Effects of Dietary Carbohydrate-to-lipid Ratio on Growth Performance, Body Composition, Digestive Enzyme Activities, and Hepatic Enzyme Activities in Juvenile Large Yellow Croaker, Larimichthys crocea

An 8-wk feeding trial was conducted to investigate the effects of dietary carbohydrate-to-lipid ratios (CHO:L) on growth performance, body composition, digestive enzyme activities, and hepatic enzyme activities of juvenile large yellow croaker, Larimichthys crocea. Six isonitrogenous (45% crude protein) and isoenergetic (18kJ/g gross energy) diets with varying CHO:L ratios (0.07, 0.48, 1.20, 2.19, 4.81, and 10.48) were fed to triplicate groups of large yellow croaker in floating sea cages. Results showed that the highest specific growth rate (SGR) was found in fish fed diets with CHO:L ratio of 2.19. Fish fed the lower (0.07 and 0.48) CHO:L ratios tended to produce lower growth (P<0.05). The whole-body lipid content significantly decreased, while hepatosomatic index, liver glycogen content, and plasma glucose concentration significantly increased as dietary CHO:L ratios increased (P<0.05). Plasma total cholesterol, triglyceride, and low-density lipoprotein cholesterol concentrations significantly decreased with elevated dietary CHO:L ratios (P<0.05). The increasing dietary CHO:L ratios significantly stimulated the activities of intestinal amylase and hepatic pyruvate kinase and depressed the activity of hepatic phosphoenolpyruvate carboxykinase (P<0.05). Based on a second-order polynomial regression analysis of SGR, 2.38 was determined as the optimal dietary CHO:L ratio for juvenile large yellow croaker.