Chenglong Wu

The increasing need for aquafeed protein sources calls for sustainable substitutes for fish meal (FM). Degossypolled cottonseed protein (DCP) represents a promising plant-derived protein, but its impact on the intestinal health of carnivorous fish is not well understood. This study assessed how partial replacing FM with DCP affects growth performance, intestinal barrier integrity, immune function, and antioxidant status in juvenile largemouth bass. Five isonitrogenous and isoenergetic diets were prepared, in which DCP replaced 0%, 20%, 40%, 60%, or 80% of the FM. Following an 8-week feeding period, the group receiving 20% DCP replacement showed no significant differences in growth or feed efficiency relative to the control, while 80% replacement caused marked growth reduction and increased visceral fat accumulation. High replacement levels (≥60%) downregulated antioxidant-related genes, damaged intestinal villi, compromised barrier integrity (mucins and tight junctions), and activated inflammatory responses via the NLRP3 inflammasome pathway, along with suppression of immune parameters. In conclusion, replacing 20% of FM with DCP was safe for largemouth bass, while excessive substitution (≥60%) induces intestinal oxidative stress, barrier dysfunction, inflammation, and immunosuppression. These findings support DCP as a viable partial substitute for FM in commercial diets for this species.

With the rapid expansion of intensive aquaculture, the frequent outbreak of diseases and the overuse of antibiotics have become increasingly critical issues. Therefore, developing green and efficient antibiotic alternatives is essential for the sustainable growth of the industry. As a novel probiotic, Bacillus velezensis has shown great potential in improving the disease resistance of aquatic animals, owing to its excellent spore-forming ability, broad-spectrum antibacterial activity, and immunoregulatory functions. This paper systematically reviews the main mechanisms by which B. velezensis enhances disease resistance in aquatic animals, including directly inhibiting pathogens through the secretion of various lipopeptides and polyketides such as surfactin, iturin, and fengycin; interfering with pathogen quorum sensing systems via quorum quenching enzymes, thereby suppressing virulence factor expression and biofilm formation; modulating intestinal microbiota structure to increase the abundance of beneficial bacteria while reducing pathogenic proliferation; and activating the non-specific immune system of the host to upregulate immune-related indicators such as acid phosphatase, superoxide dismutase, and key cytokines (such as IL-1β, TNF-α). In addition, this review summarizes the application effects of B. velezensis on improving aquaculture water quality and promoting host growth. Furthermore, the potential ecological impacts on natural microbial communities and strain-dependent biosafety risks are evaluated. Finally, current research limitations—such as strain-specific functional differences, insufficient in-depth analysis of mechanisms, and inconsistent application outcomes—are discussed. Future prospects for promoting the efficient and stable application of B. velezensis in aquaculture through strategies including gene editing, multi-omics integration, and precise formulation compounding are also proposed.