Functional Benefits of Fermented Sesame Oilcake in the Diet of Nile Tilapia, Oreochromis niloticus: Insights Into Immunity, Oxidative Status, and Gut Microbiota.

This study evaluated the effects of dietary inclusion of fermented sesame oilcake (FSOC) on growth performance, antioxidant responses, immune parameters, bactericidal activity, and gut microbial composition in juvenile Nile tilapia, Oreochromis niloticus. FSOC was produced by aerobic solid-state fermentation using Saccharomyces cerevisiae. Fish (5-month-old, 13.31 ± 0.73 g, all-male) were randomly distributed into three treatment groups and fed diets containing 0% (control [CTL]), 10% (S-10), or 20% (S-20) FSOC for 8 weeks. Growth performance, feed conversion ratio, and survival were not significantly affected by FSOC inclusion (p > 0.05). However, dietary FSOC significantly enhanced several immunological parameters, including lysozyme activity and total immunoglobulin (Ig) levels in plasma, liver, kidney, and skin mucus (p < 0.05). Antioxidant markers such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and reduced glutathione (GSH) were significantly elevated in hepatic and intestinal tissues of FSOC-fed fish, accompanied by a significant reduction in malondialdehyde (MDA) levels (p < 0.05), indicating improved oxidative status. Skin mucus from FSOC-fed tilapia exhibited significantly greater bactericidal activity against Aeromonas hydrophila and Streptococcus iniae. Gut gene expressions showed different patterns in the S-10 and S-20 treatments, as the S-10 treatment showed only an upregulation in tumor necrosis factor-a (tnf-α) expression, while the S-20 treatment showed upregulations in various anti-inflammatory, proinflammatory, antioxidant, and chaperon gene expressions. Additionally, gut microbiota analysis revealed that FSOC supplementation significantly increased the abundance of beneficial microbes (Saccharomyces sp., Lactobacillus sp., and Bacillus sp.) while reducing the presence of opportunistic pathogens (Aeromonas sp., Vibrio sp., and Streptococcus sp.). Overall, these findings suggest that FSOC is a promising functional feed ingredient capable of improving immune competence, oxidative resilience, and gut health in Nile tilapia without compromising growth.