Intersex fish widespread in Potomac River basin

The prevalence of intersex fish in the Potomac River basin has raised concerns about river health.

Intersex conditions, the presence of both male and female characteristics in an animal that should exhibit the characteristics of just one sex in its lifetime, occur when chemicals like pesticides, pharmaceuticals or personal care products enter the water and disturb the hormonal systems of fish and other species. Because the hormonal systems of fish are similar to those of humans, anomalies found in fish are an indication these chemicals may also pose a risk to people.

Image courtesy August Rode/Flickr.

According to a report released by the U.S. Geological Survey (USGS), intersex conditions in male smallmouth bass are widespread in the Potomac River basin: 50 to 75 percent of male smallmouth bass collected in the South Branch Potomac River exhibited signs of feminization, as did 100 percent of those collected at sites in the Shenandoah.

In the case of male smallmouth bass, the "intersex condition" reveals itself in the presence of immature eggs in the testes and of a certain protein--vitellogenin, normally found only in egg-laying females--in the circulating blood. Both conditions indicate exposure to chemical contaminants, and can result in reduced reproductive success or, in the case of a shorter-lived species like the fathead minnow, population collapse.

Intersex conditions have been linked to sewage flow from wastewater treatment plants and to runoff from farmland and animal feeding operations.

A popular sport fish, the smallmouth bass experienced spring kills in the Potomac and James rivers. A number of smallmouth bass collected during this survey were also observed with skin lesions, leading researchers to believe the fish may be a sensitive indicator of watershed health.

The USGS and Chesapeake Bay Program partners will use these findings to better identify chemical contaminants and their sources, planning to develop toxic contaminant reduction outcomes by 2013.

Learn more about the hormonal disruption of fish in the Chesapeake Bay watershed.