Development of genotoxicity assay systems that use aquatic organisms.

Our aim is to develop and evaluate monitoring systems that use aquatic organisms to assess the genotoxicity of water in the field and in the laboratory. In a field study, we have shown that the micronucleus assay is applicable to freshwater and marine fishes and that gill cells are more sensitive than hematopoietic cells to micronucleus-inducing agents. Gill cells from Carassius sp. (Funa) and Zacco platypus (Oikawa) collected upstream on the Tomio River (Nara, Japan), tended to have lower micronucleus frequencies than gill cells from fish collected at the midstream of the river. Leiognathus nuchalis (Hiiragi) and Ditrema temmincki (Umitanago), small marine fishes collected periodically at Mochimune Harbor (Shizuoka, Japan), showed seasonal differences in the frequencies of micronucleated gill cells and erythrocytes; they were highest in summer. For laboratory studies, we developed a method for analyzing chromosomal aberrations and micronuclei using Rhodeus ocellatus ocellatus (rose bitterling) embryos. One day after artificial insemination (gastrula stage), we observed structural chromosomal aberrations and micronuclei in the cells of embryos grown in water containing trichloroethylene. Although more work is needed to fully assess their sensitivity, these assays show promise as a means of detecting environmental genotoxins.