Effect of dietary carbohydrate levels on growth performance, body composition, intestinal and hepatic enzyme activities, and growth hormone gene expression of juvenile golden pompano, Trachinotus ovatus

A growth trial was conducted to determine the optimum dietary carbohydrate level of juvenile golden pompano (Trachinotus ovatus). Six isonitrogenous and isoenergetic experimental diets (43% crude protein and 16.8MJkg−1 diet) using corn starch as the carbohydrate source were formulated to contain six carbohydrate levels. Each diet was tested in triplicate for 8weeks. Weight gain, specific growth rate, feed intake, protein efficiency ratio, hepatosomatic index, and viserosomatic index increased significantly as dietary starch levels increased from 0% to 16.8% (P<0.05). The feed conversion ratio decreased significantly as dietary starch levels increased from 0% to 16.8% but increased as the level increased from 16.8% to 28%. Whole-body lipid and ash contents decreased significantly as dietary carbohydrate levels increased, whereas the moisture content showed the opposite trend (P<0.05). Whole-body protein contents were not statistically different (P>0.05) among all treatments. Carcass lipid content decreased but carcass protein content increased significantly as dietary carbohydrate levels increased (P<0.05). Both moisture and ash contents of the carcass did not differ significantly (P>0.05) among all treatments. Glycogen content in muscle and liver increased significantly as dietary carbohydrate levels increased (P<0.05). Plasma glucose level increased and plasma cholesterol and triglyceride concentrations decreased significantly as dietary carbohydrate levels increased (P<0.05). The intestinal amylase, alkaline phosphatase, and Na+, K+-ATPase activities all increased with dietary carbohydrate levels up to 11.2% (P<0.05). However, lipase activity decreased significantly as dietary carbohydrate levels increased. There were no significant differences in intestinal protease activities among all treatments (P>0.05). Hepatic hexokinase activity increased and hepatic glucose-6-phosphatase activity decreased significantly as dietary carbohydrate levels increased (P<0.05). Hepatic phosphoenolpyruvate carboxykinase, pyruvate kinase, and malate dehydrogenase activities did not differ among the treatments (P>0.05). Expression of hepatic growth hormone (GH) gene was positively related to growth performance. In conclusion, results suggested that the optimum carbohydrate level for juvenile golden pompano could be 11.2–16.8% of the diet.