Mutagenicity testing of water with fish: a step forward to a reliable assay.

A step forward has been set towards the realization of a reliable "sister-chromatid" exchange (SCE) assay with fish for the detection of mutagens in water. This test can detect mutagenic contaminants in water without prior concentration steps. A healthy breeding stock of the tropical fish Nothobranchius rachowi has been set up in our laboratory. This fish is particularly suited for the SCE assay because of its low number of chromosomes. The major improvement consisted of the development of a reliable staining technique for the differentiation of sister-chromatids. The assay can now be used for research purposes. With a few improvements it can become a rapid low-cost test for the screening of effluents on contamination with DNA-damaging agents.

Some factors affecting optimal differential staining of sister-chromatids in vivo in the fish Nothobranchius rachowi.

In the past few years, routine studies of SCE induction in vivo in fish have been hampered by unreliable SCD techniques. This paper presents a number of modifications of the SCD technique in vivo in Nothobranchius rachowi. Major improvements were obtained by BrdU incorporation from aqueous solutions, short intervals between preparation and staining of slides and post-treatment with HCl. These improvements resulted in a highly reliable SCD procedure in Nothobranchius with a low level base-line SCE frequency (0.90 SCE/metaphase, 0.059 SCE/chromosome). Further research is now directed at gathering additional data on base-line SCE frequencies, establishing the sensitivity of the assay for aqueous solutions of known mutagens, and defining an experimental set-up for optimal statistical evaluation.

Toxicological assessment of river water quality in bioassays with fish.

A series of bioassays with fish was developed in order to evaluate toxicological aspects of polluted rivers in The Netherlands. A long term exposition of trout to riverwater under standardized conditions enables the detection of pathological effects such as growth retardation, liver and kidney enlargement and changes in clinical blood parameters. Bioaccumulation of heavy metals and organochlorine compounds can also be measured. Embryo-larval tests with trout were less suitable, because of yearly variations in egg quality. In the near future, sister chromatid exchange (SCE) assays in vivo with Nothobranchius may become available for the detection of mutagenic effects. It was possible to measure trends in toxicological quality of Rhinewater with these tests. However extrapolation of results to ecosystems and tracing of the causes of changes occurring in waterquality are still problematic.

Induction of sister-chromatid exchanges in fish exposed to Rhine water.

The induction was studied of sister-chromatid exchanges in gill and testis of fish exposed to Rhine water. The eastern mudminnow, Umbra pygmaea, was chosen because the usefulness of this species with a karyotype of 22 large chromosomes had been demonstrated in cytogenetic mutagenicity testing. Fish exposed to Rhine water for 3 and 11 days showed a 2-fold and 3-fold higher SCE rate resp., compared with fish exposed to ground water of drinking water quality. There was no difference in SCE rate between gill and testicular cells before and after exposure. GLC/MS analysis indicated that different classes of chemical compounds may be involved in the cytogenetic effects found in fish. The mudminnow has proved to be a useful fish species for biological monitoring of mutagens in polluted waters. The SCE test may be a suitable test system to prescreen their mutagenic potential.