Aquatic animals have benefited from Bacillus subtilis-based probiotics over the past few decades. This study evaluated the effects of B. subtilis DSM 32315 probiotics as a feed additive on growth, immune response and resistance to acute ammonia challenge in Nile tilapia. Specifically, four supplemental levels (0%, 0.1%, 0.2%, and 0.3%) of B. subtilis probiotics were tested under two dietary protein levels (32% and 28%). Five replicate tanks were randomly allotted to each dietary treatment, with each tank containing 30 Nile tilapia. After 8 weeks of feeding, Nile tilapia in each tank were exposed to 43.61 mg/L of total ammonia nitrogen for 48 h. The results revealed that reducing protein levels from 32% to 28% did not affect growth performance or antioxidant capacity. However, the low protein diet tended to induce an inflammatory effect shown by increased expressions of TGF-β and IFN-γ genes (P < 0.05) in the liver. The impact was alleviated by the probiotic supplementation. Compared with the non-supplemented group, 0.1% probiotic supplementation remarkably increased plasma lysozyme activity, total antioxidant capacity and complement C3 and interleukin-10 mRNA levels (P < 0.05) in the 28% protein diet, while higher supplementation of probiotics (0.3%) was shown to be beneficial for the high protein diet (32%). In both the dietary protein levels, 0.1% supplementation of probiotics promoted the antioxidant capacity of Nile tilapia before exposure to ammonia stress but higher probiotic supplementation (0.3%) proved to be necessary under ammonia stress as evidenced by higher fish survival rate. Results exhibited that supplementation with B. subtilis probiotics had a better effect on the intestinal morphology (villi height and width) regardless of protein levels. In conclusion, dietary supplementation of B. subtilis DSM 32315 probiotics at 0.1% in the low protein diet and up to 0.3% in the high protein diet showed beneficial effects on the growth, immunity, and antioxidant capacity of Nile tilapia. Under ammonia stress conditions, the higher supplementation of B. subtilis DSM 32315 probiotics at 0.3% improves stress tolerance of Nile tilapia despite the two dietary protein levels (32%; 28%).

在过去的几十年里，水生动物受益于基于枯草芽孢杆菌的益生菌。本研究评估了枯草芽孢杆菌DSM 32315 益生菌作为饲料添加剂对尼罗罗非鱼生长、免疫反应和对急性氨挑战的抵抗力的影响。具体来说，在两种膳食蛋白质水平（32% 和 28%）下测试了四种补充水平（0%、0.1%、0.2% 和 0.3%）的枯草芽孢杆菌益生菌。每个饲料处理随机分配 5 个重复池，每个池包含 30 尾尼罗罗非鱼。饲养8周后，各池内的尼罗罗非鱼暴露于43.61 mg/L的总氨氮中48 h。结果显示，将蛋白质水平从 32% 降低至 28% 不会影响生长性能或抗氧化能力。然而，低蛋白饮食往往会诱发炎症效应，表现为 肝脏中TGF-β和IFN-γ基因表达增加（P < 0.05）。补充益生菌减轻了这种影响。与未补充组相比，28%蛋白质饮食中补充0.1%益生菌显着提高血浆溶菌酶活性、总抗氧化能力以及补体C3和白细胞介素10 mRNA水平（P < 0.05），而益生菌补充量较高（0.3  % ））被证明对高蛋白饮食有益（32%）。在两种膳食蛋白质水平中，0.1% 的益生菌补充量可提高尼罗罗非鱼在氨胁迫之前的抗氧化能力，但在氨胁迫下补充更高的益生菌 (0.3%) 是必要的，鱼的成活率更高就证明了这一点。结果表明，无论蛋白质水平如何，补充枯草芽孢杆菌益生菌对肠道形态（绒毛高度和宽度）都有更好的影响。总之，在低蛋白日粮中添加 0.1% 的枯草芽孢杆菌 DSM 32315 益生菌，在高蛋白日粮中添加高达 0.3% 的枯草芽孢杆菌 DSM 32315 益生菌，对尼罗罗非鱼的生长、免疫力和抗氧化能力产生了有益的影响。在氨胁迫条件下，尽管存在两种日粮蛋白质水平（32%；28%），但添加 0.3% 的更高浓度的枯草芽孢杆菌 DSM 32315 益生菌可提高尼罗罗非鱼的胁迫耐受性。