Copper oxide nanoparticles (CuO-NP) are widely studied nanoparticles due to their broad applications in various fields. Nonetheless, little data exists regarding their chronic toxicity to aquatic animals causing aquatic pollution. This study was designed to analyze the toxicological effect of different concentrations of CuO-NPs concentrations on the bighead carp (Hypophthalmichthys nobilis). They were synthesized using co-precipitation method and characterized by X-Ray diffraction, Fourier-transform infrared (FT-IR) and UV-visible spectroscopy that confirmed 32.84nm size, elemental composition and reduction level, respectively. The acute toxicity in terms of 96-h LC₅₀ was determined using bighead carp as a model organism. After acute toxicity testing, DNA damage in blood peripheral erythrocytes of fish was observed by comet assay and oxidative stress in terms of superoxide dismutase (SOD), glutathione S-transferase (GST), catalase (CAT) and lipid peroxidation (LPO) levels were evaluated after chronic exposure of different concentrations (1/3^rd and 1/5^th of 96-hLC₅₀) of CuO-NPs in gills, liver, heart and muscle tissues of bighead carp. Samplings were conducted after exposure periods of 15, 30, and 45 days. The significantly higher damaged nuclei (%) and genetic damage index were observed in bighead carp after 1/3^rd of exposure concentration than 1/5^th of 96h LC₅₀. Significant changes in enzyme activities and LPO level occurred regarding dose and time-dependent manner. The activity of SOD and GST increased for 30 days, followed by the decrease at both experimental doses. CAT activity significantly declined as exposure time was elevated, while the level of LPO also increased in various fish organs as compared to the control group. This study indicates that CuO-NPs have a stronger impact on fish and toxicity increases as exposure time and dose increases.