Postbiotics enhance immune competence in black rockfish (Sebastes schlegelii): linking innate immunity, apoptosis, and resistance to bacterial infection

Abstract Background This study investigated the functional potential and safety of postbiotics derived from Latilactobacillus curvatus NBL2305 as a dietary feed additive for juvenile black rockfish ( Sebastes schlegelii ). Fish were fed diets supplemented with NBL2305-derived postbiotics, and their effects on growth performance, immune responses, antioxidant capacity, apoptosis-related gene expression, intestinal microbiota, and disease resistance were evaluated. Results Supplementation with postbiotics significantly improved growth performance and feed utilization, as indicated by increased weight gain and specific growth rate, along with a reduced feed conversion ratio. Innate immune responses were enhanced, as demonstrated by elevated activities of myeloperoxidase, superoxide dismutase, and lysozyme together with the upregulated expression of immune-related genes, including il8 , il1b , tnfa , tnfsf13b , and nfkb1 . In addition, postbiotic treatment modulated apoptosis-related gene expression in the liver, characterized by the downregulation of pro-apoptotic genes ( bax , tp53 , and casp3 ) and the upregulation of anti-apoptotic genes ( bcl2 and xiap ), indicating an anti-apoptotic gene expression profile. The postbiotics also exhibited strong antimicrobial activity against major fish pathogens and considerable antioxidant capacity. These functional effects were further supported by an in vivo challenge test, in which the postbiotic-fed group showed significantly higher survival following Edwardsiella tarda infection. No adverse effects were observed in serum biochemical parameters, somatic indices, or histopathological analyses, supporting the short-term safety of supplementation under the experimental conditions evaluated. Moreover, the intestinal microbiota composition remained stable, with selective enrichment of beneficial taxa. Conclusions Collectively, these findings demonstrate that NBL2305-derived postbiotics are safe and effective functional feed additives that enhance growth, modulated innate immune responses, and disease resistance in aquaculture species.