Effects of dietary carbohydrate/lipid ratios on growth performance, body composition and glucose metabolism of fingerling blunt snout bream Megalobrama amblycephala

This study aimed to investigate the optimum dietary carbohydrate/lipid (CHO/L) ratio for fingerling blunt snout bream Megalobrama amblycephala (average initial weight: 6.61 +/- 0.03g). Six isonitrogenous and isoenergetic diets were formulated to contain various CHO/L ratios ranging from 1.62 to 24.20. Each diet was tested in four replicates for 10weeks. Specific growth rate (SGR), feed conversion ratio and nitrogen and energy retention all improved significantly (P<0.05) as dietary CHO/L ratios decreased from 24.20 to 5.64 but showed little difference (P>0.05) as dietary CHO/L ratios ranged from 2.45 to 5.64. Hepatosomatic index increased significantly (P<0.05) as dietary CHO/L ratios increased, whereas intraperitoneal fat ratio showed an opposite trend (P<0.05). Opposite to moisture content, lipid content of whole body and carcass all increased significantly (P<0.05) as dietary CHO/L ratios decreased. Liver lipid content showed little difference (P>0.05) among all the treatments, while liver glycogen content increased significantly (P<0.05) with increasing CHO/L ratios. High dietary carbohydrate enhanced the activities of liver hexokinase, pyruvate kinase and glucose-6-phosphate dehydrogenase but did not induce hyperglycaemia. Based on the second-order polynomial regression analysis of SGR, the optimal dietary carbohydrate and lipid contents for fingerling blunt snout bream were 291.7 and 81.4g kg(-1), respectively, with a corresponding dietary CHO/L ratio of 3.58.