Interactive effects of dietary biotin and carbohydrate on growth performance and glucose metabolism in juvenile turbot Scophthalmus maximus L.

A 10-week feeding trial was conducted to explore the effects of dietary biotin and carbohydrate and their interactions on the growth performance and glucose metabolism in juvenile turbot (Scophthalmus maximus L.). Six isonitrogenous and isolipidic diets from a 2 x 3 factorial design was formulated with two levels of carbohydrate (16% and 25%) and three levels of biotin (0 mg/kg, 0.25 mg/kg and 1.5 mg/kg) respectively. The results showed that juvenile turbots fed with 16% of dietary carbohydrate and 1.5 mg/kg of biotin had the highest specific growth rate (SGR) and higher activities of intestinal amylase and stomach pepsin. Dietary biotin lowered the postprandial plasma glucose at 9 h and 24 h, regardless of dietary carbohydrate levels. However, postprandial plasma glucose at 24 h in groups with 25% of dietary carbohydrate was consistently higher than those in groups with 16% of dietary carbohydrate, regardless of dietary biotin levels. In conclusion, dietary biotin significantly decreased plasma glucose by increasing insulin level in plasma, activating PI3K (phosphoinositide 3-kinase)/AKT (protein kinase b) signaling pathway, promoting glucose transportation, glycolysis, pentose phosphate pathway and glycogen synthesis but inhibiting gluconeogenic pathway. Compared with the increased plasma glucose and growth inhibition in juvenile turbot caused by excessive dietary carbohydrate level (25%), however, the hypoglycemic effect of biotin is limited.