Optimal dietary carbohydrate to lipid ratio for bullfrog Rana (Lithobates) catesbeiana

This study aimed to investigate the optimum dietary carbohydrate/lipid (CHO/L) ratio for bullfrog Rana (Lithobates) catesbeiana . Six isonitrogenous and isoenergetic diets were formulated, containing various CHO/L from 1.20 to 12.11. Bullfrogs were fed six diets for 8 weeks and each diet was tested by three replicates. After the 8 weeks feeding, weight gain and specific growth rate increased significantly as dietary CHO/L ratios decreased, but showed little difference ( P  > 0.05) as dietary CHO/L ratios ranged from 1.20 to 2.76. Nitrogen retention was significantly affected by CHO/L ratios, and bullfrog fed with CHO/L 6.10 and 1.82 diets showed the lowest and highest nitrogen retentions respectively. Energy retention increased significantly as dietary CHO/L ratios decreased and bullfrog fed the CHO/L at 1.82 and 1.20 diets showed the highest value. Whole‐body lipid and energy levels both increased significantly ( P  <   0.05) as dietary CHO/L ratios decreased. Moreover, liver lipid content of bullfrog fed CHO/L 1.82 and 1.20 diets were significantly higher than that of other groups. Plasma insulin level significantly increased as the elevation of dietary CHO/L. Malondialdehyde level increased as the CHO/L decreased, and the bullfrog fed the CHO/L 1.20 diet had the highest level. In conclusion, the present results clearly showed the effects of dietary CHO/L ratios on growth; the optimum CHO/L is 2.07 (approximately 22.49% carbohydrate and 10.83% lipid) based on the second‐order polynomial regression analysis of weight gain.