Riboflavin requirement for growth, tissue saturation and maximal flavin-dependent enzyme activity in young rainbow trout (Salmo gairdneri) at two temperatures.

Two temperatures (10 degrees and 15 degrees C) and two fish stocks differing in growth potential were used to determine the dietary riboflavin requirement of young rainbow trout (Salmo gairdneri) on the basis of growth parameters, tissue saturation and a flavin-dependent biochemical function. Two experiments were conducted with purified diets based on vitamin-free casein. In experiment 1, fry (initially 2.0 g/fish) were fed, for 16 wk at 15 degrees C, diets containing 0.6, 2.6, 3.6, 4.6, 5.6 or 6.6 mg riboflavin per kilogram diet. In experiment 2, fry (initially 1.7-1.8 g/fish) were held at either 10 degrees or 15 degrees C and fed, for 10 wk, diets containing 0.7, 2.7, 3.7, 4.7, 6.7 or 8.7 mg riboflavin per kilogram. The riboflavin requirements for maximal growth rate, liver flavin saturation, spleen and head kidney flavin saturation and maximal hepatic D-amino-acid oxidase activity were 3.6, 4.6, 6.6 and 5.6 mg/kg diet, respectively, in a diet containing 40% crude protein and 15% ether extract. The requirements were not affected by temperature or by genetically determined differences in maximal growth rate. When expressed on a dietary energy basis, the riboflavin requirements of the trout for maximal growth rate and liver flavin saturation appear similar to those of several homeothermic species.