Abstract
This study examines the efficacy of green-synthesized zinc oxide nanoparticles (ZnO NPs) as an immunostimulant and antibacterial agent in aquaculture. Citrus limetta leaf extract was used for the synthesis of ZnO NPs, which were then studied using UV-Vis spectroscopy, FTIR, XRD, SEM, and zeta potential analysis to confirm their stability, crystalline structure, nanoscale size, and functional surface characteristics. Oreochromis niloticus experienced diets supplemented with ZnO NPs at 0, 0.5, 1.0, and 2.0 mg/kg for 60 days as part of an in vivo investigation. Results revealed that the 1.0 mg/kg dose (Group III) significantly improved innate immune measurements, including lysozyme activity, respiratory burst, and serum protein levels, as well as growth performance and hematological indices. Following a challenge with Aeromonas hydrophila, this group exhibited the highest survival rate (90%), lowest bacterial load in tissues, and minimal histopathological damage, confirming robust disease resistance. Higher doses showed reduced efficacy, indicating an optimal threshold. These findings establish ZnO NPs as a sustainable alternative to antibiotics, effectively enhancing immunity and controlling bacterial diseases in fish farming.