Effects of dietary supplementation with Bacillus subtilis on immune, antioxidant, and histopathological parameters of Carassius auratus gibelio juveniles exposed to acute saline-alkaline conditions.

Salinity and alkalinity are important indicators of the aquatic environment, and saline-alkali stress has negative effects on aquatic organisms. Dietary supplementation with probiotics can improve the overall health and productivity of aquatic animals. Bacillus subtilis is a widely used probiotic in aquaculture. A total of 240 Carassius auratus gibelio (13.85 ± 0.15 g) were assigned to four groups. This experiment used a completely randomized design with three replicates and a 2 × 2 factorial scheme, with two saline-alkali concentrations (0 g/L NaCl + 0 g/L NaHCO3 and 5 g/L NaCl + 2.52 g/L NaHCO3) and two diets (control and supplemented with 108 CFU/g B. subtilis). After 12, 24, 48, 72, and 96 h of saline-alkali exposure, fish blood samples were collected and serum levels of immunoglobulin M, alkaline phosphatase, and acid phosphatase were measured. Gills and kidneys were sampled to analyze superoxide dismutase activity, catalase activity, malondialdehyde content, and histopathological alterations. The results suggested that a B. subtilis-supplemented diet may enhance immunity, improve antioxidant ability, and reduce tissue damage in C. gibelio exposed to saline-alkali stress. [ABSTRACT FROM AUTHOR]