Antagonistic effects of nano-copper on lead toxicity in Nile and blue Tilapia: Evidence from growth, immunity, and gene expression

This study investigated the antagonistic effects of dietary nano-copper (Nano-Cu) against lead (Pb) toxicity in two tilapia species, Oreochromis niloticus (n = 360; 55.33 ± 0.54 g) and Oreochromis aureus (n = 360; 55.54 ± 0.61 g), over a 60-day feeding trial. The two tilapia species were divided into four dietary groups: control, Pb (100 µg/kg diet), Nano-Cu (2 mg/kg diet), and Pb+Nano-Cu. Growth performance, digestive enzyme activity, muscle Pb accumulation, serum biochemistry, immune responses, hepatic antioxidant status, and gene expression were assessed, along with histopathological examinations of the intestine and liver. Pb exposure significantly reduced growth indicators, digestive enzyme activities, antioxidant capacity, and immune function, while increasing hepatic malondialdehyde (MDA), serum glucose, liver enzymes, and pro-inflammatory gene expression. Histologically, Pb exposure caused evident structural damage, including villus atrophy in the intestine and hepatic vacuolation with sinusoidal dilatation. In contrast, Nano-Cu supplementation markedly improved growth, protein metabolism, enzymatic activities, and antioxidant status, and mitigated Pb accumulation and toxicity. Nano-Cu preserved normal intestinal and hepatic histoarchitecture and partially alleviated the Pb-induced tissue damage when co-administered. No significant species-specific differences or treatment × species interactions were observed for most variables. These findings demonstrate that Nano-Cu supplementation effectively counteracts Pb-induced toxicity in tilapia and enhances fish health by improving physiological function and maintaining tissue integrity. Future research should expand immunological profiling to include specific immune proteins (e.g., complement C3, IgM) and cytokines (e.g., TNF-α, IL-10), providing deeper mechanistic insight into Nano-Cu-mediated immune modulation under toxic stress, and further investigate its long-term effects under various environmental conditions.