Neem <i>Azadirachta indica</i> extract augments serum, mucus innate immunity, antioxidant status, and resistance to <i>Aeromonas hydrophila</i> in Rohu <i>Labeo rohita</i>

Abstract Objective In aquaculture, medicinal plants and their derivatives serve as potent natural boosters for the immune system and effective stress relievers for aquatic organisms. This study explored how neem plant (NP) Azadirachta indica leaves extract influenced the immune system and antioxidant capacity of Rohu Labeo rohita. Methods The sample included 240 healthy Rohu fingerlings, averaging 22.54 ± 0.82 g in weight, divided randomly into four groups, each containing triplicates of 20 fish per glass aquarium. The control group (NP0) received a standard diet without additives, whereas the other groups were fed NP-infused diets at concentrations of 2 g/kg (NP2), 4 g/kg (NP4), and 6 g/kg (NP6) over a 60-d period. After this feeding trial, the fish were exposed to Aeromonas hydrophila to assess their immune response and their survival rates were calculated. Results The findings revealed that relative to the control group, the NP4 group exhibited significantly (P &amp;lt; 0.05) higher levels of lysozyme activity in both serum and mucus. Peroxidase activity in serum was elevated in the NP4 and NP6 groups, although the difference was not statistically significant. However, peroxidase activity in mucus was significantly (P &amp;lt; 0.05) higher in the NP6 group. Additionally, serum levels of immunoglobulin, total protein, and ACH50 were considerably (P &amp;lt; 0.05) higher in the NP6 group, whereas mucus levels of immunoglobulin, protease, and total protein were significantly (P &amp;lt; 0.05) elevated in the NP4 group. Enzymatic activities such as catalase, superoxide dismutase, and glutathione dehydrogenase in serum and fish survival were significantly (P &amp;lt; 0.05) higher in the NP4 group than in the control. The survival rate of the fish was higher in the NP6 group followed by NP4. Conclusions In conclusion, the findings suggest that NP extract holds potential as a natural immunostimulant for Rohu aquaculture.