The Relation Between Growth and Food Consumption in the Brown Trout (Salmo Trutta)

1. The growth of brown trout (Salmo trutta), fed on Gammarus pulex, in their first and second years has been studied. 2. The growth in weight varies considerably from week to week but, generally speaking, it increases with increasing size of the fish. It is assumed that in these experiments the second point of inflection of the normal S-shaped growth curve was not reached because the fish were too young. 3. In all the fishes studied there was a period of slow growth during the winter and during the summer. Growth is at its maximum at temperatures between 50 and 60° F. 4. By careful adjustment of the rations it was possible to keep the body weight of the fish approximately constant from week to week. The amount of food required for this purpose varied from 51 to 270 mg./g. of body weight per week, but was mainly between 70 and 102 mg. and was apparently affected by the water temperature, being higher when the water was warmer. 5. Starved fish lost more weight at higher temperatures than at lower, but the loss of weight could not be related to the amount of food required to maintain the body weight constant at a given temperature. 6. The appetite of fully fed fish increases as the temperature rises to 60° F. but generally declines at temperatures higher than this. Between 40 and 50° F. the amount of growth made is roughly directly proportional to the amount of food eaten, but above 50° no such simple relation exists. 7. G. pulex is a very efficient food for trout; generally speaking about 5 g. of this food produce 1 g. increase in weight. If from this amount the quantity required to maintain the body weight constant is subtracted, it is found that 1 g. increase in weight is produced by about 3 g. of food available for growth. 8. The average weight of the Gammarus used as food in this experiment was 0.026 g., and it is estimated that for every gram increase of weight each fish consumed between 200 and 300 Gammarus.