'Intersex' Fish Found In Many Rivers

September 15, 2009

Release from: David A. Fahrenthold
Washington Post

Federal researchers have found "intersex" fish -- with both male and female characteristics -- in rivers from the deep Southeast to the Pacific Northwest, indicating that a condition found in the Potomac River is more widespread than previously known.

The largest-ever study looking for intersex characteristics, conducted by the U.S. Geological Survey, examined the Apalachicola, Colorado, Columbia, Mobile, Mississippi, Pee Dee, Rio Grande, Savannah and Yukon river basins. Among those, the Yukon was the only river in which no abnormal fish were found, the agency said Monday.

The fish most affected seemed to be smallmouth bass, among which a third of male fish were found to be growing eggs. The study did not investigate the cause for these conditions; scientists suspect that man-made pollutants from factories, farms or sewage plants may be driving natural hormone systems haywire.

The Potomac River was not tested in this survey. Previous studies have indicated that more than 80 percent of the river's male smallmouth bass are growing eggs.