Toxicological impact of copper nanoparticles on rainbow trout: hematological, biochemical, antioxidant, and histopathological responses with oxidative gene expression.

Copper nanoparticles (CuNPs) are increasingly used across various industries due to their catalytic, antimicrobial, and electrical properties. However, their potential toxicity in aquatic environments, particularly to non-target organisms like fish, remains poorly understood. This study investigated the effects of CuNP exposure on rainbow trout (Oncorhynchus mykiss) by comprehensively evaluating hematological, biochemical, antioxidant, molecular, and histopathological parameters. Rainbow trout fingerlings were exposed to varying concentrations of CuNPs (0.2 mg/L, 0.6 mg/L, and 1.0 mg/L) for 7, 14, and 21 days. The results revealed significant dose-dependent declines in hemoglobin (Hb) and red blood cell (RBC) counts, alongside increases in white blood cell (WBC) counts, indicating an immune response to CuNPs-induced stress. Serum biochemistry showed disruptions in albumin, globulin, cholesterol, and triglycerides, suggesting impaired liver function and altered lipid metabolism. Antioxidant enzyme activity, including catalase (CAT), increased significantly, reflecting oxidative stress, while lipid peroxidation (LPO) levels unexpectedly decreased, suggesting possible activation of compensatory mechanisms. Histopathological analysis confirmed severe gill and liver damage, including hypertrophy, hyperplasia, lamellar fusion, necrosis, and cellular degeneration. Molecular analysis showed upregulation of oxidative and, inflammatory genes, and signs of apoptosis. These findings underscore the toxic potential of CuNPs in aquatic environments and highlight the need for careful regulation and environmental monitoring to mitigate their impact.