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 16.8 MJ kg− 1 diet) using corn starch as the carbohydrate source were formulated to contain six carbohydrate levels. Each diet was tested in triplicate for 8 weeks. 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.