SCIENCE BRIEFING

Almost one in five male black bass in American river basins has egg cells growing inside its sexual organs, a sign of how widespread fish feminizing has become.

The findings come from the U.S. Geological Survey in its first comprehensive examination of intersex fish in America, a problem linked to birth control pills and other hormone treatments that seep into rivers. Sporadic reports of feminized fish have been reported for a few years.

The new report was published online this month in Aquatic Toxicology.