Effects of dietary protein and lipid levels on growth of bullfrog( Rana catesbeiana)

A feeding trial was conducted to estimate the optimum dietary protein and lipid levels for bullfrog( Rana catesbeiana).Twelve diets were formulated to contain three protein levels(35%,40% and 45%),each with four lipid levels( 4%,7%,10% and 13%),in order to produce a range of P /E ratios( from 21. 9 to 32. 0mg protein /kJ). The designed dietary protein and lipid levels in a brown fish meal-based formulation were achieved by serial adjustment of casein( for protein) or a mixture of fish oil and soybean oil( for lipid) at the expense of microcrystalline cellulose. Each diet was randomly assigned to three tanks( 200 L),each tank was stocked with 12 bullfrogs[( 91. 5 ± 0. 10) g average initial body weight]. Bullfrogs were fed twice daily( 08: 00and 17: 00) to apparent satiation for 8 weeks. The results showed that no significant differences in survival were found among all dietary treatments,but bullfrogs fed the diet with 13% lipid displayed liver lesions,such as abnormal color and crumbly texture. Weight gain( WG) and specific growth rate( SGR) of bullfrogs fed diet with 40% protein were significantly higher than those of bullfrogs fed diet with 35% protein( P 0. 05),but there were no significant differences with bullfrogs fed diet with 45% protein( P 0. 05). With increasing dietary protein levels,feed efficiency( FE) increased significantly,whereas,feed rate( FR) and protein efficiency ratio( PER) were just the opposite( P 0. 05). WG,SGR and FR increased significantly with increasing dietary lipid levels( P 0. 05),however,FE,PER and nitrogen retention were not significantly affected by dietary lipid levels( P 0. 05). No significant difference was observed in body composition among all the groups at different dietary protein levels( P 0. 05). Whole-body crude protein contents were not significantly affected by dietary lipid levels( P 0. 05). However,whole-body crude lipid and energy contents increased significantly with increasing dietary lipid level( P 0. 05). With increasing dietary lipid levels,hepatic malondialdehyde( MDA)concentration increased significantly,whereas,hepatic catalase( CAT) and lipoprotein lipase( LPL) activity were first increased and then decreased( P 0. 05). The results of this study suggest that diet containing 40% protein and 7% lipid with a protein to energy ratio of 27. 7 mg protein /kJ is optimal for bullfrog.