The increasing commercial applications of copper oxide nanoparticles (nCuO) have raised concerns about the risk to the aquatic environment. The purpose of this study was to examine the toxicity of low concentrations of nCuO and Cu(II) as copper sulfate in juvenile rainbow trout. Juveniles were exposed to a range of concentrations of nCuO (12.8, 32, 80, 200 and 500 µg/L as total Cu) and Cu(II) (12.8, 32 and 80 µg/L total Cu) for 96 h at 15 °C under constant aeration. After the exposure period, fish were removed and examined for total and labile Cu in gills, oxidative stress (lipid peroxidation and glutathione S-transferase), genotoxicity (DNA damage), and reticulum endoplasmic stress (heat shock proteins 70 and protein-ubiquitin levels). The data revealed that although nCuO did not lead to the increase in Cu accumulation in fish, the nanoparticles produced changes that were not observed with Cu(II) such as increased glutathione S-tranferase activity in gills with a strong decrease in lipid peroxidation and DNA strand breaks in the same tissues. Labile Cu levels in gills were increased and decreased by nCuO and Cu(II), respectively. Both forms of Cu were able to elicit changes in heat shock proteins and protein-ubiquitinylation. In conclusion, exposure to low concentrations of nCuO could produce change in gills and the liver in fish before the accumulation of Cu loading in tissues. The effects of nCuO differ from those of Cu(II) in rainbow trout.
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