The Growth of Brown Trout (Salmo Trutta Linn.)

Abstract

Groups of 100 trout fry were grown in identical aquarium tanks at constant temperatures, with 12 hr. of illumination per day, constant rate of water flow, aeration and composition of the water. Two different temperatures, three different types of food and four levels of feeding were investigated. Individual lengths were recorded for the first 11 weeks after the beginning of feeding. The trout fry took live Tubifex worms eagerly and grew well up to a certain size, when they began to develop bleeding from the fins and dilation of cutaneous blood vessels and to die. It is suggested that Tubifex either lacks some chemical substance essential for trout survival or contains some substance which is accumulative poison. The trout fry which were fed with shrimp meal lost condition and showed poor survival and growth, suggesting that their diet lacked some necessary constituent. These fish developed orange pigment in their caudal and adipose fins; such orange pigment was not developed by fry fed with Tubifex or with liver. The trout fry which were fed with liver had the lowest mortality and showed the best growth, supporting the view that liver contains all the substances necessary for trout growth. Fry fed twice daily with liver showed less enthusiasm for their food than those fed once daily but the former grew slightly faster. Fry fed three or four times per week with liver gorged themselves whenever they were fed but grew at lower rates than those fed daily. Trout fry allowed to eat as much liver as they would once per week gorged themselves, but obtained less than their maintenance requirements and began to die of starvation after 4 weeks at 12.5° C. They were able to grow slowly when fed twice per week. Fry fed once or twice daily with liver grew larger than those thus fed with Tubifex, and the latter grew larger than fry fed daily with shrimpmeal. There were no significant differences in size which could be correlated with diet among fish fed less often than once daily. Trout fry fed daily at 10.5° C. grew more slowly than those fed daily at 12.5° C., but those fed less frequently showed no differences in growth rate which could be associated with temperature. Those fed with Tubifex at 10.5° C. showed a delay of 2 weeks in the onset of high mortality compared with those at 12.5° C.