Effect of dietary carbohydrate-to-lipid ratio on growth, blood biochemical indices,hepatic metabolic enzymes and PEPCK gene expression of juvenile obscure puffer(Takifugu obscurus)

This experiment was conducted to evaluate the effects of dietary carbohydrate-to-lipid ratio on growth performance, feed utilization, biochemical indices and phosphoenolpyruvate carboxykinase(PEPCK)gene expression in juvenile obscure puffer, Takifugu obscurus.Six isonitrogenous and isoenergetic diets were formulated with dietary CHO:L ratios of 4.29, 2.79, 1.86, 1.19, 0.73 and 0.42, respectively.Fish(initial weight 11.2±0.5 g)were stocked in triplicate tanks(25 fish per tank)and fed to satiation during a period of 60 days.The results indicated that best specific growth rate, protein efficiency ratio and feed efficiency were found in fish fed diet with CHO:L of 1.86, which were significantly higher than those of fish fed diets with 0.42, 0.73 and 4.29(P<0.05).Plasma triglyceride and liver lipid content increased significantly as dietary CHO:L ratio decreasing(P<0.05), while plasma glucose and hepatic glycogen content showed a contrary tendency.Activities of lipase, fatty acid synthase, amylase and pyruvate kinase in liver were significantly affected by dietary CHO:L ratio(P<0.05).Fish fed diets with CHO:L of 0.42 and 0.73 had significantly higher PEPCK activity and mRNA relative expression than those fed with the other diets(P<0.05).However, survival and plasma total cholesterol content were unaffected by dietary CHO:L ratio.The optimal range of CHO:L within 2.01-2.16 is suitable for juvenile obscure puffer based on second-order polynomial regression analysis of SGR, PER and FE against dietary CHO:L ratio, respectively.