Muscle Quality Responses of Pearl Gentian Grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) to Fishmeal Replacement by Defatted Silkworm Pupae Meal: Insights from Texture, Histology, Antioxidant Status and Metabolomics

This study investigated how defatted silkworm pupae meal (DSPM) modulates flesh quality in pearl gentian grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). A total of 360 size-uniform fish were randomly assigned to four dietary treatments for 8 weeks: D0, the fishmeal (FM) based control diet; and D1, D2, and D3, in which DSPM substituted 25%, 50%, and 100% of dietary FM, respectively, with three replicates per treatment and 30 fish per replicate. Compared with D0, D1 and D2 improved final body weight, weight gain rate, specific growth rate, and feed conversion ratio, whereas D3 reduced survival and feed utilization. For flesh quality, D2 showed the most favorable phenotype, characterized by higher crude protein, collagen, flavor-associated amino acids, pH, texture attributes, and muscle fiber density, together with lower ether extract, cooking loss, freezing loss, and shear force. DSPM substitution also increased unsaturated and polyunsaturated fatty acid proportions and improved lipid health indices. Moderate substitution, especially D2, enhanced oxidative stability by increasing SOD and CAT activities and reducing MDA accumulation. Non-targeted metabolomics combined with qPCR analysis of selected flesh quality-related genes suggested that these improvements were associated with osmotic regulation, collagen remodeling, purine metabolism, membrane lipid homeostasis, nutrient sensing, myogenesis, and antioxidant defense. Complete FM substitution impaired muscle structure, water retention, and redox balance. Thus, 50% FM substitution with DSPM effectively optimized grouper flesh quality in this study.