Influence of dietary biotin level on growth, metabolism and pathology of rainbow trout.

Supplementation of a dry diet containing herring and soybean meals with D biotin had no effect on the feed comsumption, growth or mortality of rainbow trout in a 28 week experiment. In a second experiment two series of diets were used: practical, based upon herring and soybean meals, and purified, based upon casein and gelatin. The basal levels of biotin in the two series of diets were: 0.51 and 0 mg/kg, respectively. There were four treatment groups in each of the two diet series: the practical diets were either supplemented with 0.5 mg D biotin/kg or 10% of either raw or heated egg white was added to the diet. The purified diets were supplemented with graded levels of D biotin (0, 0.25 0.5, or 1.0 mg/kg). Raw egg white (1%) was added to the biotin unsupplemented diet. Feeding these diets to rainbow trout for 24 weeks showed that both the practical diet containing egg white, and the unsupplemented, purified diet were biotin deficient, all the other diets contained adequate amounts of biotin to support growth and prevent mortality. Neither supplementation of the practical diet nor adding more than 0.25 mg D biotin/kg to the purified diet resulted in any improvement in growth however the biotin levels in the livers were greater for the fish which had received the higher levels of dietary biotin, but these increased levels of biotin did not influence the activity of acetyl CoA carboxylase. The biotin deficient fish were anorexic, and exhibited degeneration of the gills: shortening and thickening of the lamellae and hypertrophy and hyperplasia of the heterogenous epithelial cells of the lamellae.