Evaluation of yeast hydrolysate as a substitute to dietary fish meal of| juvenile Jian carp (Cyprinus carpio var. Jian): Protein synthesis via TOR pathway

This study was performed to evaluate effects of fish meal replacement by yeast hydrolysate (YH) on crude protein via TOR pathway of Jian carp, Cyprinus carpio var. Jian (initial average weight 19.44 +/- 0.06 g). Six hundred fish were assigned into five groups and fed with five isonitrogenous and isocaloric diets replacing fish meal by 0g/kg (G1), 10g/kg (G2), 30g/kg (G3), 50g/kg (G4) and 70g/kg YH (G5). The results showed crude protein of fish in G2 and G3 were significantly higher (p < .05) than in G1. YH significantly increased AST and ALT activities of hepatocytes (p < .05) compared with the control group, but had no effects (p > .05) on AST and ALT contents in conditioned medium of hepatocytes. Furthermore, MyoD, TOR and S6K1 mRNA levels in muscle of G2 and G3 were significantly higher than of G1 (p < .05). Meanwhile, YH significantly increased MyoD, TOR and S6K1 mRNA levels in hepatocytes compared with the control group. In conclusion, 10g/kg and 30g/kg YH increased crude protein content of muscle in fish and increased TOR pathway genes expression levels in muscle and hepatocytes.