Abstract
This study investigated the effects of dietary supplementation with Mentha piperita (MP) on growth, immune enhancement, and disease resistance in Nile tilapia (Oreochromis niloticus) over a 90-day period, particularly against Aeromonas hydrophila. MP was incorporated into the diets at concentrations of 0.0%, 0.2%, 0.4%, and 0.6%. Analysis of the essential oil composition of MP identified menthol derivatives as the primary components, along with other bioactive compounds. The results revealed that MP supplementation significantly enhanced growth performance, with fish receiving the 0.6% MP diet achieving the highest weight gain, growth rate, and feed efficiency. Additionally, MP significantly enhanced the fish's resistance to A. hydrophila infection, with the highest survival rate observed in the 0.6% MP group. Further analyses revealed that MP positively influenced blood parameters, improving RBC and WBC counts, hemoglobin levels, as well as serum immunoglobulin M and phagocytic activity. MP also mitigated oxidative stress by increasing antioxidant enzyme activity and reducing malondialdehyde levels. Moreover, MP supplementation at the concentration of 0.6% maintained intestinal integrity against bacterial damage. Gene expression analysis showed that MP upregulated insulin-like growth factor 1, suggesting a potential mechanism for improved growth. Interestingly, MP downregulated the expression of the inflammatory gene nuclear factor kappa B before the bacterial challenge, while its expression remained more downregulated post-challenge compared to control. These findings highlight the potential of MP as an effective feed additive that enhances growth rates in Nile tilapia, boosts immunity against diseases, and improves their overall health.