Methanotroph (Methylococcus capsulatus, Bath) as an alternative protein source for genetically improved farmed tilapia (GIFT: Oreochromis niloticus) and its effect on antioxidants and immune response

The aim was to evaluate the effects of increasing bacterial protein meal (BPM) (M. capsulatus, Bath) as a fishmeal replacer in the diets of GIFT. A total of 540 juveniles (initial weight 3 g) were allocated randomly to 18 outdoor floating cages (1 m 1 m 1 m) at 30 fish/cage for 56 days with diets (0, 17, 34, 51, 68 and 85 g/kg) prepared in triplicate. Weight gain rate, specific growth rate, feed intake, feed conversation ratio, and survival rate were not significantly affected across all diets (P > 0.05). Immunoglobulin M and albumin were significantly increased with an increase in BPM, while alanine transaminases, aspartate transaminases, and alkaline phosphatase showed no significant difference (P > 0.05). The activities of catalase, superoxide dismutase, glutathione peroxidase and glutathione showed no significant difference (P > 0.05). Meanwhile, total antioxidant capacity increased significantly, while malondialdehyde showed an opposite trend (P 0.05). However, nuclear factor-kappa B, tumor necrosis factor-α, interfelony, interleukin 8, interleukin 10 and interleukin 16 decreased significantly (P 0.05). In conclusion, our study has demonstrated that M. capsulatus Bath could improve the immune response without affecting the growth and antioxidant capacity in GIFT juveniles