Potential effects of dietary fermented Sargassum muticum on growth performance, intestinal health, immune-antioxidant related gene responses, and resistance to bacterial infection in Nile tilapia.

Recently, fermented brown algae have gained interest as a food source due to their high functionality and numerous bioactive components. Therefore, the current study used Lactobacillus plantarum and Saccharomyces cerevisiae probiotics to examine the possible effects of dietary fermented Sargassum muticum (DFSM) on the growth performance of Nile tilapia (Oreochromis niloticus), intestinal health, blood indices, antioxidant levels, and immune response. For 60 days, Nile tilapia (15 fish/aquarium) with an average weight (21.59 ± 1.06 g, four replicates) were fed five isonitrogenous diets that contained 0.0 % (control), 0.5 %, 1 %, 2 %, and 3 % DFSM. The bacterial Aeromonas hydrophila strain was injected intraperitoneally into fish of each treatment following the feeding trial. All growth indices in Nile tilapia were significantly enhanced with a DFSM inclusion above 0.5 %, compared to the control diet. The results displayed that the DFSM in the diet improved fish intestinal health and blood indices, especially in fish fed a diet containing 2 and 3 DFSM %. The fish fed the DFSM displayed a reduced MDA value compared to the control diet and a rise in immunological indices (phagocytic activity and lysozyme) and antioxidants (SOD and CAT), especially at 2 and 3 DFSM % diet. Fish fed 2 and 3 % DFSM diet had significantly upregulated the genes CAT, SOD, GPx, and Nrf2 expression compared to the diet 0.5,1 % and control groups. Conversely, IL-8, IL-1β, and TNF gene expression were upregulated in the control one and downregulated in fish fed a diet containing 2 and 3 DFSM %. The histological analysis revealed that all tissues examined in fish fed DFSM exhibited intact structural improvements as the amount of DFSM supplementation increased. Fish groups fed a diet containing 2 and 3 DFSM % diet exhibited higher survival rates after an A. hydrophila infection challenge than the control group. The study concluded that Nile tilapia requires a 2.5 to 3.0 DFSM% diet to boost growth performance, health status, and infection resistance.