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 ± 0.03 g). 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 10 weeks. 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 81.4 g kg⁻¹, respectively, with a corresponding dietary CHO/L ratio of 3.58. [ABSTRACT FROM AUTHOR]