Ethinylestradiol - a contraceptive for fish?

17alpha-Ethinylestradiol (EE2), a commonly used oral contraceptive, has been detected in sewage effluents at levels up to 10 ng/L. We used the zebrafish (Danio rerio) for Life-Cycle tests, as this species is a world-wide accepted model fish and completes its life-cycle in 3 month. Exposure to 10 ng/L EE2 during the period of morphological testis differentiation [42 - 71 day post fertilisation] caused a significant delay of spawning and a decrease in number of eggs and fertilisation rate. The effects elicited by a 4 week exposure appeared to be reversible, whereas an exposure to 10 ng/L for the first half year of life resulted in irreversible infertility: Even after 140 days in untreated water, fertilisation rates do not recover. The EC50 with respect to fertilisation rate was determined as 1.1 ng/L. At this concentration, being relevant for surface waters, also the number of spawned eggs was reduced and the time until first reproduction was significantly prolonged. Histological examination at different developmental stages disclosed effects on the gonadal level