Radioactive wastes may be leached into freshwater, either accidentally or in industrial effluents. We have studied gamma radiation-induced DNA damage in the freshwater  fish Cyprinus carpio. Fish were irradiated with 2–10 Gy gamma radiation and genotoxic effects in blood cells were studied with  the micronucleus (MN) and comet assays. Micronuclei and a dose-dependent increase in comet-tail DNA were seen in dose- and time-dependent studies. The highest % tail DNA was observed at 24 h, declining until 72 h, which may indicate the repair of radiation-induced DNA single-strand breaks after gamma radiation. However, double-stranded DNA damage may not have been repaired,  as indicated by increased micronuclei at later periods. A positive correlation was observed between the comet and micronucleus assay results. This study confirms the mutagenic/genotoxic potential of gamma radiation in the Common carp, as well as the possible combined use of the micronucleus and comet assays for in vivo  laboratory studies with fresh-water fish for screening the genotoxic potential of radioactive pollution.