Influence of a mixture of oligosaccharides and β-glucan on growth performance, feed efficacy, body composition, biochemical indices, combating Streptococcus iniae infection, and gene expression of Nile tilapia (Oreochromis niloticus)

A 60-feeding day was performed to explore the potential influence of dietary intervention with a mixture of oligosaccharides and β-glucan (OLG) on growth, feed utilization, body composition, biochemical parameters, growth-related genes, and resistance to Streptococcus iniae infection of Nile tilapia (Oreochromis niloticus). Fish (n = 360, average weight 24 ± 0.2 g) were allotted into four experimental groups. Fish were received basal diets and inclusion of a mixture of oligosaccharides and β-glucan (1:1) at various levels 0 (OLG0), 1 (OLG1), 1.5 (OLG1.5), and 2 (OLG2) g/kg feed for 60 days. Fish were erratically scattered into tanks at a density of 30 fish/tank and the experiment was conducted in triplicates. All OLG groups had better final body weight, feed conversation ratio (FCR), and body weight gain and percentages (p < 0.05), while the feed intake did not change (p > 0.05). Fish fed with 1.5 or 2 g of OLG exhibited higher SGR, survival rates, and ADG than the OLG1 and OLG0 groups. All OLG-treated groups significantly improved the fish body composition in dose-dependent manner (p < 0.05). Protein fractions (total protein, albumin, and globulins) were significantly improved, and liver enzymes were significantly decreased (AST, ALT, and ALP) in all-OLG supplemented in dose-dependent manner (p < 0.05). Both OLG1.5 and OLG2 groups had lower values of MDA and higher levels of lysosome activity compared to those in other groups. Fish in the OLG2 group recorded the best results for antioxidant biomarkers GPx, IgM, CAT, and SOD compared to those in other groups. The expressions of GH and IGF-1 genes were significantly up-regulated by dietary inclusion in dose-dependent way (p < 0.05). Fish that fed OLG exhibited higher survival rate against S. iniae infection compared to the control one. Overall, this research suggested a suitable integration level of β-glucan and oligosaccharides that could enhance growth and feed parameters, body composition, blood profile, serum metabolites, growth-associated genes, and resistance to S. iniae infection of Nile tilapia, with an ideal dose of 1.5 and 2 g/kg feed.