Induction of sister chromatid exchanges in the central mudminnow following in vivo exposure to mutagenic agents.

Sister-chromatid exchange (SCE) studies using the central mudminnow, Umbra limi, demonstrated its usefulness as a model in vivo system for the detection of genetically active substances (mutagens and/or carcinogens). 5 days following the injection of 500 micrograms/g of 5-bromodeoxyuridine (BrdU), SCE rates were found to be quite low in the gills (2.0--3.3 SCEs/metaphase), kidneys (2.6--3.4 SCEs/metaphase), and intestines (3.7--4.5 SCEs/metaphase). However, after i.p. exposure to microgram quantities of methyl methanesulfonate (MMS) or cyclophosphamide (CP), large linear dose-dependent increases in SCE rates were observed in all tissues examined. amined. On a microgram/g basis, CP was found to be a 2--4 times more potent inducer of SCE than was MMS. Studies involving the addition of neutral red dye (NR) to the fish's aquarium water revealed that the mudminnow could concentrate the dye in its gill and kidney tissues. This dye was found to cause significant increases in SCE rates at water levels of less than 0.1 ppm. However, the concentration of dye in the tissues did not show a correlation with the SCE rate. Possible explanations for this observation are presented in the text. These findings demonstrate the feasibility of using a fish such as the mudminnow to investigate cytogenetic consequences of aquatic pollution.