Implications on growth performance, glucose metabolism, PI 3 K/AKT pathway, intestinal flora induced by dietary taurine in a high-carbohydrate diet for grass carp ( Ctenopharyngodon idella ).

An 8-week experiment was performed to investigate the influence on growth performance, plasma biochemistry, glucose metabolism, and the insulin pathway of supplementation of dietary taurine to a high-carbohydrate diet for grass carp. In this study, fish were fed fish were fed diets at one of two carbohydrate levels, 31.49% (PC) or 38.61% (T00). The high carbohydrate basal diet (T00), without taurine, was supplemented with 0.05% (T05), 0.10% (T10), 0.15% (T15), or 0.20% (T20) taurine, resulting in six isonitrogenous (30.37%) and isolipidic (2.37%) experimental diets. The experimental results showed that optimal taurine level improved significantly weight gain (WG), specific growth rate (SGR), feed utilization, reduced plasma total cholesterol levels (TC), triglyceride (TG) and promoted insulin-like growth factor level (IGF-1). Glucokinase (GK), pyruvate kinase (PK), phosphoenolpyruvate carboxykinase (PEPCK) activities showed a quadratic function model with increasing dietary taurine level, while hexokinase (HK), fatty acid synthetase (FAS) activities exhibited a positive linear trend. Optimal taurine supplementation in high carbohydrate diet upregulated insulin receptor ( Ir ), insulin receptor substrate ( Irs1 ), phosphatidylinositol 3-kinase ( pi3k ), protein kinase B ( akt1 ), Glycogen synthase kinase 3 β ( gs3kβ ) mRNA level; and downregulated insulin-like growth factor ( igf-1 ), Insulin-like growth factor 1 receptor ( igf-1R ), Fork head transcription factor 1 ( foxo1 ) mRNA level. The above results suggested that optimal taurine level could improve growth performance, hepatic capacity for glycolipid metabolism, insulin sensitivity, thus enhancing the utilization of carbohydrates in grass carp. Based on SGR, dietary optimal tributyrin taurine supplementation in grass carp was estimated to be 0.08%.