Lactiplantibacillus plantarum O126 postbiotics boost growth, antioxidant levels, disease resistance, and gut health in sea cucumber (Apostichopus japonicus)

Lactiplantibacillus plantarum ( L. plantarum ) postbiotics promote animal health, but their application in Apostichopus japonicus is currently limited. This study added L. plantarum O126 postbiotics to the diet at concentrations of 1‰, 2‰, and 4‰ (w/w) for 42 days to assess their impacts on A. japonicus. The results showed that, in terms of growth performance, the medium-dose (2‰, LPP-M) and high-dose (4‰, LPP-H) groups significantly increased the final body weight and specific growth rate (SGR), and reduced the feed conversion ratio (FCR). Regarding digestion and gut morphology, the LPP-M and LPP-H groups significantly enhanced gut trypsin and lipase activities and increased the height and width of midgut villi. With respect to antioxidant capacity, L. plantarum O126 postbiotics increased T-AOC, CAT, and SOD levels and upregulated the expression of antioxidant-related genes PRDX5 and PRDX6 . In terms of immunoregulation, L. plantarum O126 postbiotics increased ACP and AKP activities and upregulated the expression of immune-related genes Rel , P50 , and C3-2 . Regarding disease resistance, after the Vibrio splendidus challenge, all experimental groups exhibited reduced evisceration rates, with the LPP-M group showing the lowest rate (40%). In terms of gut microbiota, the α-diversity of the experimental groups was significantly increased, with higher levels of beneficial bacteria ( Bacillus , Exiguobacterium , Vagococcus ) observed in the LPP-M and LPP-H groups. Overall, L. plantarum O126 postbiotics improved the growth and disease resistance of A. japonicus by enhancing digestion, antioxidant capacity, immune function, as well as by regulating gut microbiota, with a medium dose (2‰, w/w) showing the best effect.