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.