**Background:** Fishmeal (FM) is the primary protein source in aquaculture diets but is becoming scarce and expensive. Plant proteins like soybean meal (SBM) and rapeseed meal (RSM) are potential alternatives, but their effects on broodstock reproduction are not well understood. This study aimed to evaluate how different dietary protein sources affect the reproductive performance and endocrine function of female yellow catfish (Pelteobagrus fulvidraco) broodstock.
**Methods:** Three semipurified diets were formulated using FM, 30% SBM, or 30% RSM as the main protein sources, with casein as a base. The crude protein level was set at 46% across all diets. A total of 270 healthy female yellow catfish (initial weight: 64.56 ± 0.45 g) were equally distributed into 9 net cages (1.0 m × 1.0 m × 1.0 m) with three replicates per treatment. Fish were fed to apparent satiation twice daily for six weeks. At the end of the trial, females were sampled for morphological parameters, body composition, plasma biochemical indexes, and hormone levels. Artificial reproduction was performed using hormone injection (20 ng domperidone, 16 μg LHRH-A2, and 1500 IU HCG per kg body weight). Reproductive performance metrics included gonadosomatic index (GSI), relative fecundity, total egg production, egg diameter, fertilization rate, and hatching rate. Plasma hormones (E2, VTG, LH, FSH, T) were measured by ELISA. Gonadal mRNA expression of steroidogenesis-related genes (StAR, sf-1, 3β-hsd, 17β-hsd, 20β-hsd, cyp11a1, cyp17a1) was quantified by RT-qPCR. Hepatic lipidomics was performed using LC-MS, and gonadal cortisol concentrations were measured by LC-MS/MS.
**Key Results:** No significant differences were found in growth (FBW, SGR) among groups. The SBM group showed significantly higher GSI, relative fecundity, total egg production, egg diameter, and hatching rate compared to the FM group (P < 0.05). No significant difference in fertilization rates was observed among groups. Plasma E2, VTG, and LH were significantly higher in both SBM and RSM groups compared to FM, while T and FSH were significantly lower (P < 0.05). The SBM group had significantly lower gonadal mRNA expression of StAR, sf-1, 3β-hsd, 17β-hsd, 20β-hsd, cyp11a1, and cyp17a1 compared to FM (P < 0.05). The RSM group only showed downregulation of StAR. Both SBM and RSM groups had significantly lower plasma TC and T-Bil and higher GLU and Ca2+ compared to FM (P < 0.05). The SBM group had the highest HDL-C and lowest AST and ALT (P < 0.05). Hepatic lipidomics revealed that SBM and RSM diets increased DG, FA, DGDG, and CL contents but decreased ChE contents in the liver (P < 0.05). The FM group had the highest MFI (9.66 ± 0.41%) and the lowest BL (152.38 ± 2.10 mm). Gonadal cortisol concentrations were significantly lower in the RSM group than in the SBM group (P < 0.05) and extremely significantly lower than in the FM group (P < 0.01).
**Clinical Implications:** This study demonstrates that 30% dietary SBM can effectively replace a portion of FM in yellow catfish broodstock diets without compromising growth and with significant improvements in reproductive performance. The enhanced secretion of E2 and VTG, along with hypocholesterolemic effects, suggests that SBM positively regulates the endocrine system and lipid metabolism. These findings support the use of SBM as a sustainable and cost-effective alternative protein source in broodstock feeds for aquaculture. However, the dose-dependent effects of soy isoflavones warrant further investigation, as higher inclusion levels may have negative effects on reproduction.