[en] Full text: There are few reports on the comparative effects of ionising radiation on different species. Published data report the use of radiation levels far in excess of what could be considered in an environmental context and are therefore difficult to assimilate into environmental research. We are engaged in a comparative study of the cellular effects of non-lethal radiation doses on tissue explants from fish and aquatic invertebrates. The aim of the present work is to investigate the ultrastructural effects of ionising radiation on primary cultures of skin from the rainbow trout. Primary cultures were grown using tissue explants from rainbow trout skin. The cultures were irradiated with doses of cobalt 60 gamma radiation ranging from 0.5Gy to 15Gy. The cultures were fixed in glutaraldehyde, at 7 days post irradiation. They were then post-fixed in osmium tetroxide and dehydrated in ascending grades of alcohol before being embedded in Epon. Blocks of tissue were then sectioned at 1 μm, stained with toluidine blue and surveyed using light microscopy. Ultra-thin sections of particular areas were cut at 50nm and examined by electron microscopy. Nuclear aberrations and changes in cytoplasmic organelles particularly mitochondria, were observed in irradiated skin cultures. Mitochondria were also of a different shape in irradiated cultures. The occurrence of apoptotic bodies in the irradiated cultures suggests that of controlled cell death is involved in the cellular response to radiation. These results may have important considerations for environmental protection. (author)