Zebrafish Danio rerio and roach Rutilus rutilus: Two species suitable for evaluating effects of endocrine disrupting chemicals?

Morphological studies of gonads from roach (Rutilus rutilus) in a small Swedish lake were performed. The lake is a potential recipient for drainage water from a refuse dumping area. All fishes were macroscopically identified as males, but histological examination of the gonads showed a high incidence of intersex. This high incidence might be caused by endocrine disrupting chemicals. The relationships between exposure to endocrine disrupters and intersex observations in wild fish is unknown and the effect of endocrine disrupters on zebrafish (Danio rerio) were evaluated in order to determine whether they might serve as a model laboratory species for effects of endocrine disrupting chemicals in wild fish. Zebrafish were exposed from pre-blastula stage until sexual maturation to either standardised water (controls), 17a-methyltestosterone (1, 10 mu g l super(-1)) or 17b-estradiol (1, 10 mu g l super(-1)). Exposure to both concentrations of 17b-estradiol caused a significant feminisation, while a significant increase in the proportions of males was found after exposure to 1 mg 17a-methyltestosterone l super(-1). Furthermore, exposure to 1 and 10 mg 17a-methyltestosterone l super(-1) caused development of intersex individuals. Additionally, sexually mature male zebrafish were exposed to 1 mu g 17b-estradiol l super(-1). After 10 weeks of exposure the fish were transferred to non-contaminated water for two weeks. The control group was kept in standardised water for 12 weeks. At termination of the experiment, measurement of whole-body vitellogenin concentrations were performed. Exposure to 17b-estradiol caused a significant increase in whole body vitellogenin concentrations. After 2 weeks in water without addition of 17b-estradiol, the vitellogenin concentration was reduced by approximately 50%. Roach and zebrafish may share properties which makes these species suitable for further comparisons to evaluate effects of endocrine disrupting chemicals as well as domestic and industrial effluents containing hormone-like substances.