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. ccupsulatus, 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). Expressions of nuclear factor erythmid 2-related factor 2, glutathione peroxide - 1 mRNA and total superoxide dismutase mRNA showed no significantly difference (P > 0.05). However, nuclear factor-kappa B, tumor necrosis factor-a, interfelony, interleukin 8, interleukin 10 and interleukin 16 decreased significantly (P < 0.05). Nonetheless interleukin 113 remained unchanged (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.