Effects of Replacing Soybean Meal With Degossypolized Cottonseed Protein on the Growth Performance, Protein Metabolism, Digestive Capacity, and Antioxidant Capacity of Hybrid Fish Hefang Bream

An 8‐week feeding trial was conducted to evaluate the feasibility of substituting soybean meal (SBM) with degossypolized cottonseed protein (DCP) on Hefang bream. Five iso‐nitrogenous and iso‐lipidic diets were formulated with graded replacement levels of SBM by DCP at 0% (control), 25% (DCP25), 50% (DCP50), 75% (DCP75), and 100% (DCP100). Results showed that DCP could effectively replace up to 50% of dietary SBM in Hefang bream, without adverse influence on survival rate and growth performance. However, the specific growth rate in fish fed diets with DCP replacing 75% and 100% of SBM decreased significantly. Muscle essential amino acid profiles showed marked reductions in isoleucine, leucine, and lysine concentrations in fish fed diets with DCP replacing 75% and 100% of SBM, correlating with suppressed mTOR pathway transcription. The intestinal villi length and the intestinal trypsin activity in fish fed diets with DCP replacing 75% and 100% of SBM were significantly lower than those in the control group. The total antioxidant capacity and catalase activity in fish fed the diet with DCP replacing 100% of SBM were significantly lower than those in the control group. The mRNA expression of hepatic inflammatory cytokines in fish fed the diet with DCP replacing 25% of SBM was the lowest among the groups. In conclusion, these findings suggest that DCP can replace up to 50% of SBM in diets of the Hefang bream without compromising the growth performance. However, excessive dietary DCP (75%–100%) can induce protein utilization impairment, digestive dysfunction, oxidative stress, and hepatic inflammation.