The Synergic Effect of Gut-Derived Probiotic Bacillus cereus SL1 And Ocimum sanctum on Growth, Intestinal Histopathology, Innate Immunity, and Expression of Enzymatic Antioxidant Genes in Fish, Cirrhinus mrigala (Hamilton, 1822)

An effective alternative approach to combat aquaculture challenges is the strategic application of bioresources, which not only mitigate disease ailment but also optimize fish growth. Hence, current research was undertaken to highlight the synergic role of bioresources such as plant immunostimulant Ocimum sanctum along with potent gut-derived probiotic Bacillus cereus strain SL1 (Gen Bank Accession Number: FJ627945.1) on mrigal (Cirrhinus mrigala) growth, antioxidant status, gut histopathology, and immune response. For 90 days, fingerlings (average weight 6.8 +/- 0.5 g) were fed on diets having varying concentrations of O. sanctum and B. cereus. After the completion of the feeding trial, various growth, immunity, and histological and antioxidant metrics were evaluated according to standard procedures. In comparison to the control and other treatment groups, T3 group showed a significant (P < 0.05) increase in growth parameters, antioxidant enzymatic activity, and hematological and immunological parameters. In addition to it, supplementation of both B. cereus and O. sanctum also upregulated the antioxidant-related gene expressions, such as hepatic catalase gene by 1.89-3.00 folds, hepatic SOD-1 by 4.46-7.52 folds, and GPx-1of the liver by 1.56-1.95 folds. For 10 days, fingerlings were challenged with the pathogenic bacterium Aeromonas hydrophila (MTCC-1739), and maximum survival rate (77.77%) was reported in fingerlings of T3 treatment. Further histopathological studies of gut tissues affirm that O. sanctum and B. cereus play a synergic role in the protection of digestive organs from the pathogenic bacterium A. hydrophila. These results suggest that O. sanctum and B. cereus synergically improved the growth performance, immunity, antioxidant status, and gut histology of C. mrigala leading to its sustainable culture.