Postbiotics Derived from Cetobacterium somerae Increase growth, Gut health, and Disease Resistance in Turbot (Scophthalmus Maximus L.).

Postbiotics are gaining recognition as effective components in functional aquafeeds. In this study, we assessed the physiological effects of postbiotics derived from Cetobacterium somerae WT-1 on juvenile turbot (Scophthalmus maximus L.), with a focus on growth performance, intestinal health, and disease resistance. Six experimental diets were formulated to include increasing levels of postbiotics (0%, 0.2%, 0.4%, 0.6%, 1%, and 2%), labeled Ctrl, F-2, F-4, F-6, F-10, and F-20, respectively. Juvenile fish with an average initial body weight of 10.48 ± 0.02 g were fed the test diets over an eight-week period. Notably, fish receiving 0.4% (F-4) and 0.6% (F-6) supplementation presented significant improvements in weight gain, higher digestive enzyme activities (lipase and trypsin), and better feed utilization compared with the control. Histological examination and gene expression analysis further revealed strengthened intestinal barrier structures and enhanced intestinal immune responses in the F-4 and F-6 groups. Additionally, supplementation with postbiotics from C. somerae WT-1 clearly reshaped the gut microbiota, characterized by enrichment of Lactobacillus spp. and increased microbial functional pathways related to amino acid metabolism, vitamin biosynthesis, and xenobiotic degradation in the F-6 and F-4 groups. Notably, the F-4 and F-6 groups also exhibited markedly enhanced kidney innate immune responses, with the upregulation of hif-1α, il-1β, tnf-α, and lysozyme, leading to significantly higher survival rates of turbot following Edwardsiella tarda (E. tarda) challenge. Collectively, these findings demonstrate that C. somerae WT-1-derived postbiotics exert beneficial effects on growth, gut health, and disease resistance in turbot, underscoring their strong potential as functional feed additives in aquaculture.