Effects of Mannan Oligosaccharides on Growth, Antioxidant and Immune Performance, and mTOR Signaling Pathway in Juvenile Tilapia ().

Mannan oligosaccharide (MOS), a prebiotic derived from yeast cell walls, has been shown to enhance growth performance and health status in various aquatic species. As an exogenous antigen adjuvant, MOS modulates T-cell-mediated immune responses, thereby improving immune function and suppressing excessive inflammatory reactions. This study aimed to evaluate the effects of dietary MOS supplementation on growth performance, serum biochemical parameters, muscle composition, digestive enzyme activity, antioxidant and immune status, and the mTOR signaling pathway in juvenile GIFT tilapia (). Juveniles (initial body weight: 16.17 ± 1.32 g) were randomly assigned to six treatment groups (three replicate tanks per group) and fed diets supplemented with MOS at 0, 0.2%, 0.4%, 0.6%, 0.8%, and 1% (equivalent to 0, 2, 4, 6, 8, and 10 g/kg of diet, respectively) for 60 days. Compared with the control group, fish fed MOS-supplemented diets exhibited significantly higher ( < 0.05) weight gain rates, specific growth rates, and protein efficiency ratios, along with a significantly lower ( < 0.05) feed conversion ratio. Serum albumin, high-density lipoprotein, and lysozyme levels were significantly increased ( < 0.05), whereas triglycerides, low-density lipoprotein, aspartate aminotransferase, and alanine aminotransferase levels were significantly decreased ( < 0.05). In the liver, head kidney, and spleen, the expression of pro-inflammatory genes (tumor necrosis factor α, interleukin 1β, interleukin 6, interleukin 8, and interferon γ) was significantly downregulated ( < 0.05), while the expression of antioxidant and protective genes (superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, nuclear factor erythroid 2-related factor 2, lysozyme, alkaline phosphatase, interleukin-10, transforming growth factor β, and heat shock protein 70) as well as mTOR signaling pathway-related genes (mammalian target of rapamycin, akt protein kinase B, phosphatidylinositol 3 kinase, and ribosomal protein S6 kinase polypeptide 1) was significantly upregulated ( < 0.05). Overall, MOS positively affects tilapia's growth, health, and immunity, with 0.60% identified as the optimal dietary level based on growth performance.