Optimal dietary protein-to-lipid ratio for the growth and metamorphosis of bullfrog (Aquarana catesbeianus) tadpoles

An 11-week feeding trial was conducted to evaluate the effects of dietary protein-to-lipid ratio on growth performance, feed utilization, antioxidant, and metamorphosis of bullfrog ( Aquarana catesbeianus ) tadpoles. Nine diets were formulated to contain three crude protein levels (DP) (37, 42, and 47 %) and three crude lipid levels (DL) (7, 11, and 15 %). Tadpoles (stage 25, average body weight 0.005 g) were randomly allotted to 27 aquaria (30 L), nine treatments with triplicate groups, 34 tadpoles per replicate. Feeding occurred twice daily, with the total amount equaling 6.50 % of the tadpole’s body weight. The results showed the interaction DP × DL significantly affected survival, FCR, PER, the metamorphosis rate and the liver SOD and CAT activities of the tadpoles. The significant enhancement of weight gain (WG), contents of insulin like growth factor 1 (IGF-1) and growth hormone receptor (GHR) in the liver, content of amphibia thyroxine (T4) in serum, apparent digestibility of dry matter and gross energy, intestinal trypsin activity (TPS) and intestinal lipase capacity (LPS), and metamorphosis rate at stage 40 with increasing DP from 37 % to 47 % and increasing DL from 7 % to 15 % respectively. Significant increases in total cholesterol (T-CHO) and triglyceride (TG) in serum and lipoprotein lipase (LPL) concentration in the liver were observed by increment of DL. Poor growth performance and lower metamorphosis rate at DL of 7 % and DP of 37 %, respectively. There was no significant difference in the metamorphosis rate at stage 40 of bullfrog tadpoles fed with 11 % DL and 15 % DL diets. Whereas compared to the 11 % DL groups, 15 % DL groups significantly reduced the survival rate and liver antioxidant capacity and increased the MDA content. Both the groups fed with 47 P/11 L and 42 P/11 L diets demonstrated favorable growth performance and metamorphosis outcomes. Consequently, based on comprehensive evaluation of survival rate, growth, and liver health of bullfrog tadpoles, 42 P/11 L has been identified as the optimum protein-to-lipid ratio in diets for bullfrog tadpoles. • Dietary protein- lipid levels affected growth and metamorphosis in bullfrog tadpoles. • High lipid (15 %) reduced survival and liver antioxidant capacity while increasing MDA content. • The 42 P/11 L and 47 P/11 L are sufficiently support growth and metamorphosis in bullfrog tadpoles. • The 42 P/11 L diet is recommended as a more cost-effective strategy.