Long-Term Exposure to Estrogen Causes Reproductive Failure in Fish

Long-term exposure to a synthetic estrogen at levels below those currently found in the environment may have a major impact on fish populations, according to a study accepted today for publication in the December issue of the peer-reviewed journal Environmental Health Perspectives (EHP). The study shows that ethynylestradiol, a potent form of estrogen used in oral contraceptives, can produce sexually compromised males.

Researchers exposed zebrafish to low concentrations of the hormone over three generations and measured the effects. After 210 days, or a full zebrafish lifetime of exposure to ethynylestradiol, second-generation fish showed reduced fertility. In addition, out of nearly 12,000 eggs spawned, none were viable. Upon examination, researchers found that none of the second-generation male fish had normal testes, and they did not produce expressible semen. However, the fish showed normal reproductive behavior patterns, including competing with healthy males.

This research suggests that the development of the testes is more sensitive to disruption by ethynylestradiol than is reproductive behavior. This could have significant population-level consequences, as infertile males have a significant ability to interfere with breeding dynamics. “Previous studies in fish have shown that endocrine disruptors can reduce sperm counts and induce female-specific proteins in males,” said Dr. Jim Burkhart, science editor for EHP. “But until now little evidence existed to show that environmentally relevant concentrations of endocrine disruptors could induce such changes and actually reduce fertility.”

The lead author of the study was Jon P. Nash, of the Katholieke Universiteit Leuven in Belgium. Other authors were David E. Kime, Leo T.M. Van der Ven, Piet W. Wester, François Brion, Gerd Maack, Petra Stahlschmidt-Allner, and Charles R. Tyler.

EHP is published by the National Institute of Environmental Health Sciences, part of the U.S. Department of Health and Human Services. EHP is an Open Access journal in January 2004.