Influence of brahmi (Bacopa monnieri) dietary supplementation on Nile Tilapia (Oreochromis niloticus) innate immunity, haematology and resistance to Aeromonas hydrophila infection

Nile tilapia (Oreochromis niloticus) is a prominent and widely farmed freshwater finfish species across the globe, accounting for approximately 7.9% of the total global finfish production. However, the unregulated and excessive use of antibiotics in aquaculture has resulted in the emergence of drug-resistant fish pathogens, causing significant production losses. Hence, more increasingly, medicinal plants are being used in the feed formulation of feed of fins fish and shell fish as an alternative to chemotherapeutic agents for strengthening their immune system to prevent the outbreak of fish diseases. In this regard, the current investigation aimed to evaluate the impact of Brahmi (Bacopa monnieri) inclusion in the diet on the hematological profile, non-specific immune response and disease resistance of Nile tilapia (Oreochromis niloticus) against Aeromonas hydrophila infection. A basal feed containing 30% protein was used for all treatments, with Brahmi incorporated at concentrations of 0.5% (T1), 1.0% (T2) and 2.0% (T3), along with a control group (T0) that received no supplementation. All treatments were conducted in triplicates. Following the pathogenic challenge with A. hydrophila, a significant decline was observed in RBC count, platelet count, hemoglobin concentration, MCV, MCH and MCHC values across all groups, including the control, when compared to pre-challenge levels. This reduction is likely attributed to internal hemorrhaging and hemolysis induced by the bacterial infection. Following the pathogenic challenge, the detrimental effects of Aeromonas hydrophila were notably mitigated, indicating a protective role of Brahmi supplementation. Among the treatment groups, T3 exhibited significantly elevated serum lysozyme activity (1.02 ± 0.05 µg/ml; p<0.05) compared to the control and other treatments post-challenge with A. hydrophila. Prior to the challenge, no significant differences (p<0.05) were observed in superoxide anion production among the control and treated groups. However, post-challenge, T3 recorded a significantly higher superoxide anion level (0.27 ± 0.03 U/ml), outperforming the other treatments and control. The challenge trial further revealed that relative percent survival (RPS) was highest in T3 (100%), followed by T1 (80%) and T2 (70%). The improved survival rates observed in the treatment groups can be primarily attributed to the immunomodulatory effect of the herbal supplement Brahmi (Bacopa monnieri), particularly when incorporated at 2% concentration in the diet, enhancing the non-specific immune defense of Oreochromis niloticus against A. hydrophila infection.