Feminized fish fail
In the early 1990s, biologists discovered male fish with egg-laden testes in rivers contaminated with sewage. Since then, this feminization has been observed around the world and linked to the presence of low-parts-per-trillion (ppt) levels of estrogenic chemicals, most notably natural and synthetic estrogen. But the significance of these effects on fish populations has remained a mystery.
Now, researchers have documented the catastrophic effect of chronic exposure to environmentally relevant estrogen levels on a population of minnows. The results, reported online on May 21 in Proceedings of the National Academy of Sciences U.S.A., indicate that existing concentrations of estrogens and estrogen mimics pose a serious threat to the sustainability of wild fish populations, according to the study authors.
Karen Kidd of the University of New Brunswick (Canada) and colleagues seeded a 34-hectare lake in Canada’s Experimental Lakes Area in northwestern Ontario with 5 ppt 17∝-ethynylestradiol—the active ingredient in birth control pills—starting in May 2001. Within weeks of the first doses, male minnows started making vitellogenin, an egg-yolk protein typically produced by female fish. Within 2 years, the protein concentration reached up to 10,000 times normal levels. The exposure delayed sexual development of both sexes and because minnows spawn for just one season during their 2-year life, this caused the population to plummet toward collapse in just 3 years. The minnow population took 2 years to recover after researchers stopped adding estrogen.
