Background and purpose: Simultaneous exposure of nanoparticles can cause serious damage to aquatic organisms including fish. The aim of this study was to investigate the toxicity effect of subchronic exposure of copper oxide nanoparticles (CuO NPs) in presence of titanium dioxide nanoparticles (TiO₂ NPs) on the histopathology of gill and kidney tissues of fish model in vivo exposure.

Materials and methods: In this study, one non-lethal concentration of TiO₂ NPs, two non-lethal concentrations of CuO NPs, two concentrations of TiO₂ NPs and CuO NPs mixture, and a control group (no chemicals) were used. After 10 days of exposure to these materials, samples of gill and kidney tissues were collected. In order to study classical histology the samples were prepared by hematoxylin-eosin staining and the slides were photographed by optical microscopy.

Results: The damages caused in gill were as following: secondary curved blades, increased mucus secretion, increase in the agglomeration of secondary lamellae, and aneurism and hyperplasia. Also, blood vessels dilation, vacuoles, necrosis, focal tubule degeneration, and increase in melano-macrophage were observed in kidney tissue of common carp.

Conclusion: The study suggested that toxic effects of CuO NPs on tissues of common carp in the joint presence of TiO₂ NPs were synergistic.