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Effect of a parasitic nematode, Truttaedacnitis truttae on growth and swimming ability of rainbow trout Russell, L. Robert 1977

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EFFECT OF A PARASITIC NEMATODE, TRUTTAEDACNITIS TRUTTAE ON GROWTH AND SWIMMING ABILITIES OF RAINBOW TROUT by L. ROBERT RUSSELL B.Sc, U n i v e r s i t y of B r i t i s h Columbia A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Zoology We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1977 ( O L. Robert Russell, 1977 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced deg ree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t ha t t he L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Depar tment o r 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 o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l 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 . Depa r tment The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook Place Vancouver, Canada V6T 1W5 i i ABSTRACT Growth e f f i c i e n c i e s and swimming a b i l i t i e s of f i n g e r l i n g and l!g year old rainbow trout i n f e c t e d with the nematode parasite T r u t t a e d a c n i t i s truttae are examined. Control trout and trout i n f e c t e d i n the laboratory with 5, 10, 20, 40, or 80 worms exhibited s i m i l a r growth c h a r a c t e r i s t i c s within each of four experimental groups fed d i f f e r e n t r a t i o n s of trout chow (1%, 2%, 3%, or 4% of wet body weight fed per day). S l i g h t l y decreasing growth rates were correlated with increasing numbers of nematode par a s i t e s . Differences between growth rates, amounts of food consumed and growth e f f i c i e n c i e s of in f e c t e d and non-infected f i s h were 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 . C r i t i c a l swimming speed, f i x e d v e l o c i t y and burst v e l o c i t y stamina te s t s revealed s i m i -l a r swimming a b i l i t i e s i n both co n t r o l and in f e c t e d trout. Maximum swimming speeds attained and time to fatigue at c r u i s i n g speeds were more c l o s e l y r e l a t e d to f i s h s i z e and rations f i s h were fed than to numbers of worms with which f i s h were infected. Importance to rainbow trout s u r v i v a l of large natural i n f e c t i o n s with T. nruttae i s discussed. TABLE OF CONTENTS TITLE PAGE ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF APPENDICES ACKNOWLEDGEMENTS INTRODUCTION Source of P a r a s i t i c I n f e c t i o n Source of Experimental Hosts MATERIALS AND METHODS 1. I n f e c t i o n Techniques 2. Growth Experiment 3. Stamina Experiments ANALYSIS OF DATA RESULTS 1. Growth Experiment i . Growth Rate vs. Parasite Numbers i i . Food Consumed vs. Parasite Numbers i i i . Growth E f f i c i e n c y vs. Parasite Numbers i v . Growth Rate vs. Ration v. Food Consumed vs. Ration v i . Growth E f f i c i e n c y vs. Ration v i i . Growth E f f i c i e n c y vs. Growth Rate 2. Stamina Experiments i . Body Morphology and Condition Factor i i . C r i t i c a l V e l o c i t y Tests i i i . Fixed V e l o c i t y Tests i v . Burst V e l o c i t y Tests i v Table of Contents (cont'd) Page DISCUSSION 33 1. Growth Experiments 3$ 2. Stamina Experiments j^f Conclusions 59 LITERATURE CITED 62 APPENDIX ^£7 I V TABLE I. TABLE I I . TABLE I I I . TABLE IV. TABLE V. TABLE VI. LIST OF TABLES Variables tested In growth experiment i a. Dry weight determinations for c o n t r o l and i n f e c t e d rainbow trout fed 1%, 2%,' 3% or 4% rations/day. , b. Dry weight determination of trout chow used to feed experimental f i s h F. values (Model I ANOVA where F[4/24 0.05] = 2.8) f o r differ e n c e i n body morphology measurements between c o n t r o l and i n f e c t e d f i n g e r l i n g rainbow trout maintained on 1%, 2%, or 4% rations Mean condition factors of f i n g e r l i n g and lh yyr o l d rainbow trout p r i o r to stamina experiments Gross and net growth e f f i c i e n c y of f i n g e r -l i n g rainbow trout Active and standard metabolic rates and scope for a c t i v i t y of f i n g e r l i n g and lh yr o l d rainbow trout Page 1.0 20 20 31 32 44 58 v i LIST OF FIGURES FIGURE 1. Growth rate, of in f e c t e d and con t r o l f i n g e r -l i n g and 1% yr old rainbow trout maintained on four d i f f e r e n t food rat i o n s FIGURE 2. Growth rate of f i n g e r l i n g and lh yr old rainbow trout i n r e l a t i o n to number of para-s i t e s with which they were in f e c t e d FIGURE 3. Food consumption of f i n g e r l i n g and 1% yr old rainbow trout i n r e l a t i o n to number of para-s i t e s with which they were in f e c t e d FIGURE 4. Growth e f f i c i e n c y of f i n g e r l i n g and 1% yr old rainbow trout i n r e l a t i o n to number of para-s i t e s with which they were infec t e d FIGURE 5. Growth rate of f i n g e r l i n g and lh yr old r a i n -bow t r o u t / i n r e l a t i o n to rations fed FIGURE 6. Food consumption of f i n g e r l i n g and 1% yr old rainbow trout i n r e l a t i o n to rations fed FIGURE 7. Growth e f f i c i e n c y of f i n g e r l i n g and 1% yr old rainbow trout i n r e l a t i o n to rations fed FIGURE 8. Growth e f f i c i e n c y of f i n g e r l i n g and lh yr old rainbow trout i n r e l a t i o n to growth rate FIGURE 9. Length of f i n g e r l i n g and 1%. yr old rainbow trout i n r e l a t i o n to c r i t i c a l v e l o c i t i e s attained FIGURE 10. Time taken by f i n g e r l i n g rainbow trout (fed 2% rations) to fatigue i n fi x e d v e l o c i t y tests FIGURE 11. Time f i n g e r l i n g rainbow trout (fed 1%, 2%, or 4% rations) maintained burst swimming a c t i v i t y FIGURE 12. Geometrical determination of optimum and maintenance rat i o n s for f i n g e r l i n g rainbow trout FIGURE 13. Growth rate of f i n g e r l i n g and 1% yr old rainbow trout i n r e l a t i o n to f i s h weight FIGURE 14. C r i t i c a l v e l o c i t i e s attained by f i n g e r l i n g and lh yr old rainbow trout i n r e l a t i o n to , f i s h weight and length Page 18 21 22 23 25 26 28 29 33 35 37 42 46 50 List of Figures (cont'd) v i i FIGURE 15. FIGURE 16. Composite swimming curve relating steady and burst swimming a b i l i t i e s of fingerling rain-bow trout Temperature-weight responses for active and standard metabolic rates of fingerling and 1% yr old rainbow trout Page 55 57 LIST OF APPENDICES APPENDIX I. Equations for regression l i n e s appearing i n Figures 2, 3, and 4 APPENDIX I I . Equations for regression l i n e s appearing i n Figure 8 APPENDIX I I I . Equations for regression l i n e s appearing i n Figure 11 APPENDIX IV. Mean lengths, weights and c r i t i c a l v e l o c i t i e s of f i s h used i n stamina experiments i x ACKNOWLEDGEMENTS I wish to express my gratitude to Dr. J.R. Adams, my supervisor, for many valuable suggestions and ideas during the study and for h i s assistance i n preparation of the manuscript. Dr. D.R. Jones provided e s s e n t i a l information regarding performance of stamina experiments and as s i s t e d i n e d i t i n g the write-up. Drs. T.H. Carefoot, J.D. McPhail and Mary Jackson read the manuscript and made many valuable suggestions. Technical assistance was provided by Mr. F. Smith and Mr. B. Land. Many suggestions and ideas were made by Mr. J. D'Silva, Mr. M. Kennedy and Dr. H. Ching. Mrs. P. Waldron kin d l y a s s i s t e d by typing the f i n a l manuscript. F i n a l l y , I wish to thank my wife, Marilyn, for her i n s p i r a t i o n , understanding and assistance i n preparation of the manuscript. 1 INTRODUCTION Rainbow trout are among the most important gamefish c u l t i v a t e d i n North America. As such the diseases and parasites with which these f i s h become i n f e c t e d have been the subject of considerable research (Snieszko, 1970). T r u t t a e d a c n i t i s t r u t t a e fl,ane 1916^is a s p i r u r i d nematode para s i t e that attaches to the i n t e s t i n a l epithelium of the p y l o r i c caeca of rainbow trout (Hiscox and Brocksen, 1973). Infected trout inhabit lakes through-out the c e n t r a l i n t e r i o r of B r i t i s h Columbia (Smedley, 1933; Bangham and Adams, 1954) and C a l i f o r n i a (Hiscox and Brocksen, 1973). The parasite's feeding and attachment a c t i v i t i e s cause severe denudation of the columnar epithelium and probably reduce the absorbtive capacity of the p y l o r i c caeca considerably ( R u s s e l l , unpublished data). As many as 360 of these, nematode parasites have been found i n a s i n g l e mature rainbow trout (person-a l observation). T r u t t a e d a c n i t i s truttae may therefore have numerous de-trimental e f f e c t s on the physiology of i t s host and thus may d i r e c t l y i n -fluence the s u r v i v a l or reproductive c a p a b i l i t i e s of rainbow trout i n B r i -t i s h Columbia. A f i s h ' s growth rate and i t s a b i l i t y to swim (necessary to capture food and avoid predators) are two e s s e n t i a l components of i t s s u r v i v a l (Brown, 1957; B r e t t , 1964). Determination of growth c h a r a c t e r i s t i c s and swimming e f f i c i e n c i e s of trout i n f e c t e d with p o t e n t i a l l y harmful parasites such as T\ truttae should therefore y i e l d useful information about the measurable e f f e c t s of t h i s host-parasite a s s o c i a t i o n . Numerous studies i n v e s t i g a t i n g the growth of animals i n f e c t e d with g a s t r o - i n t e s t i n a l parasites have attempted to determine the extent to which parasites e f f e c t the well-being of t h e i r hosts. Studies of common i n f e c t i o n s i n domestic animals with i n t e s t i n a l nematodes include that of Spindler (1947) who found marked growth i n h i b i t i o n i n pigs during the migration of l a r v a l A scaris lumbricoides. Whitlock (1949) observed i n i t i a l rapid growth followed by reduced growth i n lambs infe c t e d with Trichostrongylus  axei. S i m i l a r l y , reduced food intake and growth e f f i c i e n c y are known to occur i n sheep as a r e s u l t of i n f e c t i o n s with Haemonchus contortus, Trichostrongylus c o l u b r i f o r m i s, Cooperia c u r t i c e i , Nematodirus spathiger, Oesophagostomum columbianum and Bunostomum trigonocephalum by (Spedding et a l . , 1958; Gordon, 1950, 1958; Andrews, 1938; Shumard et a l . , 1957, and Soulsby, 1965). E f f e c t s of parasites on the growth c h a r a c t e r i s t i c s of f i s h have been examined l e s s frequently. I n f e c t i o n of the upper i n t e s t i n e with tapeworm larvae (Proteocephalus sp.) was found by Hubbs (1927) to cause retardation i n growth and an i n t e r r u p t i o n i n development of melanophores and f i n rays i n the c y p r i n i d Platygobis g r a c i l i s . S i m i l a r l y , M i l l e r (1945) demonstrated a reduced growth rate i n coregonid fishes harbouring muscle-encysted p l e r o -cercoids of Triaenophorus crassus and retention of l a r v a l characters and loss of weight i n rainbow trout has been a t t r i b u t e d to the presence of: Echinorhynchus tru t t a e ( S t e i n s t r a s s e r , 1936); Cyathocephalus truncatus (Wisniewsky, 1932), and T_. nodulosus (Novikova, 1934). Sockeye salmon smol :s i n f e c t e d with 5 to 10 Eubothrium s a l v e l i n i were 5 mm shorter and 1 g l i g h t e r than non-infected smolts of the same age (Smith and Margolis, 1970). Con-versely, K l e i n e^ t a l . (1969) observed no e f f e c t of s u b s t a n t i a l numbers of Crepidostomum f a r i o n i s on the length, weight or condition f a c t o r of i n f e c t e d rainbow trout. 3 Few i n v e s t i g a t i o n s of the e f f e c t s on growth of gut-inhabiting nematode parasites of f i s h have been undertaken. Reichenbach-Klinke and Elkan (1965) noted that young salmonids i n f e c t e d with C a p i l l a r i a sp. were emaciated and reluctant to feed. Hiscox and Brocksen (1973), studied the growth charac-t e r i s t i c s , over a ten-day period, of rainbow trout maintained i n i n d i v i d u a l aquaria on various r a t i o n s . They suggest that f i s h harbouring moderate num-bers of Tru t t a e d a c n i t i s t r u t t a e grow more slowly and u t i l i z e food l e s s e f f i -c i e n t l y than controls. Determination of the components de f i n i n g swimming a b i l i t y i n salmonid fis h e s has been discussed extensively by Bainbridge (1960), Brett (1964), Fry and Cox (1970), Webb (1971a, b, 1975) and Brett and Glass (1973). Owing to the importance of swimming to the s u r v i v a l of f i s h i t i s s u r p r i s i n g that measurement of stamina has not been incorporated i n t o more studies of host-par a s i t e r e l a t i o n s h i p s . Fox (1965) and Bu t l e r and Millemann (1971) used c r i t i c a l v e l o c i t y and fi x e d v e l o c i t y swimming tes t s (Brett, 1964) to show that trout and salmon i n f e c t e d ( i n the body musculature) with large numbers of trematode metacercariae a t t a i n lower maximum sustained swimming speeds and fatigue f a s t e r i n endurance swimming tests than controls. Sockeye salmon smolts carrying tapeworm burdens of up to 5% of the wet body weight of the f i s h swam only 2/3 as far as non-infected smolts (Smith and Margolis, 1970). K l e i n ej: 'al. (1969), on the other hand, could f i n d no e f f e c t on stamina of rainbow trout harbouring large numbers of i n t e s t i n a l flukes (Crepidostomum f a r i o n i s ) . Since growth studies reveal much information about.harmful consequences of host-parasite associations and since i n v e s t i g a t i o n of swimming a b i l i t i e s of p a r a s i t i z e d f i s h may y i e l d valuable data on s u r v i v a l p o t e n t i a l of infec t e d f i s h , i t i s my i n t e n t i o n to examine the e f f e c t s of the p a r a s i t i c nematode, 4 Tru t t a e d a c n i t i s t r u t t a e , on the growth c h a r a c t e r i s t i c s and swimming a b i l i t i e s of rainbow trout. Documentation of any e f f e c t s detrimental to the successful s u r v i v a l of rainbow trout may provide useful informa-t i o n f o r f i s h e r i e s b i o l o g i s t s concerned with the incidence of p a r a s i t i c i n f e c t i o n i n B r i t i s h Columbia's gamefish populations. Source of Parasitic Infection Naturally infected rainbow trout were collected in July 1976 by electrofishing from Loon Inlet Creek located at the north-east end of Loon Lake, about 40 miles north-east of Cache Creek, B.C. Mature fish were transported to the University of B.C. in a 450 l i t r e stocking tank and maintained i n a 2000 l i t r e holding tank under natural daylight condi-tions in circulating water at 11°C. Upon dissection these fish were found to harbour between 13 and 360 adult and immature nematode parasites, Truttaedacnitis truttae. Source of Experimental Hosts Two hundred and sixty disease-free 8-month old "domestic stock" rain-bow trout fingerlings, averaging 12 cm in length, were obtained from the Provincial Fish Hatchery at Abbotsfcrd, B.C. in July 1976. Ten fish selec-ted at random were examined for the presence of parasites and none were found. The remaining fish were divided into 4 groups of 60 fish each and maintained in circulating water aquaria at 11°C for 1 week prior to a r t i f i -c i a l parasitic infection. MATERIALS AND METHODS 1. Infection Techniques Adult Truttaedacnitis truttae were dissected from the upper intestine and pyloric caeca of freshly k i l l e d Loon Lake rainbow trout with scissors and fine pointed forcepe. A sample of 60 worms (30 male and 30 female) w a s taken for species determination and measurement. Worms for this purpose wore fixed in warm (20°C) 10% formaldehyde, preserved in 10% glycerine in 70% ethanol, stained with 0.0025% Cotton Blue in Lactophenol and examined with 6 a Leitz compound microscope. Worms to be used for infection purposes were placed with eye droppers into a 5% solution of NaHCO^ in Alsever's saline solution at 10°C (Hiscox and Brocksen, 1973) and stored for not more than 3 hours in buffered Alsever's solution (pH 6.1) at 10°C unti l used to infect hatchery-reared fingerlings. Preliminary infection t r i a l s showed that longer storage periods reduced T_. truttae attachment success. Hatchery-reared rainbow trout were ligh t l y anaethesetized in a 1/10,0.00 solution of MS 222 (Sandoz) , blotted dry on moist toweling, measured to the nearest millimeter and weighed to the nearest 0.1 g on a Sartorius Model 2116 electrobalance. Counted lots of adult nematodes were drawn into a 1 cc syringe (B-D Plastipak #5623) along with 0.2 to 0.4 ml Alsever's solu-tion. The worms were introduced into the test fish stomachs using a 5 cm length of polyethylene tubing 1.19 mm in inside diameter (Intra-Medic For-mulation PHF, Clay Adams and Co.) fitt e d to the syringe with a Luer-Lok adaptor following the per os method of Hiscox and Brocksen (1973). Slightly greater numbers of worms were injected than those desired in the fin a l i n -fection to allow for differential attachment success of the worms (Hiscox and Brocksen, 1973). Thus, where a 10 worm infection was desired 12 worms were introduced. In order to check attachment progress and infection success two fish were k i l l e d at 1/2, 1, 2, 4, 8, and 24 hours post infection. Their pyloric caeca were examined for the presence of _T. truttae. Worms were found loose in the stomach and pyloric caeca up to 8 hours post infection but most were firmly attached to the caecal mucosa after 24 hours. Infection success aver-aged about 80% (80% of the injected worms attached to the caeca). This is 7 consistent with the findings of Hiscox and Brocksen (1973). Using the per-os method described above f i n g e r l i n g f i s h were in f e c t e d with 5, 10, or 20 worms each. Three groups of c o n t r o l f i s h were used. Con-t r o l s were sham-infected, subjected only to handling procedures s i m i l a r to those used for i n f e c t e d f i s h or not handled at a l l . Following i n f e c t i o n a l l experimental f i s h were tagged with a numbered f i n g e r l i n g tag; (3 mm cl e a r p l a s t i c disc sewn through the skin j u s t a n t e rior to the dorsal f i n ) the numbers corresponding to the l e v e l of induced i n f e c -t i o n . Most controls and sham controls were also tagged, the number 0 denot-in g a sham co n t r o l and tags without numbers denoting controls. One t h i r d of the controls were not tagged so that the e f f e c t of the tag on controls could be estimated i n terms of r e l a t i v e growth and stamina. In addition to the f i n g e r l i n g s mentioned above a group of s i x t y 1-1/2 yr old hatchery-reared ranbow trout were also i n f e c t e d (10, 20, 40 or 80 worms in j e c t e d per f i s h ) and tagged according to the number of worms i n j e c t e d . This allowed a comparison of growth and stamina between young and maturing trout l i v i n g with a v a r i e t y of worm burdens. Numbers of T T . truttae introduced were intended to approximate natural worm burdens i n s o f a r as numbers removed from fi e l d - c o l l e c t e ' d trout were con-cerned. The exception was the 20 worm i n f e c t i o n administered to f i n g e r l i n g f i s h . This worm load was chosen to represent the maximum a f i n g e r l i n g coulc: support owing to the small s i z e of i t s p y l o r i c caeca. 2. Growth Experiment Two hundred and for t y f i n g e r l i n g s subjected to the handling and i n f e c -t i o n procedures outlined above were divided into four groups of s i x t y f i s h each and maintained i n 4 i d e n t i c a l c i r c u l a t i n g (approx. 1 length/sec.) water 8" tanks each with a volume of 55 1. Water temperatures were the same i n a l l tanks but fluctuated from 11.5° to 10°C during the experiment. A natural daylight-darkness regime was maintained throughout the study with an i l l u m i n a t i o n during the day of 77 lux at the surface of the water pro-vided by florescent l i g h t s suspended 2.3 m above the tanks. Disturbance of the f i s h was kept to a minimum by covering the tanks with translucent f i b e r g l a s s covers which were removed only during feeding. Each tank of f i s h contained 10 f i s h i n f e c t e d with 5 worms each, 10 with 10 worms, 10 with 20 worms plus 30 controls of which ten were tagged sham-infected f i s h , ten were tagged controls and ten were not tagged. Each group of f i s h was maintained on a rationed diet of e i t h e r 1%, 2%, 3% or 4% of wet body weight per day of Growers Crumbles #3 trout chow (Moore-Clark Co., Utah). During the 10 week experiment, food allotments were adjusted weekly for each r a t i o n group according to weight gained by the f i s h . Fish were fed as many times d a i l y as they required to consume t h e i r r a t i o n with-out wasting any food. F i s h were weighed and measured every seven days using the anaesthetic b l o t - d r y i n g technique described f o r the i n i t i a l i n -f e c t i o n . Two controls and two i n f e c t e d f i s h were removed from each tank at the end of the f i r s t , f i f t h and tenth weeks of the experiment for dry weight determination and to insure that the i n f e c t i o n with T. truttae was s t i l l present. One-and-one-half-year-old rainbow were also included i n a growth experiment. Two groups of 30 f i s h each were maintained i n 1 3 0 ' l i t r e c i r c u l a t i n g (about 1 length/sec) water tanks under temperature and l i g h t regimes i d e n t i c a l to those under which the f i n g e r l i n g trout were kept. 9 These f i s h , maintained on 1% and 3% d i e t regimes, were fed as many times d a i l y as they required to consume t h e i r r a t i o n of Clarks 3/32 inch trout p e l l e t s . Each group of 30 f i s h comprised s i x groups of f i v e f i s h each: 10, 20, 40 and 80 worm i n f e c t i o n s plus two groups of co n t r o l s ; f i v e of which were sham-infected, and f i v e which were handled but not in f e c t e d . A l l of these f i s h were tagged according to the numbers of worms with which they had been i n f e c t e d . These f i s h were weighed on an Ohaus Model 700 T r i p l e Beam Balance and measured every seven days over a ten week period using the anaesthetic b l o t - d r y i n g technique described previously. Food allotments were adjusted according to weight gained. For dry weight determinations f i s h and trout p e l l e t s were f i r s t weighed wet on a model DL T2-1 Torsion Balance, dried to constant weight f o r 48 hours at 100°C i n a Despatch drying oven and reweighed on the Torsion balance to the nearest O.Olg. Table I shows the variables tested i n the growth experiment. 3. Stamina Experiments Following completion of the growth experiment, stamina experiments were undertaken i n order to see whether swimming a b i l i t y was affected as a r e s u l t of p a r a s i t i c i n f e c t i o n . P r i o r to swimming t e s t s , measurements of body morphology i n c l u d i n g length, weight, depth, breadth and volume were taken from a l l f i s h used i n the growth experiments described above. S t a e t l e r d i v i d e r s were used fo r length, width and depth measurements while volume was measured by immersing the f i s h i n a known volume of water i n a graduated c y l i n d e r . Dimensions of p a r a s i t i z e d versus c o n t r o l f i s h were compared using a Model I Analysis of Variance to ensure that an a l t e r a t i o n i n body shape TABLE I VARIABLES TESTED IN GROWTH EXPERIMENTS 10 Age of Fish Infection Level 8 months Ration on which Fish were Maintained (% wet body weight per day) and Number of Fish used at each Infection Level — — — _ __. 1 % 2% 3 % Control(tagged) 1 0 1 0 1 0 10 Control(no tag) « • 11 • 1 Sham Control n i t I t Inf. ( 5 worms) • t i i 1 t I I I n f . ( 1 0 worms) • t 11 1 1 I n f . ( 2 0 worms) 11 11 \\ years Control(tagged) Sham Control I n f . ( 1 0 worms) I n f . ( 2 0 worms) I n f . ( 4 0 worms) I n f . ( 8 0 worms) 1% 5 3 % 5 11 due to p a r a s i t i c i n f e c t i o n had not occurred which would a l t e r swimming performance (Bainbridge 1960, 1962; B e l l and Terhune, 1970, Brett 1964, 1965; Brett and Glass 1973; Fry and Cox 1970; Webb 1971 a,b,1975). The closed c i r c u i t stamina chamber used i n a l l swimming perform-ance tests consisted of a 12.7 cm ID p l e x i g l a s s tube 86 cm i n length through which r e f r i g e r a t e d water was r e c i r c u l a t e d by a v a r i a b l e speed pump. Flow rates i n the chamber had been c a l i b r a t e d previously by Jones e_t a l . (1974) with a modified Aqua-Log flowmeter and were re l a t e d to pump rpm. Three 0.3 cm mesh grids at the head of the chamber i n -troduced microturbulence i n the swimming tube creating a f l a t v e l o c i t y p r o f i l e and allowing a maximum flow rate of 100 cm/sec (Jones et a l . , 1974). An e l e c t r i c g r i d (5 v o l t s ; B r e t t , 1964) at the t a i l end of the stamina chamber induced f i s h to swim to exhaustion or to a t t a i n burst v e l o c i t i e s i n experiments described below. Fresh water was added to the system continuously (10 1/min) and p0£ i n the flow chamber was monitored using an oxygen electrode (Radiometer module PHA 930) to ensure an adequate supply of oxygen to the f i s h . A l l experiments were performed at 10°C, the same as that i n the c i r c u l a t i n g water tanks, i . C r i t i c a l V e l o c i t y Tests As a baseline f o r further stamina experiments c r i t i c a l v e l o c i t i e s (maximum sustained swimming speeds) of cont r o l and i n f e c t e d f i s h were determined i n the following manner. Four co n t r o l or four p a r a s i t i z e d f i s h (12-15 cm long) were introduced into the stamina chamber with the water speed adjusted to lOcm/sec and allowed to e q u i l i b r a t e i n the chamber overnight (Brett, 1964). Black p l a s t i c was wrapped around the head end of the tube to give the f i s h a reference point and to prevent 12 visual disturbance. The following morning the velocity in the chamber was increased i n increments every 20 minutes (Jones, 1971) u n t i l the fish fatigued and were exhausted against the electric grid. Speed increments were adjusted so that c r i t i c a l velocities of a l l the fish (removed one at a time as they fatigued) were attained in six increments (Jones et al_. , 1974) . Fatigued fi s h were measured and the number of worms with which they were infected was recorded. C r i t i c a l velocities were determined for fingerlings on 1%, 2% and 4% rations and for 1% year old rainbow on the 1% diet (one fish tested i n the chamber at a time). Eight controls and eight f i s h i n -fected with the largest numbers of parasites were tested for each diet and age group. Since most fish swam for less than 20 minutes at their f i n a l speed increment, c r i t i c a l velocity was determined by interpolation as des-cribed by Brett (1964) and later formulated by Jones et al.(1974). CV. = Vp + [ (Vf - Vp ) x | | ] where Vp = penultimate water velocity (cm/sec) Vf = f i n a l water velocity (cm/sec) tF = time to fatigue at Vf (sec) t l = time between velocity increments i i . Fixed Velocity Tests Once the maximum sustained swimming speeds had been computed, fatigue tests were conducted in which fish were made to swim at 90% of their c r i t i c a l velocity until exhausted. Test procedures were modifications of those described by Brett (1967) and Jones et al_. (1974) , 13 Four f i n g e r l i n g s (2 c o n t r o l , 2 infected) were allowed to e q u i l i b r a t e overnight i n the stamina chamber at a water v e l o c i t y of 10 cm/sec. The following day flow rates were increased i n 4 equal increments, each l a s t i n g 3 minutes, u n t i l the test v e l o c i t y (90% of the c r i t i c a l v e l o c i t y ) was reached. The test v e l o c i t y was maintained f o r 600 minutes or u n t i l a l l the f i s h had been exhausted. F i s h were removed as they fatigued, t h e i r lengths were measured, t h e i r p a r a s i t e load recorded, and the time-to-exhaustion noted. A comparison of fatigue times of control and i n f e c t e d f i s h was made (12 con t r o l and 12 i n f e c t e d f i n g e r l i n g s on 2% rations only were tested) i n order to asce r t a i n any differences i n sustained swimming a b i l i t y as a r e s u l t of p a r a s i t i c i n f e c t i o n , i i i . Burst Swimming Tests For these tests the stamina chamber was modified by p l a c i n g 3 F a i r c h i l d FPT 100 phototransistors 25 or 30 cm from the e l e c t r i c g r i d . Single f i s h were allowed to e q u i l i b r a t e i n the chamber f o r % hour p r i o r to each burst swimming t e s t . F i s h were shielded from outside d i s t u r b -ances by allowing them to rest i n an area blacked out with p l a s t i c f i l m immediately ahead of the deactivated g r i d . In a burst t e s t , the f i s h ( r e s t i n g i t s t a i l against the grid) was subjected to a 100 v o l t shock for 20 milliseconds which frightened i t into burst swimming along the tube. As i t passed through the l i g h t beam between the phototransistors and the l i g h t source (American O p t i c a l Illuminator //735C) a trace on a Tektronix Type 564B storage o s c i l l o s c o p e (triggered v i a a Grass S6C stimulator) was interrupted which registered the time of the burst. Oscilloscope traces were photographed with a Polaroid CR-9 Land Camera 14 using Type 107 film and time elapsed during burst swimming was com-puted from measurement of trace lengths taken from the photographs. Distance the fish travelled multiplied by the time elapsed gave the burst velocities attained. A l l control and infected fingerling trout at a l l ration levels were tested four times each on two occasions in order that maximum swimming speeds of parasitized and control fish could be compared. 15 ANALYSIS OF DATA Growth Experiment Mean growth rates, amounts of food consumed, and growth e f f i c -i e n c i e s of f i s h at each l e v e l of i n f e c t i o n ( c o n t r o l , sham c o n t r o l , no-tag c o n t r o l , 5 worms, 10 worms, 20 worms, 40 worms, or 80 worms per fi s h ) w i t h i n a p a r t i c u l a r r a t i o n group and age category were compared using covariance a n a l y s i s . Regression l i n e s were drawn r e l a t i n g the following components of experimental trout growth: Growth Rate vs Number of Parasites with which Fi s h were Infected Food Consumption vs Number of Parasites with which F i s h were Infected Growth E f f i c i e n c y vs Number of Parasites with which F i s h were Infected Food Consumed vs Ration ( f i n g e r l i n g trout) Growth E f f i c i e n c y vs Growth Rate Si g n i f i c a n c e of regressions obtained was compared (analysis of co-variance) and re l a t e d to numbers of parasites with which f i s h were i n -fected and the rations on which f i s h were maintained. Regression co-e f f i c i e n t s representing i n f e c t e d and non-infected trout were determined for each regression and compared using a t t e s t . Swimming Experiments Data r e l a t i n g length and v e l o c i t y ( c r i t i c a l v e l o c i t y t e s t s , lh y r . old t r o u t ) , time to fatigue and v e l o c i t y ( f i x e d v e l o c i t y tests) and time maintained and v e l o c i t y (burst v e l o c i t y tests) were described by l i n e a r regressions representing swimming a b i l i t i e s of p a r a s i t i z e d and contr o l trout fed various rations of trout chow. Si g n i f i c a n c e of r e -gressions obtained was tested by analysis of covariance. Differences 16 between regression coefficients of infected and non-infected fish on each ration were compared using a t test. Length vs velocity data derived from c r i t i c a l velocity measure-ments of fingerling trout were not suitable for regression analysis. Maximum sustained swimming speeds of control and infected finger-lings tested were therefore compared using a t test. o 17 RESULTS 1. Growth Experiment No significant differences (p = 0.05) between growth rates of control and infected fingerling trout were observed during the ten week period of the study (Fig 1 a-d) although control fish grew slightly faster than infected fish at each ration level. Among para-sitized f i s h , those harbouring more worms grew more slowly than those infected with fewer worms. Fish maintained on 1% wet body weight per day rations grew to about 1/3 the size of fish fed 3% rations. No difference in growth was observed between fis h kept on 3% and 4% rations. Growth rates of control and infected f i s h were similar also i n the groups of \\ year old rainbow maintained on 1% and 3% rations (Fig l e , f ) . As a group, infected f i s h grew slightly faster than controls on 1% rations whereas on 3% rations controls had a slightly greater rate of growth than trout infected with T. truttae. However, no significant difference (p=0.05) in growth between groups of parasi-tized and unparasitized fish was observed. Trout maintained on 3% rations grew about three times as fast as those fed 1% rations. 'Comparison of growth curves of 8 month and \\ year old fi s h (Fig 1) revealed a lower over a l l increase in body weight during the ten week period for lh year old trout. These data confirm the findings of Brown (1957) and Brett and Shelbourn (1975) in which larger fish maintained on diets of the same proportion as smaller fish grew at a slower rate. To analyse more completely the data on relative growth of control 17a Figure 1. Growth rate of infected and control fingerling and 1-ir year old rainbow trout maintained on four different food rations* Vertical bars represent + 2 S.E. IS R O w T 200 R * 160 E . % INC. WET WT 120 80 i 40 1% t MO 3 % 8 MO 2 % 8 MO 4 / o 8 MO M0 G R 0 120 H w A 1 80-°/o INC. 6 0 . WET W T . 40 20 1 2 4 6 8 T I M E ( W E E K S ) 160 140 H 120 ioo H 80 60 40 20H 1 2 P C O N 0 / :INF 1 i YR, 10 TIME ( W E E K S ) INFECTION KEY C C O N T R O L 5 5 WORM INFECTION NT NO TAG CONTROL 10 10 " S S H A M C O N T R O L 20 20 " " 19 and i n f e c t e d f i s h on d i f f e r e n t r a t i o n s , growth e f f i c i e n c i e s (K) were determined from the growth rates ( A w ) and food consumption rates ( R A t) of experimental f i s h using the formula derived by Paloheimo and D i c k i e (1966a,b) where log K = l o g (Aw/RAt) Growth and consumption were expressed as mg/g dry weight of fish/day using conversion factors from dry weight determinations of e x p e r i -mental f i s h and trout chow (Table I I ) . Growth rat e s , consumption rates, and growth e f f i c i e n c i e s were then compared with numbers of parasites with which f i s h were i n f e c t e d and rations which f i s h were fed. The r e l a t i o n s h i p between growth e f f i c i e n c y and growth rate was then determined i n order that a comparison of r e s u l t s of t h i s growth study with previous growth experiments could be made, i , i i , i i i . Growth Rate, Food Consumption, and Growth E f f i c i e n c y vs Numbers of Parasites with which F i s h were Infected Growth rates and amounts of food consumed were compared with para-s i t e load (Fig.2a,b; Fig.3a,b). No s i g n i f i c a n t c o r r e l a t i o n s (p=0.05) were found for e i t h e r f i n g e r l i n g or 1% yr old trout maintained on any r a t i o n . These r e s u l t s suggested that the nematode i n f e c t i o n s used had no apparent e f f e c t on the rate of growth or amount of food consumed by the t e s t f i s h . No s i g n i f i c a n t c o r r e l a t i o n s (p=0.05) between growth e f f i c i e n c y and number of parasites with which f i s h were infected were obtained at any r a t i o n l e v e l with e i t h e r f i n g e r l i n g or 1% yr old f i s h (Fig.4a,b). This indicated that T. truttae had no demonstrable e f f e c t on the TABLE II 20 a. DRY V/EIGHT DETERMINATIONS FOR CONTROL AND INFECTED TROUT FED \%t 2%. 3%. OR k% RATIONS/DAY Diet \% 2% 3% ho/0 Infection Level Inf. Con. Inf. Con. Inf. Con. Inf. Con. % Wet Weight 22.a 23.0 28.9 27.2 28,9 24.8. 25-5 26.3 (mean of 5 determinations) D. DRY WEIGHT DETERMINATION OF TROUT CHOW USED TO FEED EXPERIMENTAL FISH Trout Chow % Wet Weight (mean of 5 determinations) 96.31 20a Figure 2. Growth rate of f i n g e r l i n g and year o ld rainbow trout i n r e l a t i o n to number of parasites with which they were i n f e c t e d . 21a Figure 3. Food consumption of fingerling and year old rainbow trout in relation to number of parasites with which they were infected. 22 160* N U M B E R OF PARASITES RATION • \*yo GROUP O 3°/g 22a Figure if. Growth efficiency of fingerling and 1£ year old rainbow trout in relation to number of parasites with which they were infected. 23 24 conversion e f f i c i e n c y of rainbow trout under the conditions of these growth experiments. Equations f o r regression l i n e s appearing i n Figures 2,3 and 4 are presented i n Appendix I. i v . Growth Rate vs Ration Growth rates of f i n g e r l i n g trout increased r a p i d l y from 1% to 2% rations (7.5- 12 mg/g dry wt/day), whereas from 2% rations up to the maximum 4%, increases i n growth rate were les s pronounced (Fig.5a). Growth rate curves were s i m i l a r for both inf e c t e d and non-infected f i s h . The histogram representing growth of 1% yr old trout (Fig.5b) shows a two to t h r e e - f o l d increase i n growth rate for f i s h fed 3% rations compared with those f i s h fed 1% r a t i o n s . Since 2% and 4% r a t i o n l e v e l s were not incorporated into these experiments owing to space l i m i t a t i o n s , the gradual decline i n the increase i n growth rate with in c r e a s i n g r a t i o n observed for f i n g e r l i n g trout was not seen. Differences between growth rates of control and i n f e c t e d f i s h were 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 (p=0.05) at e i t h e r the 1% or 3% r a t i o n l e v e l . v. Food Consumed vs Ration Correlations between food consumed and rations fed experimental f i s h were s i g n i f i c a n t (p=0,01) and p o s i t i v e for f i n g e r l i n g trout (Fig.6a). There was no s i g n i f i c a n t d i f f e r e n c e (p=0.05) between re -gression c o e f f i c i e n t s f o r the l i n e s representing p a r a s i t i z e d and c o n t r o l f i s h . Food consumed by 1% yr old f i s h i n r e l a t i o n to rations fed i s 24a Figure 5. Growth rate of fingerling and year old rainbow trout i n relation to rations fed (1%, 2%, 3%, or 4% of wet weight of fish fed per day). Vertical bars represent ± 2 S.E. 25a Figure 6. Food consumption of fingerling and 1-jr year old rainbow trout in relation to rations fed (1%, 2%, 3%, or k% of wet weight of fish fed per day). Vertical bars represent + 2 S.E. 27 shown i n F i g . 6b. Infected and non-infected trout ate approximately equal amounts of trout chow at each r a t i o n l e v e l . These data suggest that food was consumed i n d i r e c t proportion to the amount of food fed. v i . Growth E f f i c i e n c y vs Ration Growth e f f i c i e n c i e s of 8 month old f i n g e r l i n g s were greatest at 2% r a t i o n l e v e l s (K=0.185) and decreased by about 1/3 at r a t i o n l e v e l s of 3% and 4% (Fig.7a). E f f i c i e n c y curves were s i m i l a r f o r control and p a r a s i t i z e d f i s h . Since 1% yr old f i s h were maintained on only two r a t i o n l e v e l s , growth e f f i c i e n c y vs r a t i o n was represented by a histogram (Fig.7b). Growth e f f i c i e n c i e s decreased only s l i g h t l y for f i s h fed 3% rations i n r e l a t i o n to e f f i c i e n c i e s of f i s h maintained on 1% r a t i o n s . Control and i n f e c t e d trout showed s i m i l a r growth e f f i c i e n c i e s at each r a t i o n l e v e l ( t t e s t ; p= 0.05). v i i . Growth E f f i c i e n c y vs Growth Rate S i g n i f i c a n t p o s i t i v e c o r r e l a t i o n s (p=0.01) between growth e f f i c i e n c y and growth rate were obtained for both co n t r o l and i n f e c t e d f i s h at a l l r a t i o n l e v e l s and for both f i n g e r l i n g and lh year age classes (Fig.8a and b). No 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 s be-tween the regression c o e f f i c i e n t s of the l i n e s representing co n t r o l and i n f e c t e d f i s h were observed. These r e s u l t s i n d i c a t e that i n c r e a s -i n g growth rates imply increasing growth e f f i c i e n c i e s at a f i x e d r a t i o n l e v e l . In a d d i t i o n , comparison of regression l i n e s for d i f f e r -ent rations i n Figure 8 suggests that f i s h maintained on lower rations u t i l i z e t h e i r food more e f f i c i e n t l y f o r a given rate of growth than do 2J7a Figure 7. Growth efficiency of fingerling and 1-J year old rainbow trout in relation to rations fed (1%, 2%, 3%, or k% of wet weight of fish fed per day)» V e r t i c a l bars represent + 2 S.E. 28a Figure 8 . Growth efficiency of fingerling and l£ year old rainbow trout in relation to growth rate. Percentage figures represent different groups of experimental fish fed different rations of trout chow Z%t 3%, or 4% of wet weight of fi s h fed per day). 2 9 030 CON 8 mo © INF B INF RATION O C O N / ° C O N , GROUP 2 / o * S o A INF • INF A CON V CON 8 10 12 14 16 18 20 22 24 G R O W T H R A T E ( M g / ^ D R Y W T / D A Y ) V o •»/• o R A T I O N ©INF BINF GROUP OCON O C O N ~r 9 i 10 12 G R O W T H R A T E ( M g / g O R Y W T / D A Y ) 30 f i s h fed l a r g e r r a t i o n s . Equations describing these regression l i n e s are presented i n Appendix I I . 2, Stamina Experiments i . Body Morphology and Condition Factors of Experimental F i s h No s i g n i f i c a n t d i f f e r e n c e (p=0.05) i n body shape between con t r o l and i n f e c t e d f i n g e r l i n g s maintained on 1%, 2% or 4% r a t i o n s was ob-tained. (Table I I I ) . Condition factors of p a r a s i t i z e d and c o n t r o l f i s h , , computed using the formula 100 W where W = weight(g) L = length (cm) were s i m i l a r within each r a t i o n group i n both 8 month ( f i n g e r l i n g ) and 1% year age categories (Table IV). These findings allowed swimming performance tests to be undertaken without consideration of the influence of differences i n body morphology or condition factor between in f e c t e d and non-infected trout. i i . C r i t i c a l V e l o c i t y Tests C r i t i c a l v e l o c i t i e s (measured i n Lengths/sec) attained by ex-perimental f i s h are p l o t t e d i n r e l a t i o n to lengths of f i s h tested (Fig.9a-d). Data representing f i n g e r l i n g trout appeared to be clumped due to the r e s t r i c t e d s i z e range of f i s h tested i n each r a t i o n category and was therefore unsuitable for regression a n a l y s i s . T tests were used to compare c r i t i c a l v e l o c i t i e s of control and i n f e c t e d f i n g e r l i n g s i n each r a t i o n group. No 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 -ences (p= 0.05) i n maximum sustained swimming speeds of i n f e c t e d and TABLE I I T F VALUES (MODEL I ANOVA WHERE F( !j 0 . 0 0 5 ) = 2 . 8 ) FOR DIFFERENCES IN BODY MORPHOLOGY MEASUREMENTS BETWEEN CONTROL AND INFECTED FINGERLING RAINBOW TROUT MAINTAINED ON 1%. 2%. OR k% RATIONS D i e t V/L L/B W/L n 0 . 3 3 1 . 1 5 1 . 1 4 0 . 8 Z% 0 . 8 7 2 . 3 1.5 0 . 8 5 k% 1 . 2 9 0.58 0 . 6 7 0 . 8 1 V= Volume (cc) L= L e n g t h (cm) B= Breadth (cm) D= Depth (cm) W= Weight (g) TABLE IV MEAN CONDITION FACTORS OF FINGERLING AND \$ YEAR OLD RAINBOW TROUT PRIOR TO STAMINA EXPERIMENTS Age yr Ration Infection Level Condition Factor n 8 mo 8 ao 8 mo 8 mo 1 % 8 0 worms 1 . 2 5 5 1 1 1 0 » « 1 . 2 0 5 t t 2 0 « • 1.31 4 1 1 40 " 1.31 5 1 1 Sham Control 1 . 2 9 4 1 t Control 1.28 5 y/o 8 0 worms 1 . 4 5 5 1 0 • • 1.28 5 • i 2 0 « ' 1 . 4 5 5 1 1 4 0 •' 1.44 5 • i Sham Control 1 . 4 6 5 1 1 Control 1 . 4 ? 5 1 0/ I /o 5 worms 1 . 1 4 8 1 I 10 ' • 1.71 7 1 1 2 0 1' 1.20 8 1 1 No Tag Control 1 . 1 6 1 0 1 1 Sham. Control 1 . 1 8 6 1 1 Control 1 . 1 8 8 2 % 5 worms 1 .22 6 I t 1 0 • • 1 . 2 4 8 1 f 2 0 • • 1.31 7 1 1 No Tag Control 1 . 2 5 1 0 1 t Sham Control 1 . 2 9 8 1 1 Control 1.26 7 5 worms 1 . 3 6 8 10 •» 1.2 9 7 1 1 2 0 '1 1 . 2 6 6 1 1 No Tag Control 1 . 2 3 8 •» Sham Control 1 . 2 9 7 Control 1.25 7 k% 5 worms 1 . 3 3 8 1 1 10 . • « 1 . 3 6 7 1 1 2 0 »' 1. 3 5 6 • i No Tag Control ' 1.28 7 1 1 Sham Control 1 . 2 7 8 1 1 Control 1.35 8 32a Figure 9 . Length of fingerling and 1-£ year old rainbow trout in relation to c r i t i c a l velocities which they attained. Percentage figures represent different groups of experimental fish fed different rations of trout chow (1%, 2%, or k% of wet weight of fish fed per day) . 34 non-infected fingerling trout were found. Regression analysis of data representing swimming performances of 1% yr old fish fed 1% rations revealed significant (p=0.01) negative correlations between length and c r i t i c a l celocity (Fig.9d). Differences between regression coefficients of infected and non-infected trout were not s t a t i s t i c a l l y significant. These data suggest that in fish populations of uniform size (fingerlings on 1% rations, 12- 15 cm; fingerlings on 2% rations, 14- 16.5 cm; fingerlings on 4% rations, 15- 19 cm) c r i t i c a l veloci-ties which trout may attain may resemble a random distribution. In populations where there i s considerable range in size (lh yr old fish fed 1% rations, size range 22.5- 31.5 cm) larger f i s h attain relatively lower c r i t i c a l velocities than smaller fish. i i i . Fixed Velocity Tests A significant negative correlation (p=0.05) between time to fatigue and velocity was found for fingerling fish on 2% rations swum at 90% of their mean c r i t i c a l velocity (49.76 cm/sec) when the time interval 20 seconds to 200 minutes was plotted (Fig.10). Brett (1964) demonstrated a sustained swimming capacity in fis h which maintained imposed fatigue velocities for longer than 200 minutes. Similarly, when times to fatigue from 200 to 600 minutes vs velocity were plotted for fingerlings on 2% rations (Fig.10) no significant correlation was obtained (p=0.05) indicating continuous performance by the fish s t i l l swimming after 200 minutes. No significant difference (p=0.05) between regression coefficients of infected and control fish was found. iv. Burst Velocity Tests Significant negative correlations between time maintained and 34a Figure 1 0 . Time taken by fingerling rainbow trout (fed 2% rations) to fatigue i n fixed velocity tests. Regressions representing control and infected fish are compared. 0.1-0.05-J 0 VEL0C5IY(L/SEC.) 36 burst v e l o c i t y were obtained for a l l f i n g e r l i n g r a t i o n groups (Fig.11). Control f i s h on 1% r a t i o n s , i n f e c t e d and con t r o l f i s h on 3% rations and in f e c t e d f i s h on 4% rations were represented by cor-r e l a t i o n s s i g n i f i c a n t at the p=0.01 l e v e l . Infected f i s h on 1% rations and control f i s h on 4% rations showed co r r e l a t i o n s between time main-tained and burst v e l o c i t y s i g n i f i c a n t at the p=0.05 l e v e l . No s i g n i f i -cant diff e r e n c e (p=0.05) between regression c o e f f i c i e n t s of infec t e d and control trout was found. These r e s u l t s suggest that as burst v e l o c i t i e s increase the time f o r which they can be maintained decreases. Equations f o r regression l i n e s appearing i n Figure 11 are pre-sented i n Appendix I I I . 36a Figure 11. Time fingerling rainbow trout (fed 1%, 2%, or W/o rations) maintained burst swimming activity. Regressions representing control and infected fish are compared. VELOCITY (L SEC.) 33 DISCUSSION The growth c h a r a c t e r i s t i c s and swimming a b i l i t i e s of f i s h are two components of t h e i r physiology e s s e n t i a l to s u r v i v a l . I t was the purpose of t h i s i n v e s t i g a t i o n to determine the e f f e c t of T r u t t a e d a c n i t i s  t r u t t a e , a p a r a s i t i c nematode, on these components i n rainbow trout. The following discussion examines growth parameters (growth rates, food consumption and growth e f f i c i e n c i e s ) and stamina measurements ( c r i t i c a l v e l o c i t i e s , time to fatigue at f i x e d v e l o c i t i e s and burst v e l o c i t i e s of p a r a s i t i z e d and c o n t r o l trout maintained on four d i f f e r e n t rations i n r e -l a t i o n to the i n t e r p r e t a t i o n s of other experiments reported i n the l i t e r -ature. In addition, suggestions for further study of the T_. truttae -Salmo gairdneri host-parasite r e l a t i o n s h i p are presented. 1. Growth Experiment Comparison of growth rates of i n f e c t e d and control trout ( F i g . 1) shows that control f i s h usually grew s l i g h t l y f a s t e r than i n f e c t e d f i s h (growth rates not greater s t a t i s t i c a l l y ) at a l l r a t i o n l e v e l s and that those f i s h with the greatest number of nematodes grew most slowly. Fur-ther examination of the data i n terms of amount of food consumed and rate of growth per gram dry weight of f i s h tissue per day compared with numbers of p a r a s i t e s with which f i s h were i n f e c t e d (Fig. 2 and 3) reveals s l i g h t l y decreasing growth rates and no appreciable difference i n food consumption with increasing numbers of parasites at any given r a t i o n l e v e l . Similar gradually decreasing growth rates as a function of numbers of T_. truttae have been found by Hiscox and Brocksen (1973). Whereas these authors 39 noted increasing consumption rates i n r e l a t i o n to degree of i n f e c t i o n (parasite numbers), my data suggest increasing food intake only at the highest (4%) and lowest (1%) r a t i o n l e v e l s ; amount of food consumed de-creased i n r e l a t i o n to numbers of parasites at r a t i o n l e v e l s of 2% and 3%. These differences may be explained by the fa c t that Hiscox and Brocksen examined consumption by measuring the amount of food consumed by i n d i v i d u a l f i s h whereas my experimental design assumed that each f i s h within a r a t i o n group ( s i x t y f i s h per group) consumed i t s a l l o t t e d r a t i o n per day and therefore amount of food consumed was dependent on the weight of the f i s h and i t s i n d i v i d u a l rate of growth. Thus, a decrease i n the amount of food consumed by f i s h on 2% and 3% rations with an increase i n the numbers of parasites suggests that growth rates of i n f e c t e d f i s h on these r a t i o n s decrease to a s l i g h t l y greater degree as a function of numbers of worms than do growth rates of i n f e c t e d f i s h on 1% or 4% r a -t i o n s . Nevertheless, differences i n growth rates and food consumption between in f e c t e d and c o n t r o l f i s h were 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 at any r a t i o n l e v e l . Comparison of growth e f f i c i e n c y with numbers of parasites (Fig. 4) suggests that food consumed by controls was more e f f i c i e n t l y converted to f i s h tissue than food eaten by i n f e c t e d f i s h . These r e s u l t s i n general confirm the findings of Hiscox and Brocksen (1973) although t h e i r values for growth e f f i c i e n c y are as much as twice as large as those found i n this study. As the f i s h i n this experiment were not i n d i v i -d ually fed, wastage of food, p a r t i c u l a r l y at higher r a t i o n l e v e l s , may have resu l t e d i n overestimation of the amount of food consumed and hence 40 would lower calculated growth e f f i c i e n c i e s . In a d d i t i o n , growth ex-periments i n this i n v e s t i g a t i o n were performed during the l a t e summer and e a r l y f a l l and may have coincided with a p h y s i o l o g i c a l cycle inher-ent i n some salmonids which decreases the growth rate and thus, the growth e f f i c i e n c y , at t h i s time of year (Brown, 1957). The present study was performed at 9 to 11°C. Brown (1946a) has suggested that between 9 and 16°C growth e f f i c i e n c y w i l l be lower than at 7-9°C or 16-19°C since maintenance requirements and metabolic rates are highest between 9 and 16°C. In addition, Brown (1946a), and Davis (1934) detected differences i n growth which coincided with genetic s t r a i n s of trout. The trout with which these experiments were performed may have been bred d i f f e r e n t l y than those used by Hiscox and Brocksen (1973) and hence may have been incapable of growing as e f f i c i e n t l y . F i n a l l y , some of the 1% year old f i s h may have been approaching maturity and hence may have been convert-ing considerable amounts of food energy into reproductive products at the expense of f i s h tissue (Aim 1939, 1949; Millenbach, 1950). As a means of comparing the r e s u l t s of t h i s growth study with those of other i n v e s t i g a t i o n s growth rates and growth e f f i c i e n c i e s were com-pared with d i f f e r e n t rations assigned. Figure 5 i l l u s t r a t e s the r e l a t i o n -ship between growth rates of co n t r o l and inf e c t e d f i s h and r a t i o n . While there i s no appreciable difference between the slopes of the curves for con t r o l and i n f e c t e d f i s h (confirmed by Hiscox and Brocksen, 1973) i t i s apparent that increases i n growth rate are greater when 1% to-2% rations are fed than when 2% to 4% rations are administered ( F i g . 5a). These r e -s u l t s are consistent with those of Le Brasseur (1969) and Brett e_t_ a l . (1969) and the i n f l e c t i o n of the curves at 4% rations indicates that the 41 ration i s being approached at which food presented w i l l no longer re-sult i n an increase in growth rate. By plotting growth rate (% i n -crease i n wet wt/day) and ration on axes which allow negative growth rates to be displayed (Figure 12) the maintenance (minimum ration which w i l l allow zero growth) and optimum (ration level at which maximum growth rate occurs) rations may be determined geometrically (Thompson, 1941; Warren and Davis, 1967; Brett et_ al_. , 1969). In this manner the tangent from the origin to the curve determines the optimum ration and the main-tenance ration is determined by the point at which the growth curves intercept the line of zero growth. Using this procedure an estimated ration of 1.5 to 1.6% per day would result in maximum growth rates for fingerling fish (similar values for both control and infected fish). Maintenance rations derived in a similar manner would approximate 0.3% of wet body weight/day. While these estimates are slightly below those of Brown (1946c) and Brett e_t a l . (1969) who used different species of salmonids at different times of the year, they provide additional infor-mation concerning the growth characteristics of the population of fish used in this study. The use of only two ration levels in growth studies with lh year old fish (resulting in a strcug-kt line rather than a curve for growth vs. ration) precludes derivation of maintenance and optimum rations for these animals. Derivation of the maintenance ration allows further calculation of the net growth efficiency (Modified from Brett et_ a l . , 1969) such that Kn = AW/RAt - Rm where Kn = net growth efficiency; AW = growth rate; RAt = total food con-41a Figure 1 2 . Geometrical determination of optimum and maintenance rations for fingerling rainbow trout. Optimum rations determined by a vertical line dropped from the tangent of the growth curves; maintenance ration determined by the point at which the growth curve bisects the line of zero growth. 42 43 sumption and Rm = food required f o r maintenance. Growth e f f i c i e n c y c a l c u l a t i o n s presented previously i n t h i s paper were derivations of gross growth e f f i c i e n c y since values.for maintenance rations were not known. Net e f f i c i e n c y values describe the actual e f f i -ciency of conversion of food i n t o new f i s h t i s s u e a f t e r subtraction of amounts of food required f o r maintenance of e x i s t i n g body tissues has been made (Brett et a l . , 1969). Thus, net growth e f f i c i e n c i e s f o r a given population w i l l be greater than gross growth e f f i c i e n c i e s . Net growth e f f i c i e n c y values obtained for t h i s i n v e s t i g a t i o n (Table V) are greatest f o r f i s h fed 1% rations and l e a s t f o r f i s h maintained on 4% r a -t i o n s . Comparable r e s u l t s have been obtained by Warren and Davis (1967) and Brett et_ al_. (1969) , who found that net growth e f f i c i e n c i e s were greater f o r f i s h fed lower rations than f i s h fed l a r g e r amounts of food. Comparison of gross growth e f f i c i e n c y with r a t i o n (Fig. 7) reveals a decrease i n e f f i c i e n c y (negative K l i n e ) f o r rations over 2% of wet body weight/day for both i n f e c t e d and c o n t r o l f i n g e r l i n g trout and a s t e a d i l y decreasing e f f i c i e n c y f o r lh year old f i s h fed rat i o n s amountin to more than 1% of t h e i r wet body weight/day. Similar decreasing growth e f f i c i e n c i e s have been described by Paloheimo and Dickie (1965, 1966a, 1966b), Warren and Davis (1967), La Brasseur (1969) and Kerr (1971). Growth e f f i c i e n c i e s increase between 1% and 2% r a t i o n l e v e l s f o r f i n g e r -l i n g trout i n t h i s experiment (Fig. 7a). Kerr (1971) has suggested that p o s i t i v e K l i n e s such as these are a r e s u l t of a lower metabolic expendi ture on spontaneous a c t i v i t y than i s provided f or by the r a t i o n fed. r Thus, f i s h maintained on rations below that which would r e s u l t i n optinu growth rate ( i n this case on rations l e s s than 1.5% per day) may be TABLE V 44 GROSS AND NET GROWTH EFFICIENCY OF FINGERLING  RAINBOW TROUT Age Diet I n f e c t i o n Level K(gross e f f i c i e n c y ) Kn(net e f f i c i e n c y ) 8mo 1% Infected 0.159 0 . 2 4 4 » " Control 0.184 0 . 2 6 6 2% Inf 0 . 1 8 6 0 . 2 4 1 II M Con 0 . 1 8 1 0 . 2 2 « 3% Inf 0 . 1 2 9 0 . 1 5 2 .1 Con 0 . 1 1 9 0 . 1 3 3 k% Inf 0.1 0.111 II II Con 0.111 0 . 1 2 2 45 represented by positive K lines. Fish fed rations greater than the optimum would be capable of metabolic expenditures which outreach their levels of feeding, hence growth efficiencies of these fish would be des-cribed by a negative K line. Accordingly, gross growth efficiency curves obtained i n this study reflect low (positive slope) and intermediate to high (negative slope) ration levels (Kerr, 1971; Brett and Shelbourn, 1975) and adequately describe efficiency-ration relationships representa-tive of control and parasitized trout used i n this investigation.- ' A f i n a l manipulation of growth rate data (Figure 13) compares growth rates of fingerling and 1% year old fi s h on 1% and 3% rations (values for control and infected fish combined) with weight. No significant cor-relations between weight and growth were found, indicating that the allotted rations were not in excess of those required for increasing growth (Brett and Shelbourn 1975) . These data confirm the positive K lines which appear in Fig. 7a. A summary of the relationships between control f i s h and those infec-ted with J_. truttae according to rations fed appears in Fig. 8; growth efficiency vs growth rate. The positive correlations obtained i l l u s t r a t e a basic trend toward increasing growth efficiency with increasing growth rate at a given ration level. Most efficient use of rations occurs where lowest rations are presented. Since these results agree with those pre-sented by Brown (1957), Paloheimo and Dickie (1966b), Kerr (1971), Brett and Shelbourn (1975), and others, and since regression lines representing infected and non-infected fish are virt u a l l y the same, i t may be concluded that there is no significant difference i n growth characteristics betweer 45a Figure 1 3 . Growth rate of fingerling and. 1-jr year old rainbow trout in relation to fish weight. One percent and three percent ration groups only are represented; data from control and infected fish i s combined. 46 47 p a r a s i t i z e d and p a r a s i t e - f r e e trout which may be a t t r i b u t e d to the pre-sence of T_. tr u t t a e . 2. Stamina Experiments Importance of r e l a t i v e condition ( " f i t n e s s " or "condition factor") and morphological measurements i n stamina experiments have been discussed by Bainbridge (1960) for g o l d f i s h , dace and rainbow tr o u t , Brett (1964) and Bams (1967) f o r sockeye salmon, Blaxter (1969) f o r various species of marine f i s h , Webb (1971a,b, 1975) for rainbow trout and Jones et a l . (1974) f o r various species of fresh-water f i s h i n c l u d i n g rainbow trout. These authors suggest that for f i s h with condition factors greater than 1.0 (such as those used i n th i s study), the la r g e r the condition f a c t o r the.less well the f i s h w i l l perform i n swimming tests since f i s h which present more surface area and drag i n stamina chambers (have greater r e -l a t i v e breadth, width, depth and weight to length r a t i o s ) a t t a i n lower c r i t i c a l v e l o c i t i e s and fatigue f a s t e r than f i s h with l e s s surface area and drag. Therefore, s i m i l a r i t i e s i n body morphology and condition factor measurements of a l l f i s h within each r a t i o n category i n t h i s i n v e s t i g a t i o n (Tables 3 and 4), suggest that any differences between observed stamina measurements of p a r a s i t i z e d and control trout are a d i r e c t r e s u l t of the presence of T_. truttae and do not occur as a r e s u l t of d i f f e r i n g condition factors or body shapes of in f e c t e d or non-infected f i s h . C r i t i c a l v e l o c i t y t e s t s , used as a basis by which to compare maximum sustained swimming speeds ( F i g . 9), show that control, and in f e c t e d trout perform equally well at any r a t i o n l e v e l . E f f e c t s of parasites on c r i t i -c a l swimming speeds of f i s h have also been tested by Fox (1965), working 4d with Bolbophorus confusus, a s t r i g e i d trematode whose metacercariae encyst i n the musculature of rainbow trout, Smith and Margolis (1970) and Boyce (pers. comm.), who examined Eubothrium s a l v e l i n i , a tapeworm attached to the p y l o r i c caeca and i n t e s t i n e of sockeye salmon and Butler and Millemann (1971), who studied the trematode Nanophyetus salmincola encysted i n the muscle of coho salmon and steelhead t r o u t . A l l of these i n v e s t i g a t o r s found decreased swimming a b i l i t i e s i n i n f e c t e d f i s h but those working with cercariae noted d e f i c i e n c i e s i n stamina only during migration and encystment of the par a s i t e s . I t i s p o s s i b l e , that had stamina measurements been performed immediately following i n f e c t i o n of the trout with T_. truttae i n this study (while the worms were attaching themselves to and i r r i t a t i n g the caecal mucosa), s i g n i f i c a n t d ifferences i n swimming a b i l i t y between con t r o l and in f e c t e d f i s h may have been found. The data of Smith and Margolis (1970) and Boyce (pers. comm.), however, suggest that i n t e s t i n a l parasites which attach to the mucosa of the p y l o r i c caeca may influence swimming performance regardless of the length of time post i n f e c t i o n that swimming tests are performed. Since none of the above studies examined the e f f e c t s of nematode parasites attached to the i n t e s t i n a l epithelium, i t i s possible that parasites which do not migrate through and destroy the body musculature(as do trematode larvae) or which do not continue to grow to considerable s i z e while wi t h i n the host (as do tapeworms l i k e E_. s a l v e l i n i ) do not e f f e c t the maximum sustained swimming speed of t h e i r host. In addition to the comparison of con t r o l and i n f e c t e d f i s h i n r e l a -t i o n to t h e i r c r i t i c a l swimming speeds, i t i s important to discuss the 49 v a r i a t i o n i n the r e l a t i o n s h i p between length and c r i t i c a l v e l o c i t y be-tween r a t i o n groups. The groups tested which showed the greatest v a r i a -b i l i t y i n s i z e (1% year old f i s h on 1% rations) exhibit a negative r e l a -tionship between length and c r i t i c a l v e l o c i t y such that shorter f i s h perform r e l a t i v e l y better than longer f i s h ( F ig. 9d). These findings have been confirmed by Brett (1964, 1965), Brett and Glass (1973) and Jones et a l . (1974). F i n g e r l i n g trout fed 1%, 2% or 4% rations show no c o r r e l a t i o n between length and c r i t i c a l v e l o c i t y . This i s probably due to s i m i l a r i t y i n s i z e of the f i s h tested. This may imply that when f i s h of nearly the same length (and condition factor) are used i n stamina determinations, v a r i a t i o n s i n i n d i v i d u a l performance w i l l disguise v a r i a -tions i n performance r e l a t i v e to s i z e . In order that a comparison between r e s u l t s of a l l the c r i t i c a l v e l o c i t i e s obtained i n t h i s experiment may be made with values i n the l i t e r a t u r e , mean speeds recorded i n each r a t i o n group are compared with the mean weights and lengths of f i s h used i n the c r i t i c a l v e l o c i t y tests (Figure 14) a f t e r the example of Fry and Cox (1970) . The equations f o r the regression of log e speed (cm/sec) on log e weight (g) were very s i m i l a r for both control and i n f e c t e d f i s h and have been drawn as a s i n g l e l i n e whose equation i s y = 2.49 + 0.84x. S i m i l a r l y the regressions of log e speed on log e length were nearly the same for i n f e c t e d and non-i n f e c t e d f i s h and have been drawn as a single l i n e whose equation i s y = -5.0173 + 0.387x. The speed-weight exponent (0.84) representing the f i s h i n t h i s study i s s l i g h t l y greater than that reported by Blaxter and Dickson (1959), Bainbridge (1960, 1962) and Fry and Cox (1970). Discre-49a Figure 1 4 . C r i t i c a l v e l o c i t i e s attained by f i n g e r l i n g and year o ld rainbow trout i n r e l a t i o n to f i s h length and weight. Mean speeds only of each r a t i o n group tested have been p l o t t e d . Relative c r i t i c a l v e l o c i t i e s (L/sec) of each point p l o t t e d have been included i n order that a comparison with actual swimming speeds (cm/sec) may be made. 50 s p E E D CM 100-90-80-70-60-50-| 40-I SEC 10 I L E N G T H ( C M ) 1 . 1 1 . 2 1? 14 15 16 17 181920 22 24 26 28 30 3o-a ® ^ 3 . 1 5 1 % 3 ! ^ " 3 % 8 MONTH 1 j YEAR 20-B O CONTROL © INFECTED 1 01 ' i t t t"'i t L"T""T* 1 ' I i I1 m ' i "-n 4 5 6 7 8 9 10 15 20 30 40 50 100 200 300 WEIGHT(g) 51 pancies between the r e s u l t s of these i n v e s t i g a t i o n s and those found i n the present study may be a t t r i b u t a b l e to differences i n the types of apparatus used to measure c r i t i c a l v e l o c i t i e s . The stamina chambers used by Blaxter and Dickson (1959), Bainbridge (1960, 1962) and Fry and Cox (1970) were r o t a t i n g annular chambers or doughnut-shaped wheels r o t a t i n g about a c e n t r a l axis i n which both the apparatus and the water were i n motion r e l a t i v e to the f i s h . In t h i s study a flow-through tunnel was used i n which the apparatus and the f i s h were stationary and only the water moved. The speed-length exponent (0.387) obtained i n t h i s i n -v e s t i g a t i o n was s l i g h t l y l e s s than that found f o r sockeye salmon by Brett (1965) and Brett and Glass (1973) and approximately equal to those found for three species of salmonids by Jones et_ al_. (1974) . In addition to the actual c r i t i c a l swimming speeds recorded i n cm/sen, r e l a t i v e c r i t i c a l swimming speeds (recorded i n Lengths/sec) have been i n -cluded for each point d e f i n i n g the speed-weight and speed-length regres-sions p l o t t e d i n Figure 14. Relative swimming speeds (used throughout t h i s study) allow comparison of swimming a b i l i t i e s of f i s h of d i f f e r e n t sizes from d i f f e r e n t populations to be made. Stamina measurements of in f e c t e d and non-infected trout i n t h i s i n v e s t i g a t i o n were compared i n th i s way. I t i s evident from Figure 14 that while l a r g e r f i s h a t t a i n lower r e l a t i v e c r i t i c a l swimming speeds than smaller f i s h , t h e i r actual swimming speeds are greater. These same conclusions about swimming per-formance i n f i s h have been drawn by Bainbridge (1960, 1962), Brett (1964, 1965), Fry and Cox (1970), Brett and Glass (1973), Jones' et a l . (1974), and Webb (1975). Fixed v e l o c i t y t e s t s , conducted at 90% of the c r i t i c a l v e l o c i t y 52 measured f o r f i n g e r l i n g s on 2% rations (Appendix IV) r e v e a l no s i g n i f i -cant diff e r e n c e (p = 0.05) between the c o r r e l a t i o n s of time to fatigue vs v e l o c i t y of control or p a r a s i t i z e d f i s h (Fig. 10). These findings concur with those of K l e i n e_t a l . (1969) , who showed that rainbow trout Infected with Crepidostomum f a r i o n i s swam as well as uninfected c o n t r o l trout, but disagree with those of Butler and Millemann (1971), who ob-tained poorer values for swimming performance from coho salmon and s t e e l -head trout i n f e c t e d with Nanophyetus salmincola than from c o n t r o l s . As has been suggested e a r l i e r , the study of Butler and Milleman (1971) d i f -fered from the present i n v e s t i g a t i o n i n that the aforementioned authors used migrating and encysting trematode cercariae which i n f e c t host muscle t i s s u e , thereby i n f l i c t i n g considerable damage and i r r i t a t i o n on the f i s h . This author used gut-inhabiting nematodes which neither migrate through nor encyst i n muscle t i s s u e . The work of K l e i n et^ al_. (1969) likewise u t i l i z e d a gut-inhabiting p a r a s i t e (a trematode) with no migra-tory or encysting stage. I t i s p o s s i b l e , that i n host-parasite systems such as the one used i n this study and that of K l e i n et^ a l . (1969) , where the d e f i n i t i v e host i s a f i s h , that e f f e c t s of the p a r a s i t e on the w e l l -being of the host are minimal i n order to assure mutual s u r v i v a l and thereby continuance of the parasite l i f e c y c l e . Correlations obtained for time to fatigue vs v e l o c i t y r e l a t i o n s h i p s (Fig. 10) were nearly the same for both control and i n f e c t e d f i s h and do not d i f f e r greatly from established f i x e d - v e l o c i t y test values found by Brett (1964). S i m i l a r l y , no s i g n i f i c a n t differences i n burst v e l o c i t i e s of f i s h maintained on d i f f e r e n t rations were found ( F i g . 11). However, whereas 53 the time maintained-burst v e l o c i t y exponents and maximum burst v e l o c i t i e s attained ( F i g . 11) i n this study are s i m i l a r to those obtained by Blaxter and Dickson (1959), Bainbridge (1960, 1962) and Brett (1964), the duration of the burst swimming a c t i v i t y i n the present i n v e s t i g a t i o n i s very much shorter (1/3 sec) than the durations of burst a c t i v i t y re-corded by the above-mentioned authors (20 sec). The differences i n the time maintained factor of the burst v e l o c i t y measurements may be account-ed for by examination of the methods used by the other i n v e s t i g a t o r s i n r e l a t i o n to those employed i n t h i s study. Blaxter and Dickson (1959) timed f i s h i n open tanks against a reference background, i n culverts and i n tubes towed through the water to get s u b s t a n t i a l flow rates against which f i s h were encouraged to swim. Bainbridge (1960, 1962) employed a r o t a t i n g annular tank i n which f i s h remained stationary r e l a t i v e to the tank. He recorded burst v e l o c i t i e s with an o s c i l l o s c o p e and a movie-camera. Brett (1964) extrapolated data of other i n v e s t i g a t o r s to get the burst v e l o c i t y regression l i n e he presented. A l l apparatus used to com-p i l e the above information on burst swimming allowed t e s t f i s h consider-able freedom of movement, whereas the swimming chamber used i n t h i s study r e s t r i c t e d l a t e r a l and v e r t i c a l movement considerably, e s p e c i a l l y where lar g e r f i s h were used. I t i s possible that had a longer tube with a greater diameter been used for burst v e l o c i t y tests i n t h i s i n v e s t i g a t i o n , times for which burst speeds could be maintained would be comparable to those reported i n the l i t e r a t u r e . No differences i n the r e l a t i o n s h i p between time maintained and maxi-mum burst v e l o c i t y attained by control and inf e c t e d f i s h were found (Fig. 11). While s i m i l a r studies t e s t i n g the burst swimming of p a r a s i t i z e d and 54 c o n t r o l f i s h have not been reported i n the l i t e r a t u r e , and thus cannot provide a comparison with the r e s u l t s of the present work, these r e s u l t s are at l e a s t consistent with those of the other two components of s t a -mina measurement ( c r i t i c a l v e l o c i t y tests and f i x e d v e l o c i t y tests) ex-amined i n this series of swimming experiments. Combination of f i x e d v e l o c i t y ( Fig. 10) and burst v e l o c i t y ( Fig. 11) regressions into a s i n g l e graph ( F i g . 15) gives a more complete estima-t i o n of the approximate swimming a b i l i t i e s of the f i n g e r l i n g trout (mean length 14.9 cm) used i n stamina tests i n this study. Composite swimming curves, obtained by Brett (1964) using sockeye salmon, and Bainbridge (1960, 1962), who tested rainbow trout, have been included i n Figure 15 for comparison. In general, the sustained swimming and steady swimming regressions found i n t h i s i n v e s t i g a t i o n are s i m i l a r to those obtained by the aforementioned authors. Burst swimming regressions calculated f or f i s h used i n t h i s study display slopes s i m i l a r to those found by Bainbridge (1960, 1962) and Brett (1964). Duration of burst swimming a c t i v i t y i n t h i s i n v e s t i g a t i o n was shorter than that measured by the above authors for reasons already discussed. Extension of a l i n e from the t r a n s i t i o n area between the steady swimming and the sustained swimming curves to the y axis ( v e l o c i t y axis) indicates that the average c r i t i c a l v e l o c i t y of the experimental f i s h i s approximately 3.1 lengths per sec. This i s s l i g h t l y lower than the actual measured values for the f i s h used i n t h i s i n v e s t i g a t i o n (Appendix IV) and s l i g h t l y greater than values reported by Brett (1964) . Bainbridge (1962) may have obtained s l i g h t l y lower c r i t i c a l v e l o c i t y estimates than Brett (1964) or the present i n v e s t i g a t i o n d u e to 54a Figure 1 5 . Composite swimming curve relating sustained, steady and burst swimming a b i l i t i e s of fingerling rainbow trout (mean length 1 4 . 9 cm). Included i n the graph for comparison are the data of Brett ( 1 9 6 4 ) , who tested sockeye salmon, and the swimming curves obtained by Bainbridge ( 1 9 6 2 ) for rainbow trout. 1 2 3 4 5 6 7 8 9 10 11 12 VELOCITY (L/SEC'l 56 h i s use of l a r g e r (20-30 cm) rainbow trout (Brett, 1964, 1965; Fry and Cox, 1970). Once accurate determinations of swimming a b i l i t y have been made, and speed-weight r e l a t i o n s h i p s have been established ( F i g . 14), de r i v a t i o n of oxygen consumption and therefore of metabolic rates of exercised f i s h i s p o ssible (Brett and Glass, 1973). Active metabolic rates ( i n mg 0^ consumed/Kg body weight/hr) as defined by Brett (1964, 1965), occur when f i s h reach t h e i r maximum sustained swimming speed ( c r i t i c a l v e l o c i t y ) . Standard metabolic rates (representing 0^ consumption of f i s h at rest or zero a c t i v i t y ) may be obtained by extrapolating 0^ consumption versus v e l o c i t y curves back to zero v e l o c i t y (Fry, 1957; Br e t t , 1965). C r i t i c a l v e l o c i t i e s and speed-weight r e l a t i o n s h i p s , determined f o r f i n g e r l i n g trout and lig year old trout on 1% rations i n this i n v e s t i g a t i o n , resemble c l o s e l y the c r i t i c a l v e l o c i t i e s and speed-weight exponents found by Brett (1964, 1965) for sockeye salmon. Therefore, approximate determinations of active and standard metabolic rates of the trout tested at 10°C i n thi s study may be made (Figure 16) using the temperature-weight response surfaces for active and standard metabolic rates obtained by Brett and Glass (1973). Comparison of act i v e and standard metabolic rates obtained i n t h i s manner (Table VI) shows that smaller f i s h have greater metabolic rates per unit weight than l a r g e r f i s h . Fry (1957), Brett (1964, 1965) and Brett and Glass (1973) have made s i m i l a r observations for weight-metabolic rate r e l a t i o n s h i p s found for a v a r i e t y of fresh and s a l t water f i s h . Subtraction of the standard metabolic rates from the act i v e meta-b o l i c rates obtained above, y i e l d s the "scope for a c t i v i t y " (Fry, 1947) values presented i n Table VI. Scope for a c t i v i t y has been considered as a means to assess environmental stress on fis h e s (Brett, 1958), as an 56a Figure 1 6 . Temperature-weight responses for active and standard metabolic rates of f i n g e r l i n g and 1 £ year old r a i n -bow trout. Data representing f i n g e r l i n g s maintained on 1%, 2%, and k% r a t i o n s and 1^ - year o l d trout fed \% r a t i o n s have been included. V e r t i c a l l i n e s cor-responding to weights of both control and i n f e c t e d f i s h have been drawn to the temperature i s o p l e t h equivalent to the temperature at which swimming t e s t s were conducted ( 1 0 ° C ) . Metabolic rates are given i n mg O2 consumed/hr. Graph i s drawn a f t e r Brett and Glass ( 1 9 7 3 ) . 57 58 TABLE VI ACTIVE AND STANDARD METABOLIC RATES AND SCOPE  FOR ACTIVITY OF FINGERLING AND l £ YEAR OLD RAINBOW TROUT Age Ration Infection Level Mean Wt(g) Metabolic Rate* Scope for Activity Active Standard 8mo 1% Infected 27-75 WT ES 624 » " Control 26.06 690 65 625 " 2% Inf 45.25 685 63 622 " " Con 42.27 685 62 623 " k% Inf 54.5 681 61 620 " • . Con 55-29 681 61 620 i i yr V/o Inf 277.32 655 47 608 " " Con 256.65 652 46 606 *mg 0 ? consumed/ Kg fish tissue/ hr 59 index of energy a v a i l a b l e for swimming i n f i s h (Brett, 1964), and more recently as a means of comparison between responses of d i f f e r e n t s t r a i n s or species of f i s h to temperature and photoperiod f l u c t u a t i o n s , starva-t i o n and the onset of sexual maturity (Dickson and Kramer, 1971). Lower scopes f o r a c t i v i t y i n groups of f i s h i n f e c t e d with parasites such as T_. truttae would therefore i n d i c a t e a reduced amount of energy a v a i l a b l e for swimming or regulation of b o d i l y functions i n response to a changing environment. Examination of the approximate scopes for a c t i v i t y of para-s i t i z e d and control f i s h i n two age categories, at three r a t i o n l e v e l s , tested i n the present i n v e s t i g a t i o n (Table VI), reveals no s i g n i f i c a n t d i f f e r e n c e at the p = 0.05 l e v e l between "scopes" of i n f e c t e d and non-i n f e c t e d f i s h . These r e s u l t s suggest that T_. truttae has no measurable e f f e c t on the a b i l i t i e s of i n f e c t e d f i s h to regulate t h e i r metabolism i n response to environmental changes and confirm the s i m i l a r i t i e s i n swim-ming performance of i n f e c t e d and non-infected trout observed i n t h i s study. Scope for a c t i v i t y values may therefore be useful i n assessing e f f e c t s of parasitism on f i s h . General Conclusion Given the environmental conditions and l e v e l s of p a r a s i t i c i n f e c t i o n used i n this study, the r e s u l t s obtained i n d i c a t e no 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 on growth, swimming performance or metabolic a c t i v i t y of rainbow trout occur as a r e s u l t of i n f e c t i o n with the p a r a s i t i c nema-tode Tru t t a e d a c n i t i s t r u t t a e . Since the trout i s the d e f i n i t i v e host i n which the p a r a s i t e matures and from which the p a r a s i t e c o n t i n u a l l y releases v i a b l e f e r t i l i z e d eggs (evidence from the present investigation) , i t i s 60 reasonable to assume that by not a l t e r i n g or i n t e r r u p t i n g p h y s i o l o g i c a l a c t i v i t i e s e s s e n t i a l to the host's w e l l being, T_. tr u t t a e i s ensuring per-petuation of i t s own l i f e c y c l e . Thus, the findings of Fox (1965), Lester (M.S. 1969) and Butler and Millemann (1971) (parasites e f f e c t stamina and metabolic rate) are not d i r e c t l y comparable with those pre-sented here since these authors measured e f f e c t s of l a r v a l parasites on intermediate (not d e f i n i t i v e ) hosts. Continuance of the l i f e cycles of parasites used i n the above studies would therefore depend on ingestion of the intermediate host by sui t a b l e d e f i n i t i v e hosts ( f i s h eating b i r d s ) . By decreasing swimming a b i l i t y of t r o u t , salmon or stick l e b a c k hosts, l a r v a l parasites may therefore increase t h e i r chances of being ingested by the f i n a l b i r d host they require f o r development into adult p a r a s i t e s . While T_. truttae had no measurable e f f e c t on swimming and growth under the conditions used i n t h i s study, i t i s possible that had a d d i t i o n -a l environmental st r e s s factors (Brett, 1958) been introduced i n t o the experimental design, s i g n i f i c a n t reductions i n growth and swimming e f f i -ciency may have been found. Smith and Margolis (1970) showed that during s m o l t i f i c a t i o n and migration swimming a b i l i t y and growth rates of sockeye salmon i n f e c t e d with Eubothrium s a l v e l i n i were markedly reduced. Rainbow trout i n f e c t e d with 5 to 7 T_. truttae died 60% f a s t e r than non-infected controls when maintained on st a r v a t i o n diets (Hiscox and Brocksen, 1973). Brett (1958) has suggested that f l u c t u a t i n g temperatures, changing s a l i n i -t i e s and alte r e d photoperiods may a l l influence the p h y s i o l o g i c a l state of salmonids, e s p e c i a l l y i f they harbour considerable numbers of pa r a s i t e s . In addition to the above stress f a c t o r s , state of sexual maturity and variance i n s i z e among experimental f i s h ( p o s i t i o n which a f i s h 61 occupies i n the dominance hierarchy established i n the tank (Stringer and Hoar, 1955) may also influence growth and metabolic rates (Brown, 1957). Thus, use of spawning or post-spawning f i s h or i n f e c t i o n only of smaller trout w i t h i n a given population of f i s h may have resu l t e d i n more pronounced decreases i n growth or swimming e f f i c i e n c y i n f i s h i n f e c -ted with J_. t r u t t a e . . In t h e i r d i s c u s s i o n of p o t e n t i a l b i o l o g i c a l and economic e f f e c t s of J_* truttae i n f e c t i o n s , Hiscox and Brocksen (1973) have suggested that the minor decrease i n growth e f f i c i e n c i e s they observed would r e s u l t i n major f i n a n c i a l expenditures i f hatchery trout harbouring these parasites were ra i s e d . While these parasites may indeed be important where a r t i f i c i a l f i s h c u l t u r a l s i t u a t i o n s p r e v a i l (although p a r a s i t i z e d or diseased f i s h are usually eliminated from hatchery systems as soon as they are d i s -covered) , i t i s l i k e l y that i n natural s i t u a t i o n s , environmental and physio-l o g i c a l factors such as food a v a i l a b i l i t y , temperature, photoperiod and state of sexual maturity influence growth and swimming e f f i c i e n c y to a much greater degree. 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Laboratory studies on the feeding, bioenergetics and growth of f i s h , pp. 175-214. In The B i o l o g i c a l Basis of Freshwater F i s h Production. S.D. Gerking (ed.) Blackwell S c i e n t i f i c P u b l i c a t i o n s . Oxford. Webb, P.W. 1971a. The swimming energetics of trout. I. Thrust and power output at c r u i s i n g speeds. J. Exp. B i o l . 55: 521-540. 66 Webb, P.W. 1971b. The swimming energetics of trout. I I . Oxygen consump-t i o n and swimming e f f i c i e n c y . J. Exp. B i o l . 55: 521-540. Webb, P.W. 1975. Hydrodynamics and energetics of f i s h population. F i s h . Res. Board Can. B u l l . 190. 158 pp. Whitlock, J.H. 1949. Co r n e l l V e t e r i n a r i a n 39: 146-182. Wisniewski, L.W. 1932. Zur postenbryonalen entwicklung von Cyathocephalus truncatus. Zool. Anz. 48: 7-8. 67 APPENDIX I EQUATIONS FOR REGRESSION LINES APPEARING IN FIGURES 1, 2. AND 3. Age of Fish Ration Equation of Regression Line Figure 2 Growth Rate vs 8mo 11 1% 2% y= y= 7.32 +(-0.059)x 13.17 +(-0.088)x Number of Para s i t e s t i 3% y= H . 0 5 +(-0.113)x 11 4% y= 16.37 +(-0.11)x I i yr V/o y= 5.94 +(-0.019)x it y/o y= 11.68 +(-0.053)x Figure 3 Food Consumption vs 8mo • i 1% 2% y= y= 41.46 + 0.098x 70.83 +(-0.302)x Number of Para s i t e s it y/o y= 113.72 +(-0.926)x 11 k% y= 147.34 +(-0.254)x l£ yr y= 42.56 + 0.013x II y/o y= 109.83 +(»0.178)x Figure 4. Growth E f f i c i e n c y vs Number of Parasites 8mo 1% y= 18.17 +(-0.0018)X it 2% y= 18.63 +(-0.0005)x it 3% y= 12.43 +(-0.00003)x 11 k% y= 11.12 +(-0.0009)x 1? yr \% y= 13.88 +(-0.00048)x t l y/o y= 10.62 +(-0„00034)x APPENDIX I I EQUATIONS FOR REGRESSION LINES APPEARING IH FIGURE 8 • (GROWTH EFFICIENCY VS GROWTH RATE) Age of Fish Diet I n f e c t i o n Level Equation of Regression Lines* 8mo 1 0/ Infected y = -0.21+ 0.02ifX II il Control y = 9.8+ 0.012x II 2% Inf y = -0.0029+ 0.015x u n Con y = 0.28+ 0 . 0 1 4 X it 3% Inf y = 0+ O.OIx ii H Con y = -0.052+ 0.0086x ti 4% Inf y = 0.026+ 0.0066x it II Con y = 0.0if6+ 0.0068x \% Inf y = -0.207+ 0.051x H ti Con y = 0.0004+ 0.024x H Inf y = -0.034+ 0.0095x ti it Con y = 0.086+ 0.0085x * a l l regressions s i g n i f i c a n t at p= 0.01 APPENDIX I I I EQUATIONS FOR REGRESSION LINES APPEARING IN FIGURE 11 (TIME MAINTAINED VS BURST VELOCITY. FINGERLING FISH) Ration Infection Level Equation of Regression Line 1% Infected y= 0.251+ (-O.OH)x** " Control y= 0.334+ (-0.03)x* y/o Inf y= 0.251+ (-0.022)x* " Con y= 0.269* (-0.025)x* k% Inf y= 0.317+ (-0.026)x* " Con y= 0.276+ (-0.015)x»* *= significant correlation at p= 0.01 **= significant correlation at p= 0.05 70 APPENDIX IV MEAN LENGTHS, WEIGHTS, AND CRITICAL VELOCITIES OF FISH USED IN STAMINA EXPERIMENTS Age Diet I n f e c t i o n Level Mean Lt(cm) Mean Wt(g) Mean C r i t Vel(L/sec) n 8mo 1% Infected 13.34 27.75 3.87 7 it II Control 13.04 26.06 4.12 . 7 ti 2% Inf 15.44 45.25 3.2 8 it it Con 15.03 42.27 3.22 8 it 4% Inf 16.24 54.5 3.15 7 it tt Con 16.33 55-29 3.43 7 1% Inf 27.91 277.32 2.96 7 tt tt Con 27.1 256.65 3.13 7 

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