Effects of feed protein levels on gonadal development in female Aquarana catesbeiana

As an important economic aquaculture species, the 1 Aquarana catesbeiana industry faces challenges in high-quality seedling production, where broodstock nutrition, especially dietary protein level, is a key factor affecting gonadal development and reproductive performance. However, the optimal dietary protein requirement for female A. catesbeianus during the broodstock stage remains unclear. This study aimed to investigate the effects of dietary protein levels on gonadal development in female A. catesbeiana and determine the optimal protein requirement for broodstock cultivation.Five isoenergetic diets were formulated with fish meal and soy protein concentrate as the main protein sources, containing 38%, 41%, 44%, 47%, and 50% crude protein, respectively. A total of 225 healthy female A. catesbeiana with an initial body weight of (172.63±5.00) g were randomly divided into 5 groups with 3 replicates each, and fed for 78 days. Growth performance, gonadal development, egg quality, and serum sex hormone levels were measured at the end of the feeding trial.Dietary protein level significantly affected growth performance, gonadal development, and egg quality of female A catesbeiana. Weight gain rate and feed efficiency increased first and then decreased with increasing dietary protein level, peaking in the 44% group, which was significantly higher than that in the 38% group. The quadratic regression analysis showed that the optimal dietary protein level for growth was 46.08%. The gonadosomatic index (GSI) reached the maximum in the 44% protein group. The black egg rate, absolute fecundity, and egg diameter in the 44%-47% groups were significantly higher than those in the 38% and 41% groups. The serum estradiol (E₂) and progesterone (P₄) levels were the highest in the 47% group. Based on GSI, black egg rate, and absolute fecundity, the optimal dietary protein level for gonadal development was estimated to be 44.05%-46.59%.Both insufficient and excessive dietary protein levels inhibited growth performance and gonadal development of female A. catesbeiana. The optimal dietary protein level for broodstock cultivation is 44.05%–46.59%.These results provide a theoretical basis for the precise formulation of special diets for A catesbeiana broodstock, which is of great practical significance for improving broodstock quality and ensuring the healthy and sustainable development of the bullfrog seedling industry.