Use of the mudminnow, Umbra sp., in an in vivo sister chromatid exchange test.

Elevated frequencies of sister chromatid exchange (SCE) have been observed in the chromosomes of mammals and birds as a result of exposure to mutagenic carcinogens. More recently, this phenomenon has been demonstrated in the chromosomes of fishes exposed to genotoxicants. A short-term screening system for mutagenic carcinogens with the use of the mudminnow, Umbra sp., has been developed with SCE as the indicator of genetic damage. This genus of fish possesses a small number (2n = 22) of large chromosomes enabling easy and rapid quantitation of cytogenetic damage. When mudminnows were exposed by ip injection or in situ by the aquatic environment to either direct- or indirect-acting mutagens, dose-dependent increases in SCE were observed. In addition to screening capabilities, the mudminnow system has had application as a biological monitor for genotoxicants in contaminated water systems. The increasing use of the mudminnow SCE system illustrates a renewed interest in the utilization of fishes in mutagenicity and carcinogenicity testing.