Dietary biotin requirements of young rainbow trout (Salmo gairdneri) determined by weight gain, hepatic biotin concentration and maximal biotin-dependent enzyme activities in liver and white muscle.

The objective of the present work was to determine the dietary biotin requirements of young, rapidly growing rainbow trout according to independently measured parameters. Two experiments were conducted with a purified diet which had a basal biotin level of 0.01-0.02 mg/kg. A third study was done with a nonpurified diet with or without a supplement of 1.0 mg biotin/kg. Each study was initiated with fry weighing less than 2 g/fish, and was continued for 16-20 wk at 15 degrees C. The first experiment, a cross-over design with pair-feeding, showed that the unsupplemented purified diet produced a biotin-specific deficiency condition in the trout. Dietary requirements could therefore be estimated (expt 2): maximal weight gain and maximal liver biotin concentration, 0.08 mg/kg; maximal activity of hepatic pyruvate carboxylase and acetyl CoA carboxylase, 0.05 mg/kg; and maximal white muscle pyruvate carboxylase activity, 0.14 mg/kg. No differences were found between fish fed the supplemented nonpurified diet and fish fed its unsupplemented counterpart (expt 3). The biotin requirement of the trout for growth does not exceed that of other vertebrates. These results also raise a question as to the level of supplementation which may be necessary for trout diets under field conditions.