Common carp (Cyprinus carpio), Prussian carp (Carassius gibelio) and Peppered cory (Corydoras paleatus) were evaluated as target species to perform genotoxicity tests for heavy metals. Fishes were exposed to different doses of cadmium (0.005-0.1 mg/L) and copper (0.01-0.25 mg/L) for 21 days. Hexavalent chromium at a single dose of 5 mg/L was used as a positive control. Frequencies of micronuclei and binuclei were evaluated comparatively in peripheral blood erythrocytes, gill epithelia] cells and liver cells. As a result it was observed that, fish species and their tissues showed differential sensitivity to the heavy metal treatment. In general, frequencies of micronucleated and binucleated cells significantly increased following the exposure for 21 days to copper, cadmium and chromium. On the other hand, gill and liver cells showed higher frequencies of micronuclei and binuclei than erythrocytes. Our results indicated the formation of micronuclei and binuclei in fish cells caused by their exposure to cadmium, copper and chromium, thus verifying results obtained earlier on mammals, which indicated that these heavy metals have cytotoxic and genotoxic effects. The suitability of the micronucleus assay in native fish species for the screening of aquatic genotoxicants is highlighted and the importance of target tissue selection in the piscine micronucleus test is emphasized. (C) 2005 Elsevier Ltd. All rights reserved.