Umbra limi: a model for the study of chromosome aberrations in fishes

Due to the lack of information available on the effect of various clastogenic agents on the chromosomes of fishes, an in vivo cytogenetics model system was developed. The central mudminnow, Umbra limi, was chosen fro this study because of its ideal karyotype consisting of 22 large meta- and submetacentric chromosomes. Various organs of the fish were investigated to determine their suitability for chromosome preparations. The tissues of the intestines, stomach, kidneys, and gills were found to be the most suitable for clastogenic studies. Phase contrast observations were made on the chromosomes of control mudminnows and mudminnows exposed to 325 R of X-radiation. The control rate of spontaneous chromosome aberrations was found to be low (about 0.03%). In contrast, fish exposed to 325 R of X-rays had aberrations in approximately 30% of the metaphases per fish examined. An apparent increase in clumping and a decrease in the mitotic index were also noted. It was concluded that the chromosomes of Umbra limi displayed typical responses to low level radiation exposure and that this fish would be an ideal cytogenetics model for this study of induced chromosome aberrations in fishes.