exposed to a current of constant speed. At the end of t h i s time the f i s h was removed and an i n d i v i d u a l of the other species and approximately the same s ize was s i m i -l a r l y tes ted . These f i s h were then discarded and another p a i r was tested at the same current speed. A t o t a l of forty f i s h were tested, ten under "noncurrent" condit ions ( less than 6 cm/sec) and t h i r t y at three d i f f erent current speeds ( 1 3 , 20 and 23 cm/sec). This experiment was conducted on a gravel substrate . C. Results The data from t h i s experiment v/ere tested by an analys i s of variance (Table I X ) . The species di f ference (S) v/as s i g n i f i c a n t at p<0.05 (F = 3 7 . 2 3 ) . Currents (C) and the species x currents i n t e r a c t i o n (S x C) v/ere not s i g n i f i c a n t . The species means v/ere compared by Tukey's w (Table X ) . C. a l eu t i cus showed a greater amount of movement than C. asper under a l l current condi t ions . The only s i g n i f i c a n t change i n amount of movement with, i n -creased current speed was a decrease i n movement by C. a leut icus 30 TABLE IX T o t a l number of inches moved by C. asper and C. a l eu t i cus i n f i f t e e n minutes at four current speeds. SOURCE SS df . MS F Species 70.33 1 70.33 3 7 . 2 3 * Current 1.77 3 0.59 0.31 S x C 4 . 2 3 1.4 0.74 E r r o r 60.48 32 . 1.89 Tota l 136.78 39 * s i g n i f i c a n t at p<0.05. 31 TABLE X Mean number of inches moved by C . asper and C. a l eu t i cus i n f i f t een minutes at four current"" speeds. Comparison of species means. Tukey's w = 2 . 3 6 0 9 . CURRENT Means for : C. asper 0 .1 0 . 2 0.1 0 .8 C. a l eut i cus 6 .8 5.5 7.8 4 . 8 Difference between the species 1 means 5 .7* 5 . 3 * 7.7* 4 . 0 * • s i g n i f i c a n t l y d i f f erent at s i g n i f i c a n t l y d i f f erent within a s ingle species p<0.05. . at p<0.05, when comparing at d i f f erent current speeds. 32 betv/een currents 3 and k (Table X ) . There i s a de f in i t e but nonsigni f icant increase i n movement by C. a l eut i cus between currents 2 and 3 . Feeding Behaviour A. Observation The superior swimming a b i l i t y and greater "alertness" of C. a l eut i cus i s re f l ec ted i n the species* feeding behaviour. The most common method i n both species i s to make short , h o r i z o n t a l darts across the bottom of the tank to seize food that i s l y i n g on the surface of the substrate or f l o a t i n g just above i t . Such "darts and grabs" have been reported i n another c o t t i d species by Smyley (1957). This behaviour i s sometimes d irected towards ined ib le objects , which are then spat out. C. asper r e l i e d almost exc lus ive ly on t h i s technique of food get-t i n g . The larges t i n d i v i d u a l s , which spent most of the daytime i n t h e i r hides , made b r i e f sor t i e s for food not far from the refuge, and quickly returned to i t . This method v/as used for small food items such, as brineshrimp, and also for small f i s h . A method that was very r a r e l y observed i n C. asper but quite often i n C. aleuticus-was swimming to the water surface to get food that v/as d r i f t i n g down. At times the f i s h ' s body would be almost perpendicular to the water surface, v/hile the pectoral f in s were used i n a fanning motion, and the body un-dulated. This a c t i v i t y usual ly las ted l e s s than t h i r t y seconds and i t v/as most commonly used when eating brineshrimp. C. a l eut i cus would quite frequently move over the grave l , 33 put t ing the head down i n the crevices i n the substrate to pick up food that had se t t l ed there. This foraging behaviour was used mainly i n obta ining brineshrimp, although occas ional ly a guppy that was small enough to s e t t l e between the stones was eaten i n t h i s way. C. a l eut i cus ate r e a d i l y whenever food was a v a i l a b l e , even during the times of day i n which t h e i r general l e v e l of a c t i -v i t y was somewhat reduced. C. asper l e ss often ate food as soon as i t was presented, and during t h e i r r e l a t i v e l y inac t ive per-iod they would usual ly eat only i f the food was deposited at the entrance of the hide. C. a l eut i cus seemed to r e l y on sight to a cer ta in extent ; i n obtaining i t s food. The dropper by which the brineshrimp I were introduced to the tank had only to appear above the water surface to set of f a burst of a c t i v i t y i n the f i s h ; i n p a r t i c u -l a r , swimming to the water surface beneath the dropper. C. asper were observed to r o l l t h e i r eyes up and to follow the food with t h e i r eyes as i t d r i f t e d to the bottom of the tank. The r o l e of the chemical senses i n obtaining food was more d i f f i c u l t to determine. Indiv iduals of both species were ob-served to turn around and swim towards food that had been i n -troduced out of l i n e of the ir s ight some distance away i n a tank. But whether t h i s was a response to chemical s t i m u l i , or to the a c t i v i t y of other f i s h i n the tank, or a chance sight of the experimenter, could not be determined. 3ft B. Method Pre l iminary tests were conducted In an attempt to ascer-t a i n the r o l e that the chemical senses played i n detect ing the presence of food. The tes ts were conducted i n a Y shaped maze ( 2 9 " x 5 i " x 6 i " ) ( F i g . ft). The stem of the Y was par t i t i oned of f with a piece of black p lex ig las ' ( 4 " x 6" x 1/10") which could be ra i sed or lowered on a s t r i n g by the experimenter. The maze was completely enclosed by black polyethylene cur-ta ins with narrow s l i t s through which the f i s h could be ob-served. A continuous flow of dechlorinated water was provided by small ( l / l 6 " ) p l a s t i c hoses dra in ing from two 5 gal lon tanks on a shel f behind the enclosure. These hoses fed in to the two arms of the Y and a siphon drained of f the excess water at the stem of the Y. Water flow through the tubes was contro l l ed by stopcocks. A s ingle f i s h that had been food deprived for about a week was placed i n the stem of the Y behind the p l ex ig la s b a r r i e r i n the evening and l e f t undisturbed overnight. The fol lowing morning approximately 5 ™l of thawed brineshrimp was introduced into one arm of the Y. The b a r r i e r was then ra i sed and the f i s h ' s movements recorded for 30 minutes. Five f i s h of each species were tested i n t h i s way. The d i r e c t i o n and rate of d i f f u s i o n of f l u i d s i n th i s maze were studied by observing the pattern of d i f fus ion of var ious amounts of a 1% so lut ion of methylene blue . It was found that the f i r s t traces of the dye were detectable by the human eye 35 Figure 4. The Y trough used for food detect ion experiments. — p l a s t i c h o s e b l a c k p o l y e t h y l e n e c u r t a i n s s t o p c o c k -90 p l e x i g l a s b a r r i e r - si H P o v e r f l o w p i p e 36 at the stem of the Y a maximum of f ive minutes af ter the dye had been introduced to the arms of the Y. The maximum time for the d i f f u s i o n of the heaviest concentration of the dye i n t h i s manner was f i f t e e n minutes. C . Results The r e s u l t s of t h i s experiment can only serve as an i n d i c a -t i o n of the d i r e c t i o n that future experiments should take, as the number of f i s h tested v/as l i m i t e d by the time ava i lab le for t h i s study. Four out of f ive C. a l eut icus made "incorrect" f i r s t choices (Table X I ) . Only three C. asper made a choice, but a l l three chose c o r r e c t l y . This may be explained i n part by certa in di f ferences i n the behaviour of these species. When C. asper. are disturbed they most often react by: l y i n g very s t i l l for some time a f ter the stimulus i s removed. C. a l eut i cus usual ly swim quickly away from the source of the disturbance (Appendix C). As a r e s u l t , v/hen the b a r r i e r was r a i s e d , the C. asper stayed i n the stem of the Y for as long as 27 minutes before making t h e i r f i r s t choice (Table X I ) . Four out of f ive of the C. a l eu t i cus , however, v/hen disturbed by the b a r r i e r l e f t the stem of the Y i n the f i r s t t h i r t y seconds af ter the b a r r i e r was r a i s e d . The three f i s h that swam into the incorrec t arm moved to the correct a f ter 6 to 6.5 minutes had elapsed. 37 TABLE XI A b i l i t y to detect food by chemical senses, ness of f i r s t choice . Correct -Time of F i r s t Choice (Minutes) Correctness of F i r s t Choice Time of F i r s t Correct Choice (Minutes) C.•asper 1 2 3 k 5 11.5 27 .0 19.5 correct correct correct 11.5 27 .0 19.5 C. a l eu t i cus 1 2 3 k 5 0.5 0 .5 0 . 5 0 . 5 2 0 . 0 incorrec t i n c o r r e c t correct i n c o r r e c t incorrec t 6.0 6.5 0 . 5 6.5 2 3 . 0 38 DISCUSSION Discuss ion of Results Since C. a leut i cus on a sand substrate adopted a f l a t - l y i n g posture (pectoral, f in s fo lded , dorsal f ins extended, body h o r i -zontal) that v/as common i n C. asper i t i s probable that t h i s p o s i t i o n i s a response to C. asper's usual substrate . That t h i s i s indeed a react ion to a sand substrate i s ind icated by the fact that both species exhibited t h i s posture on sand i n current and "noncurrent" condi t ions . Smyley (1957) reported that C. gobio, which inhabi t s areas of slov/ to moderate current , and which exh ib i t s many behavioural t r a i t s s imi lar to those of C. asper, has a marked "preference" for keeping the body i n contact with some surface. The preference on the part of C. a leut icus for the exten-sion of the pectoral f in s on a gravel substrate v/as more marked i n condit ions of "noncurrent" than current . It may be that th i s p o s i t i o n exposes the animal to a cer ta in amount of current , but that the stance has a function that i s s u f f i c i e n t l y "important" to ensure that t h i s posture w i l l be retained i n swift water, a l -though at a reduced frequency. The s igni f icance of th i s ra i sed posture might be that i t permits the animal to catch food d r i f t -ing i n the water or to move with greater ease from stone to stone as i t forages among the rocks. It would also allow the f i s h to maintain a more vi l^gant watch on i t s surroundings. In areas of extreme turbulence and current of greater than 25 cm/sec C. a leut icus put the head down into the current . 39 However t h i s posture was uncommon i n a regu lar , even current except when i t was used for hunting for food. It might enable the animal to maintain pos i t ion i n areas of great turbulence. The funct ional s ign i f i cance of the alignment with respect to the current i s a matter for speculat ion, but i t does appear to be re lated to the postures that the species assume. Animals which l i v e i n a strong current have spec ia l problems which they can meet i n a var ie ty of ways. Animals with streamlined body shapes that o f fer a minimum of res is tance to the water can swim against the current . Those with f lat tened body shapes and c l i n g i n g habits minimize the e f fect of the current by pressing against the substrate . And s t i l l others escape altogether and take shel ter under rocks or i n mats of aquatic vegetation (Needham e t . a l . , 1935). I t could be that facing p a r a l l e l to the current and spreading the pectoral- f ins enables C. a l eut i cus to r e s i s t the current more e f f e c t i v e l y . However, C. asper pre-sumably obtains an even greater degree of securi ty by l y i n g -down between the stones of a gravel substrate . The advantages to C. a l eu t i cus remaining on the surface of the stones must outweigh the increased exposure to the current . The "into" pos i t i on appears to have a spec ia l s igni f icance for C. a l eu t i cu s . Since C. a leut i cus feeds p a r t l y on organisms f l o a t i n g i n the water, the "into" pos i t ion would enable them to detect food f l o a t i n g downstream and to in tercept i t more e f f i c i e n t l y . I f the f i s h faces away from the oncoming current i t has to swim downstream after the food. I f i t faces in to the current i t can dart up to intercept i t . Such quick darts and 40 leaps are more c h a r a c t e r i s t i c of these species than prolonged swimming. The fact that both species assumed the broadside pos i t i on more frequently on sand than on gravel suggests that t h i s p o s i -t i o n i s an adaptation to a sand environment. I t would seem u n l i k e l y that i t has a function as a means of avoiding the cur-rent since i t places more of the f i s h ' s body d i r e c t l y i n the path of the current than any other p o s i t i o n . However, C. asper employed t h i s pos i t i on more frequently i n current than non-current , on sand. Since C. asper i s a poor swimmer, e spec ia l ly i n a current , the s ign i f i cance of t h i s pos i t ion might be that i t enables the animal to move most of the time at an angle to the d i r e c t i o n of flow, so that i t i s l e s s eas i l y displaced by the current . In the l i g h t of the i r feeding behaviour observed i n the laboratory i t i s l i k e l y that C. a leut icus depends oh v i s i o n to a greater extent than C. asper does. C. asper probably depend mostly on t h e i r chemical senses to detect food and only use t h e i r v i s i o n to locate food more prec i se ly as they dart forward to seize i t . The ease and frequency with v/hich C. a l eut i cus take f l o a t i n g food ind ica te that they depend on v i s i o n to some degree. That at l eas t some species of c o t t i d s r e l y on v i s i o n to some extent i s ind ica ted by Smyley (1957) and P h i l l i p s and C l a i r e (1966), who studied C. gobio and C. perplexus respec-t i v e l y , and who found that these species preferred moving food. C. asper's reluctance to feed during the day i s probably 41 re la ted to i t s i n h i b i t i o n against l eav ing the hide during t h i s p e r i o d . Smyley (1957) noted that C. gobio ate very close to the hide and seldom emerged to hunt food, except at n ight . The d i f ference i n swimming a b i l i t y between these species i s probably also re la ted to the i r feeding behaviour, as C. asper appears to be a l u r k i n g predator, at l eas t i n the daytime, whereas C. a leut icus i s an act ive forager and hunter. General Discussion Taylor ( 1966) attempted to determine the extent to which C. asper and C. a l eut i cus select the current and substrate types with which they are associated i n the L i t t l e Campbell R iver . He presented i n d i v i d u a l s of three s ize groups ( less than 40 mm, 40 to 85 mm and 85 to 90 mm) v/ith a choice of f i n e (sand) or coarse (gravel) substrate . He also presented current (45 cm/sec) and "noncurrent" ( less than 7 cm/sec) choices, and current and sub-strate choices simultaneously. His r e s u l t s are summarized on Table XII . Comparing t h i s v/ith the current and substrate con-d i t i o n s at the c o l l e c t i o n s i t e s (Table X I I I ) , one can see that C. a l eu t i cus behaved as one would expect from f i e l d observations. A l l s ize groups selected current and gravel over noncurrent and sand. No s i g n i f i c a n t di f ference v/as detected i n the gravel/sand choice of the larges t s ize group but t h i s accords v/ith the i r occurrence i n the pool habi ta t . S i m i l a r l y , the lack of pre fer -ence with regard to current i n the C. a l eut i cus fry corresponds with t h e i r c o l l e c t i o n i n areas of slow current . The r e s u l t s of the C. asper tests are l e s s convincing i n 42 TABLE XII Summary of r e s u l t s of substrate /current ve loc i ty choice experiments (G. Tay lor , 1966). Condit ion Selected '/Then Presented With: Size Group <40 mm (Fry) C. asper C. a l eu t i cus gravel /sand gravel gravel noncurrent/ current no preference no preference sand/gravel and noncurrent/ current no preference current /grave l 40 to 85 mm C. asner no preference noncurrent C. a l eut i cus gravel current no preference c urrent /grave l 85 to 90 mm C. asper C. a l eut i cus no preference no preference no preference no preference current current /grave l 43 TABLE XIII E c o l o g i c a l data on the areas of the L i t t l e Campbell River from which C. asper and C, a leut icus were c o l l e c t e d . Estuary Lower River Middle River Pools R i f f l e s Most Common Substrate s i l t , mud, oyster s h e l l sand, s i l t , mud sand, f ine gravel coarse and f ine gravel Current* cm/sec 0-30 0-45 <7.5 0-90 Species Col lec ted C. asper C. asper C. asper C . a l e u t i ->100 mm cus C. a leut icus Fry « 4 0 mm) C. a leu-t i c u s >50 mm •measured by Taylor (1966). 4A that a s u r p r i s i n g lack of a preference for noncurrent i s shown.' by two s ize groups. This may have been due to T a y l o r ' s exper i -mental method, v/hich involved checking the f i s h ' s pos i t i on at i n t e r v a l s , rather than continuous observation. He reported that many C. asper never l e f t the s t a r t i n g point where the cur-rent was rather low. Taylor d id f i n d , however, that the greatest divergence i n choice between C. asper and C. a l eut icus occurred i n the s ize group that was most sharply segregated i n nature. T a y l o r ' s laboratory f indings , when compared with h i s f i e l d observations, ind ica te that the laboratory condit ions corresponded to the na-t u r a l hab i ta t . This enables one to assume that behaviour ob-served i n these condit ions i s a r e a l feature of the animal's response to i t s environment. The f indings of t h i s study agree on the whole with T a y l o r ' s . C. asper tends to avoid current on a gravel substrate by l y i n g down among the stones, and to minimize the effect of current on sand by keeping the body pressed f l a t against the substrate . C. a l eut i cus , however, adopts a posture and an or ienta t ion that a c t u a l l y exposes i t to the e f fec ts of the current , on a gravel substrate . That the species are d i f f e r e n t i a l l y adapted to t h e i r mi-crohabitats i n some way i s apparent from T a y l o r ' s r e s u l t s . The f indings of t h i s study ind ica te what some of the behavioural adaptations are . The morphology of C. asper and C. a leut i cus also r e f l e c t s the d i f ferences i n t h e i r habi ta t s . Among re la ted species of 45 f i s h that d i f f e r i n t h e i r swimming habi ts i t i s a general ru le that the more act ive form has a slenderer caudal peduncle and a more streamlined shape than i t s sedentary r e l a t i v e s (Lagler et/ a l . , 1 9 6 2 ) . Dorso-ventral depression i s associated with bottom dwel l ing stream f i s h and i t presumably a ids them i n keeping i n pos i t i on i n a strong current (Lagler et a l . , 1 9 6 2 ) . C. asper i s thus t y p i c a l of the trend i n sedentary bottom dwellers and C. a l eu t i cus i s representat ive of more act ive f i s h . / C . asper and C. a leut i cus lack swim bladders, as do many f i s h which inhabi t swift streams (Lagler et a l . , 1 9 6 2 ) . A l -though the absence of a swim bladder i s no drawback to a seden-tary bottom dweller, i t might at f i r s t appear to be a disadvan-tage to a more act ive species . Swim bladders which function as hydrostat ic organs enable f i s h to expend a minimum amount of energy i n maintaining pos i t i on (Lagler et a l . , 1 9 6 2 ) . However, i n a strong current to be of equal density with the water r e -quires greater, not l e s s , energy to maintain pos i t ion (Lagler et a l . , 1 9 6 2 ) . The mouth s ize of co t t ids i s of the f i r s t importance, as i t determines the s ize of the food that they eat (Northcote, 1 9 5 4 ) . Of the two species considered here, the larger C. asper also has the larger mouth r e l a t i v e to body s i z e . In the labora-tory they feed almost exc lus ive ly on organisms r e s t i n g i n the substrate or f l o a t i n g just above i t . Northcote ( 1 9 5 4 ) reported that C. asper of greater than 5 0 mm mainly eat aquatic insect larvae such as Plecoptera, Ephemoptera, Tr ichoptera , and Diptera (chironomids), which l i v e among weeds and stones'"or burrow i n 46 sand or mud (Macan and Worthington, 1 9 5 1 ) . Sculpin fry eat the l arger planktonic forms, such as Cladocera .and Copepoda (North-cote, 1 9 5 4 ) , -which, l i k e a l l planktonic species, are rather small animals (Macan and. Worthington, 1 9 5 1 ) . A c t i v e , small mouthed scu lp ins , such as C. a l eu t i cus , could continue to ex-p l o i t the plankten as an add i t i ona l food source when adul t s . This would require a superior swimming a b i l i t y and a greater dependence on v i s i o n than the bottom feeding hab i t . I f the f i s h inhabi t s areas of strong current i t must adopt modes of be-haviour that enable i t to obtain t h i s kind of food i n fast wa-t e r . Thus C. a leut i cus or ients p a r a l l e l to the d i r e c t i o n of flow and l i f t s i t s e l f above the rocks on spread pectoral f i n s , permit t ing i t to survey i t ' s surroundings and to launch i t s e l f quickly upwards to catch f l o a t i n g food. C. asper i s a poor swimmer. Such a loss of swimming a f f i -ciency as a r e s u l t of dorso-ventral depression i s , however, of fset by c e r t a i n advantages. These include a gain i n mimetic resemblance to the substrate (Appendix D), and i n the e f f i c i ency of such secret ive habits as the use of stones or other objects as she l ter (Lagler et a l . , 1962),; C. asper i s extremely secre-t i v e , spending most of the brightest hours of the day under logs or stones or i n mats of vegetat ion. SUMMARY This study i s an examination of the behaviour of two r e -la t ed sympatric species which occupy d i f f erent microhabitats to determine which are some of the important behavioural adap-ta t ions to these d i f ferences i n environment. C. asper i s co l l ec ted i n areas of slow current and f i n e l y textured substrate . C. a l eut i cus i s most frequently found i n areas of moderate to fast current and coarse substrate . When exposed to a current i n the laboratory C. asper presses the body against the substrate and l i e s at r i g h t angles to the current , thus avoiding the current , or at l eas t min i -mizing i t s e f fec t s . In a current C. a l eut i cus faces p a r a l l e l to the d i r e c t i o n of flow and on a gravel substrate r a i s e s the body by the expan-sion of the pectora l f i n s . One of the functions of t h i s posture may be that i t enables the animal to s ight on and catch f l o a t i n g food. The spread pectora l f ins might also enable the animal to r e s i s t the current . In both species stance and or ienta t ion to the current seem to be i n part a response to the nature of the. substrate . Both C. asper and C. a l eu t i cus adopt a t y p i c a l l y C. asper posture and or ienta t ion on sand with a greater frequency than on gravel , and C. a l eut i cus type behaviour i s more frequent i n both species on gravel than on sand. However, C. asper s t i l l assumes the broad-side pos i t i on on gravel with an equal or greater frequency than the p a r a l l e l , and C_. a l eut i cus s t i l l shows a preference, 48 although a reduced one, for the p a r a l l e l alignment on sand. Both species appear to employ v i s i o n and the chemical senses i n obta ining food, but to d i f f erent extents. C. a l eu-t i c u s appears to employ v i s i o n more than C. asper does. How-ever, C. asper would require some a id from v i s i o n to sight on the food before dar t ing forward to seize i t . C. a l eut i cus r e l i e s on v i s i o n to locate i t s food when i t feeds on f l o a t i n g organisms. However, the foraging behaviour shown by t h i s species suggests that they also use the chemical senses i n hunting, although perhaps the ir a b i l i t y to detect food i n t h i s manner operates over a much shorter distance than i n C. asper. C. asper i s a very poor swimmer compared to C. a l eut i cus and moves around much l e s s i n both current and noncurrent condi-t i o n s . This corresponds with C. a sper 1 s reluctance to leave i t s hide during the daytime. 49 BIBLIOGRAPHY Bai l ey , Jack E . 1952C L i f e h i s tory and ecology of the sculpin Cottus b a i r d i / p u n c t u l a t u s - i n southwestern Montana. Copeia Bond, C . E . / 1 9 6 3 / D i s t r i b u t i o n and ecology of freshwater sculplns'^genus Cottus, i n Oregon. Ph.D. thes i s . Univer-s i t y of~MichiganT 186 p. Byrne, John E . 1968. The ef fects of photoperiod and tempera-ture on the d a i l y pattern of locomotion a c t i v i t y i n j u -veni le sockeye salmon (Oncorhynchus nerka, Walbaum). Ph.D. thes i s . Univers i ty of B r i t i s h Columbia. 120 p. C a r l , G. C l i f f o r d , W.A. Clemens and C C . L i n d s a y / 1959. The freshwater f ishes of B r i t i s h Columbia, B r i t i s h Columbia p r o v i n c i a l museum Handbook no. 5* 189 p. Daiber, F r a n k l i n C. 1956. A comparative ana lys i s of the winter feeding habits of tv/o benthic stream f i shes . Copeia 1956 Davis, Gerald E . and Charles E . Warren. 1965. Trophic r e l a -t ions of a sculpin i n laboratory stream communities. J . of W i l d l i f e Management 29 ( 4 ) : 846-871. Dineen, Clarence F . 1951- A comparative study of the food ha-b i t s of Cottus b a i r d i i and associated species of s a l -monidae. Am. Midland Natura l i s t 46: 640-645. Dobzhansky, Th. 1956. What i s an adaptive t r a i t ? Am. Natur-a l i s t 90: 337-347. Greenbank, John. 1957. Aggregational behaviour i n a fresh-water s c u l p i n . Copeia 1957 ( 2 ) : 157. Hartley , P . H . T . 1948. Food and feeding re la t ionsh ips i n a community of freshwater f i shes . J . Animal E c o l . 17:1-14. Heard, Wil l iam R. 1965. Limnetic co t t id larvae and the ir u t i l i z a t i o n as food by juveni le sockeye salmon. Trans. Am. F i s h e r i e s . Soc. 94: 191-193. Hinde, R .A . 1959* Behaviour and speciat ion i n b irds and lower vertebrates . B i o l . Rev. 34: 85-128. Kresja , Richard Joseph. 1965. The systematics of the p r i c k l y sculp in Cottus asper:- an inves t iga t ion of genetic and nongenetic v a r i a t i o n within a polytypic species . Ph.D. thes i s . Univers i ty of B r i t i s h Columbia. 183 p. 1952 ( 4 ) : 243-255. ( 3 ) : 141-151. 50 Lack, David. 1 9 6 5 . Evolut ionary ecology. J . Animal E c o l . L a g l e r ^ K a r l F . , John E . BaTd'acM and Robert R. M i l l e r . 1 9 6 2 . ,s\ / Icthyology. John Wiley' and Sons, I n c . , New York. 545 p. L i l e y , N.R. 1966. E tho log i ca l i s o l a t i n g mechanisms i n four sympatric species of p o e c i l i i d f i shes . Behaviour Supple-ment X I I I . 197 p. Macan, T . T . and E . B . Worthington. 1951. L i f e i n Lakes and Rivers . C o l l i n s . London. 272 p. Mason, Herbert L . and Jean H.'Lagenh'eim. 1961. Natural se lec-t i o n as an eco log ica l concept. Ecology 42 (1): 158-165. Mayr, Erns t . 1 9 4 7 . E c o l o g i c a l factors i n spec ia t ion . Evo lu-t i o n 1 ( 3 ) : 263-288. McLarney, Wil l iam 0 . 1 9 6 4 . The coast range sculp in Cottus a l eut i cus : Structure of a population and predation on eggs of the pink salmon, Oncorhynchus gorbuscha. M.S. thes i s . Univers i ty of Michigan. 83 p. M i l l e r , Alden H. 1942. Habitat se lec t ion among higher verte-brates and i t s r e l a t i o n to i n t r a s p e c i f i c v a r i a t i o n . Am. N a t u r a l i s t 7 6 : 25-35. Morr i s , Desmond. 1954. Reproductive behaviour of the r i v e r Bullhead (Cottus gobioj with spec ia l reference to fanning a c t i v i t y . Behaviour 7 (1): 1-32. Needham, James G . , Jay R. Traver and Y i n - C h i Hsu. 1935. The biology of Mayf l i es . Comstock Publ i sh ing Co. I n c . , Ithaca, N.Y. Northcote, Thomas G. 1954. Observations on the comparative ecology of two species of f i s h , Cottus asper and Cottus  rhotheus, i n B r i t i s h Columbia. Copeia 1954 (1): 25-28. , and G . F . Hartman. 1959. A case of "schooling" behaviour i n the p r i c k l y sculp in Cottus asper Richardson. Copeia 1959 (2): 156-158. Orians, Gordon H. 1 9 6 2 . Natural se lec t ion and eco log ica l theory. Am. Natura l i s t 9 6 : 257-263. P h i l l i p s , Robert W. and E r r o l W. C l a i r e . 1 9 6 6 . Intragravel movement of the r e t i c u l a t e s cu lp in , Cottus perplexus, and i t s potent ia l as a predator on salmonid embryos. Trans. Am. F i sher i e s Soc. 95 (2): 210-212. 3 4 : 2 2 3 - 2 3 1 . 51 Roe, Anne and George Gaylord Simpson (eds . ) . 1958. Behaviour and evo lut ion . Yale Univers i ty Press . New Haven, Conn. 555 P. S iege l , Sidney. 1 9 5 6 . Nonparametric s t a t i s t i c s . McGraw-Hill Book Co. Inc. Toronto. 312 p. Simon, James R. and Robert C. Brown. 1 9 4 3 . Observations on the spawning of the scu lp in Cottus semiscaber. Copeia 1943 ( 1 ) : 41-42. Smyley, W . J . P . 1 9 5 7 . The l i f e h i s tory of the Bullhead or M i l l e r ' s thumb (Cottus gobio L . ) . Proc . Z o o l . Soc. London. 128 (2): 4 3 1 - 4 5 3 . Stee l , Robert G.D. and James H. T o r r i e . I 9 6 0 . P r i n c i p l e s and procedures of s t a t i s t i c s . McGraw-Hill Book Co. Inc. Toronto. 481 p. Straskaba, M i l a r , J i r i Chiar , Stanis lav Frank and Vaclav Hruska. 1 9 6 6 . Contr ibut ion to the problem of food compe-t i t i o n among the s cu lp in , minnow and brown t rout . J . Animal E c o l . 3 5 : 3 0 3 - 3 1 1 . Tay lor , Gerald D. 1 9 6 6 . D i s t r i b u t i o n and habitat response of the coastrange scu lp in (Cottus a leut icus) and p r i c k l y scu lp in (Cottus asper) i n the L i t t l e Campbell R iver , B r i -t i s h Columbia. M.Sc. thes i s . Univers i ty of B r i t i s h Columbia. 89 p. Tax, Sol ( ed . ) . i 9 6 0 . Evolut ion af ter Darwin. V o l . I . Uni -v e r s i t y of Chicago Press . 629 p. Thorpe, W.H. 1945* The evolutionary s ign i f i cance of habitat s e l ec t ion . J . Animal E c o l . 14 ( 2 ) : 6 7 - 7 0 . Zarbock, Wil l iam M. 1 9 5 1 . L i f e h i s tory of the Utah scu lp in , Cottus b a i r d i semiscaber (Cope), i n Logan River , Utah. Trans. Am. F i s h e r i e s Soc. 8l ' : 2 4 9 - 2 5 9 . 5 2 A P P E N D I X In the course of t h i s study, many hours v/ere spent simply observing the f i s h i n a var ie ty of s i t u a t i o n s , i n an attempt to form a general impression of t h e i r behaviour. Many inc idents were observed which were not further examined by experiments, but which have considerable bearing on t h i s study. This Appendix, therefore, i s an out l ine of some of the more pertinent of these observations, which make up the background for much of t h i s research. A. Adaptab i l i t y to Laboratory Conditions " C» a l eut i cus appeared toadapt more quickly to the labora-tory condit ions than C. asper. C. a l eut i cus began to eat much sooner af ter they were brought in to the laboratory . In inducing f i s h from the f i e l d to eat, i t was noted that the smaller i n d i -v idua l s of both species were the f i r s t to take the food. By p l a c i n g i n d i v i d u a l s from a group of f i s h that were eating well i n a group that were not eating, i t was poss ib le to induce the second group to eat. Ind iv idua l s of both species were kept a l i v e and i n apparent good health for over a year, i n d i c a t i n g that they were well adapted to laboratory condi t ions . B. Influence on Numbers on Behaviour In keeping these f i s h and i n observing t h e i r behaviour, the numbers of i n d i v i d u a l s kept i n a s ingle tank seemed to be of 53 some importance. Both species exhibited very l i t t l e aggressive behaviour among themselves, except v/hen extremely crowded. A l -though c o t t i d s are t e r r i t o r i a l i n the breeding season (Morris , 1954; Smyley, 1957) and the l arger specimens (greater than 80 mm) were usual ly co l l ec ted only a few at a t ime, there did not appear to be any necessity to separate the f i s h i n i n d i v i d u a l aquaria . In fac t , i t v/as found that whenever the f i s h were i s o l a t e d i n th i s manner they stopped eating and soon d ied . This i s not to say that the deaths were a t t r i b u t a b l e to s tarvat ion , as i n most cases the dead f i s h v/ere of normal weight. V/hen ten to t h i r t y f i s h were kept together, many i n d i v i d u a l s would associate under a s ingle flowerpot. This was p a r t i c u l a r l y marked i n C. asper, which spent so much of t h e i r time i n these refuges. One male C. a l eu t i cus i n breeding 1 condit ion establ ished a t e r r i t o r y i n one flowerpot i n a tank v/ith about f i f t een other f i s h , but very l i t t l e response to h i s d i sp lays was noted i n the other i n d i v i d u a l s . Some aggressive behaviour was seen i n connection with feed-ing when the animals were very crowded. This was p a r t i c u l a r l y not iceable i n C. a l eut i cus , which i n these condit ions custo-mari ly fed with i t s p e c t o r a l , caudal , and dorsal f in s , and sometimes i t s ' operculum spread. This i s very s imi lar to the aggressive behaviour noted by Morris (1955) i n C. gobio. Nor-mally these "displays" d id not r e s u l t i n any overt aggressive a c t i v i t y , although a few inc idents were noted. The most common a c t i v i t y of t h i s nature was pectora l f i n b i t i n g , although there 54 was also some chasing and n ipping . Displays of t h i s nature were also noted i n C. asper, but l e s s frequently, and overt aggressive behaviour was very r a r e . Cases of aggregation behaviour have been reported i n the f i e l d for both C. a l eut i cus (Greenbank, 1957) and C. asper (Northcote and Hartman, 1 9 5 9 ) . C. Response to Unfamil iar St imul i On many d i f f eren t occasions these f i s h were observed when they were presented with unfami l iar objects or s t i m u l i . Some-times t h i s was done d e l i b e r a t e l y , at others i t occurred as a r e s u l t of an experiment that was p r i m a r i l y designed for some other purpose. V/hen the stimulus was an unfamil iar var iant of one which was common i n the natura l environment, such as frozen br ine -shrimp, the f i s h did not behave i n an-."excited" manner. They might ignore the unfamil iar object for minutes or even days; then approach slowly, and f i n a l l y exhibited no avoidance'be-haviour when another such object v/as introduced. St imul i which the human observer might expect to be f r i -ghtening were reacted to i n a var ie ty of ways. An object , such as a styrofoam shape, dragged over the surface i n rather deep water, e l i c i t e d very l i t t l e response other than upward e y e r o l l i n g . However, i f a handnet was dragged along the bottom o f the tank both species became very "excited," swimming quickly away from the disturbed are of the substrate . L ight s of even very low i n t e n s i t y shone on a darkened tank, 55 and tapping on the side of the tank, e l i c i t e d somewhat d i f -ferent behaviour i n the two species . The animal would e i ther "freeze" i n pos i t i on and remain immobile, or i t would swim quickly away, often to the nearest hide. The former react ion was most common i n C. asper, the l a t t e r i n C. a l eu t i cus . D. Crypt ic Colourat ion Both C . asper and C. a leut i cus have a remarkable a b i l i t y t a l t e r the shade and pattern of t h e i r co lourat ion to su i t t h e i r background. This makes them very d i f f i c u l t to see, when they are observed from above. On a uniform, pale coloured background, such as grayish sand, 0 . asper became uniformly pale gray, and the i r f in s are nearly transparent. On a more varied background, such as gray and black gravel and/or brown sand with weeds, they are marbled v/ith f ive or s ix pronounced dark v e r t i c a l saddles under the dorsal f i n s . The b e l l y i s l i g h t coloured. In C. a l eu t i cus , co lourat ion i s f a i r l y c h a r a c t e r i s t i c of the i n d i v i d u a l animal. Most i n d i v i d u a l s are speckled gray and white, with three black saddle marks and black bars on d o r s a l , pectora l and caudal f i n s . A few f i s h , however, are speckled brown and white, producing a sandy colour, with very dark brown or black saddles. In a l l i n d i v i d u a l s on a highly var iable sub-s trate , such as gravel , the saddles are. prominent, but they fad when the f i s h i s placed on a uniform background. 

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