Threshold effects of dietary cottonseed protein concentrate substitution for fishmeal on growth, antioxidant capacity and metabolic regulation in spotted seabass (Lateolabrax maculatus)

This study evaluated cottonseed protein concentrate (CPC) as a partial fishmeal substitute in spotted seabass ( Lateolabrax maculatus ). In a 60-d feeding trial, 400 fish (initial weight 50.91 ± 2.24 g) were randomly assigned to five diets in which fishmeal was replaced by CPC at 0, 15%, 30%, 45%, and 60%. Growth, body composition, muscle quality, antioxidant capacity, and metabolic responses were examined. Results showed that replacing up to 45% of fishmeal with CPC did not significantly affect specific growth rate, weight gain rate, feed conversion ratio, or survival rate ( P > 0.05). However, 60% replacement significantly reduced growth performance and protein deposition while increasing lipid accumulation and impairing muscle texture ( P < 0.05). Integrated omics analyses showed that moderate CPC inclusion enhanced antioxidant capacity and metabolic homeostasis, whereas excessive substitution induced intestinal damage, oxidative stress, and suppressed AKT/4E-BP1 signaling, limiting protein synthesis and triggering metabolic reprogramming. These results indicate that the safe replacement level of CPC in diets for Lateolabrax maculatus should not exceed 45%, providing a theoretical basis for reducing fishmeal usage and improving the utilization of plant protein sources in aquafeeds.