The aim of the present study was to investigate the effect of copper oxide nanoparticles (CuO-NPs) and copper ions (Cu++) on guppy (Poecilia reticulata), in order to assess Cu uptake in the gill, and histopathology of gill and intestinal organs in semi-static regimes for 10 days. Guppy fish were assigned into three groups; one control group, and two experimental groups receiving 20 µg/l of either Cu++ or CuO-NPs in a semi-static aqueous culture for 10 days. Gill and intestinal tissue samples were obtained under a standard protocol for further histopathological examinations. The notable alterations observed in gill tissues in the experimental groups were aneurism, fusion, gill epithelial hyperplasia, increased mucous secretion, and necrosis. Noticeable anomalies in intestinal tissue were increase in the number of goblet cells, swelling of goblet cells, degeneration, vacuolation, necrosis, and erosion. Moreover, copper accumulation in gill tissue in the Cu++ treated group was higher than that in the CuO-NPs treated group. In contrast, the severity of histopathological damages in gill and intestinal tissues was greater in the CuO-NPs experimental group.
