utilized for growth. Recent studies on salmonid fishes in aquaria and in 

 artificial streams at Oregon State University have well demonstrated the 

 importance of this effect. An increase of the activity of fish with rise 

 of temperature can, of course, sometimes result in greatly increased exploi- 

 tation of available food resources. However, much improvement of foraging 

 efficiency may not be possible because of the nature of the food supply and 

 of the feeding habits of the fish. The effect of a temperature increase on 

 growth in the natural environment than can be just the opposite of that ob- 

 served in laboratory tests when the food supply is unlimited. Since the 

 gross efficiency of conversion of a limited amount of food is reduced at an 

 elevated temperature at which the appetite for food is increased, there is 

 superficial similarity between the thermal effects and those of poisons 

 that impair metabolism while stimulating the appetite. Obviously, however, 

 there are important physiological differences of these effects that should 

 be recognized. Growth is more likely to be impaired markedly by a rise of 

 temperature when uniformly restricted food supplies are small than when the 

 daily rations are relatively large. 



Although deposits of fat can be of great value to fish during periods 

 of nutritional deficiency, mere deposition of fat should be distinguished 

 from true growth, which is largely an increase of protein. Appropriate 

 measurements of body composition should be made, therefore, in connection 

 with studies of growth. Finally, I want to point out that low concentra- 

 tions of some poisons may not only be harmless to fish in nature but also 

 favor growth. There is some evidence that the vigor and foraging 

 efficiency of fish, as well as their appetite, increase at low levels of 

 some substances that generally are regarded as poisons only, so that growth 

 may be promoted not only under artificial conditions. Such data should not 

 be judged obviously erroneous. 



REFERENCES 



Brake, L.A. 1972. Influence of dissolved oxygen and temperature on the 

 growth of juvenile largemouth bass held in artificial ponds. M.S. 

 Thesis. Orgeon State Univ., Corvallis, Ore. 



Broderius, S.J. 1970. Determination of molecular hydrocyanic acid in water 

 and studies of the chemistry and toxicity to fish of the nickelocyanide 

 complex. M.S. Thesis. Oregon State Univ., Corvallis, Ore. 



Chapman, G.A. 1965. Effects of sub-lethal levels of pentachlorphenol on 

 the growth and metabolism of a cichlid fish. M.S. Thesis. Oregon State 

 Univ., Corvallis, Ore. 



Davis, G.E., and C.E. Warren. 1968. Estimation of food consumption rates, 

 In W.E. Ricker (ed.) Methods for assessment of fish production in fresh 

 waters. Intern. Biol. Prog. Handb. 3. Blackwell Scientific Publica- 

 tions, Oxford, p. 204-225. 



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