Dietary Effects of Probiotic Bacteria, Bacillus amyloliquefaciens AV5 on Growth, Serum and Mucus Immune Response, Metabolomics, and Lipid Metabolism in Nile Tilapia (Oreochromis niloticus)

In the present study, we investigated the effect of dietary supplementation with the probiotic Bacillus amyloliquefaciens AV5 (OR647358) on the growth, serum and mucus immune responses, metabolomics, and lipid metabolism of Oreochromis niloticus. Fishes (27.2 ± 1.7 g and 9.0 ± 1.2 cm) were fed three distinct meals: a commercial diet (control-GC) and two treatment diets supplemented with probiotics at 10⁶ (G1) and 10⁸ cfu/g (G2), respectively, for 30 days. In the G2 group, the final weight, specific growth rate, weight gain rate, survival rate, and feed conversion ratio of the fish were significantly improved (p < 0.05). Lysozyme, myeloperoxidase, and alkaline phosphatase activities in the mucus of fish were significantly higher (p < 0.05) in the G1 and G2 groups. The serum total protein, superoxide dismutase, glutathione peroxidase, reactive oxygen species, and reactive nitrogen species levels were noticeably higher (p < 0.05) in fish fed G1 and G2. In addition, in the G1 and G2 groups, higher levels of enzymes involved in lipid metabolism, such as pyruvate kinase, 2-hydroxyethyl-ThPP, and dihydrolipoamide dehydrogenase, were increased. Distal gastrointestinal metabolites, such as glycerophospholipids and histidine, were observed. These findings strongly indicate that incorporating B. amyloliquefaciens AV5 at 10⁸ cfu/g into commercial feeds positively influences fish growth, immunity, and lipid metabolism.