The killifish Nothobranchius rachowi, a new animal in genetic toxicology.

Nothobranchius rachowi, a tropical fish that belongs to the family of the Cyprinodontidae, is introduced as a new animal for genetic toxicological studies. The karyotype of N. rachowi consists of 16 large chromosomes. This species can be used for studies on chromosomal aberrations as well as for observations on sister-chromatid exchanges (SCEs). Exposure to 120 mg ethyl methanesulphonate per litre water induced 0.66 SCEs per chromosome, whereas the spontaneous frequency amounted to 0.10 SCEs per chromosome. A comparative study with Umbra pygmaea indicated that the sensitivity for this kind of mutagen is the same in both species. After exposure of N. rachowi to 50 mg cyclophosphamide per litre of water, 0.35 SCEs per chromosome were induced, showing that promutagens could be detected. It is postulated that N. rachowi can be used for screening both pure compounds and surface water for genotoxic potential. An advantage of N. rachowi over Umbra spp. is that the former species is more likely to breed under laboratory conditions.