Orange peel meal as a functional feed supplement mitigates heavy metal effects and enhances growth performance, immunity and antioxidant status in Nile tilapia (Oreochromis niloticus) fingerlings reared in heavy metal-polluted water

Abstract

This investigation assessed the efficacy of dietary orange peel meal (OPM) as an efficient feed supplement to mitigate the adverse impacts of heavy metals, enhance growth performance, immunity, and antioxidant status in Nile tilapia ( Oreochromis niloticus ) fingerlings reared in heavy metal-polluted water. Nile tilapia fingerlings were exposed to heavy metal-polluted water and given feed enhanced with variable levels of OPM (2.5, 5, and 10 g/kg feed) for a 100-day period. A control group received a diet without OPM. Dietary OPM addition substantially enhanced the final weight and weight gain of O. niloticus , with the highest improvements observed at 10 g/kg. This concentration also led to the peak daily weight gain and specific growth rate, and the finest feed conversion ratio, indicating a dose-dependent improvement in growth efficiency. OPM significantly reduced the absorption and accumulation of various heavy metals (iron, zinc, copper, cadmium, and lead) in both the liver and gills of tilapia, demonstrating a dose-dependent protecting impact contrary to heavy metal poisonousness. OPM supplementation significantly enhanced immune parameters, including immunoglobulin M (IgM) concentrations, lysozyme activity, phagocytic activity, and phagocytic index, all showing dose-dependent increases, particularly at higher OPM concentrations. OPM consistently resulted in beneficial changes across several blood parameters. It led to significant dose-dependent reductions in triglyceride, cholesterol, AST, ALT, urea, creatinine, and glucose levels, with the 10 g/kg treatment displaying the lowest values for most of these indicators. Dietary OPM positively influenced the oxidative status in both liver and gills. It significantly reduced lipid peroxidation (MDA levels) and increased the antioxidant enzymes such as SOD and CAT in a way that depends on dosage across all tested concentrations, particularly at higher doses. This research concludes that dietary supplementation with orange peel meal effectively mitigates heavy metal effects, enhances growth rate, and improves the status of immunity and antioxidants in O. niloticus fingerlings. These results recommend that OPM can assist as a valuable, efficient feed additive in aquaculture, particularly in environments susceptible to heavy metal pollution, thereby improving fish health and resilience. • Dietary orange peel meal (OPM) effectively mitigated heavy metal-triggered stress in O. niloticus and substantially improved growth rate, feed efficiency. • OPM boosted innate immunity, and antioxidant status, particularly at 10 g/kg inclusion. • OPM reduced oxidative damage, improved liver and kidney function, and lowered heavy metal accumulation in hepatic and gill tissues. • OPM as a sustainable and economical functional feed supplement for tilapia culture in heavy metal–polluted environments.