Dietary acidifiers blend modulates growth, antioxidant, immunity, cytokine performances, and the disease control in Nile tilapia fingerlings fed on high-soybean feeds

The present research examined the use of a commercial acidifier blend (CAB) as a feed supplement on growth, digestive enzymes, antioxidant, immunological biomarkers, and defense of Nile tilapia (Oreochromis niloticus) against Aeromonas sobria disease. Fish (22.7 ± 0.76 g) were fed on 0.0 (the control), 1.0, 2.0, 4.0, or 8.0 g CAB/kg feed for 60 days. After that, fish were intraperitoneally injected with A. sobria, and their survival was monitored for a further 10 days. The fish group that received 4.0 g CAB/kg feed showed the highest growth rate. The improved growth in this group is correlated with the upregulation of mRNA expressions of growth-related genes (IGF-1 and GH). In addition, the highest activities of intestinal proteases, lipase, and α-amylase were observed in fish fed with 4.0 g CAB/kg feed. Compared to the control group, fish fed on CAB-containing diets showed significantly higher activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx). In a parallel way, the mRNA expression of SOD, CAT, and GPx genes were upregulated in CAB-fed groups, particularly at levels of 4.0-8.0 g CAB/kg feed. Conversely, malondialdehyde levels were maximized in the control group but were reduced in CAB-fed fish. Additionally, dietary CAB, especially at levels of 4-8 g/kg diet progressively enhanced the immune function and upregulated the expression of IL-1ß, IL-8, and IL-10 genes. The bactericidal and challenge tests against A. sobria evoked that CAB exhibited antibacterial properties; the maximum mortality rate following the bacterial infection was noted in the control group (90%); meanwhile, CAB-fed fish, especially at a rate of 4.0-8.0 g/kg feed exhibited lower mortality rates (40% and 45%, respectively). Overall, this study recommends incorporating 4.0 g CAB/kg feed to mitigate the negative impacts of dietary soybean and improve the growth, antioxidant, and immunological indices in Nile tilapia fingerlings.