Weed killer feminizes fish

From New Orleans, La., at the E.Hormone 2002 meeting

DADDY-MOMMY. This mangrove killifish makes both sperm and eggs. W.P. Davis/EPA

The widely used herbicide atrazine can convert male frogs into hermaphrodites (SN: 11/02/02, p. 275: More Frog Trouble: Herbicides may emasculate wild males). But what happens when a naturally hermaphroditic species, such as the mangrove killifish, encounters this weed killer?

The hermaphrodites can change into females, new data show.

William P. Davis of the Environmental Protection Agency in Gulf Breeze, Fla., and his colleagues put killifish hatchlings in water with atrazine at a concentration of 16 or 33 parts per million for just 5 hours, then raised the fish until they laid eggs.

Ordinarily, these fish develop ovotestes, gonads that make both eggs and sperm. However, 30 percent of killifish exposed to atrazine developed no sperm-producing capacity but still could lay eggs. Davis says this is the first evidence of true adult females in this species.

The finding suggests that atrazine disrupted hormonal cues for testicular tissue. Though mangrove killifish with solely male gonads exist in the wild, they’re rare, Davis notes, so the new females’ eggs probably would never be fertilized.

The bursts of atrazine exceeded what would ordinarily occur downstream of any farm, Davis notes. His group is now investigating whether longer exposures to more environmentally relevant herbicide concentrations also yield the novel females.


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Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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