Effects of dietary inclusion of Bacillus amyloliquefaciens AV5 on growth performance, antioxidant activity, innate immune, and hematological responses in Nile tilapia (Oreochromis niloticus) reared at low and high stocking densities

This research work investigated the efficacy of Bacillus amyloliquefaciens AV5 in mitigating the stress effects of stocking densities in Nile tilapia (Oreochromis niloticus). 520 healthy Nile tilapia fingerlings (24.43 ± 1.4g) were randomly allocated to 16 plastic tanks, each with a capacity of 400L. Two stocking densities were tested: low density (37.5 fish/m³) and high density (125 fish/m³) with four treatment groups(low density with a control diet (LDC), high density with a control diet (HDC), low density with a supplemented diet (LDS), and high density with a supplemented diet (HDS)) for 8 weeks. HDC exhibited lower values (P < 0.05) for specific growth rate, final weight, weight gain rate, and specific growth rate than fish fed at LDC, LDS, and HDS. The lowest feed conversion ratio was recorded at the LDS and HDS. There were no significant differences (P > 0.05) in survival rates among treatments. There were no notable disparities (P > 0.05) in the LDC, LDS, and HDS body composition. Antioxidant enzyme activities were greater in LDC, LDS, and HDS than in HDC, while malondialdehyde levels were higher in HDC, and hematology parameters in HDS were improved compared to HDC. Elevated levels (P < 0.05) of phagocytic and lysozyme activity were seen in LDS and HDS. There was no change in glucose levels in HDS and LDC. Nonetheless, cortisol was elevated in HDC compared to LDC, LDS, and HDS. Hence, B. amyloliquefaciens AV5(1 × 10⁸ cfu/g) is a potential probiotic to alleviate HDC-induced stress in O. niloticus.