Effects of dietary supplementation with Bacillus velezensis on the growth performance, body composition, antioxidant, immune-related gene expression, and histology of Pacific white shrimp, Litopenaeus vannamei

In recent decades, probiotics have become an acceptable aquaculture strategy for shrimp growth promotion and immune modulation. This study aimed to evaluate the effect of Bacillus velezensis on Litopenaeus vannamei following a 60-day trial. L. vannamei (3 ± 0.4 g) were distributed into four groups with three replicates per group and fed an isonitrogenous diet supplemented with B. velezensis at 0, 1 × 10⁷, 1 × 10⁸, and 1 × 10⁹ CFU/g, which were defined as the control, G1, G2, and G3 groups, respectively. B. velezensis significantly improved the growth, survival rate, and proximate body composition of L. vannamei (P < 0.05). All groups fed the B. velezensis diet showed significant increases in digestive enzymes (lipase, amylase, and protease), superoxide dismutase (SOD; G3), catalase (CAT; G3, G2, and G1), lysozyme activity (G3 and G2), immunoglobulin M (IgM), bactericidal activity BA%, alkaline phosphatase (AKP), and acid phosphatase (ACP) compared with the control group (P < 0.05). Malondialdehyde (MDA), triglycerides, cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels were significantly decreased in all groups fed B. velezensis diet compared with the control group (P < 0.05). The expression levels of SOD (G3), LZM, and serine proteinase genes were significantly higher in L. vannamei fed diets containing B. velezensis than in the control group (P < 0.05). This is the first study to address the effects of B. velezensis on the expression of the LZM and serine proteinase genes in L. vannamei. L. vannamei fed diet containing B. velezensis had more B and R cells in its hepatopancreas than did the control group. In conclusion, B. velezensis is a promising probiotic that can be safely added to the diet of L. vannamei with 1 × 10⁹ CFU/g. Its application had a positive influence on the health status, survival rate, nutritional value, and immunity of L. vannamei.