A few years ago, male smallmouth bass in the South Branch of the Potomac River were found to have eggs. Now a study of bass throughout the Potomac watershed has shown that the problem is not confined to the South Branch. Researchers tested smallmouth bass from the Shenandoah River, Monocacy River, and Conococheague Creek, and largemouth bass from the Potomac River in Washington, DC. Most of the male bass have eggs.
The causes are not well-understood, according to the article. While the researchers have found a number of pollutants that may be disrupting the fishes' hormonal systems, none has been conclusively linked to the problem. The effect this might have on humans is also unknown, and probably will not be known until the pollutant is identified. At the same time, the researchers indicated that the effect on humans would likely be far less than on the fish, since humans do not have the same exposure levels and have different hormonal systems. Still, it is reason to be concerned about the state of our water, and a reminder to be wary of eating local fish.
The results were striking, according to Vicki S. Blazer, a fish pathologist with the U.S. Geological Survey. More than 80 percent of all the male smallmouth bass they found were growing eggs, including all of the fish caught at four of the seven survey sites. The intersex condition doesn't change the fish's outward appearance but can be detected under a microscope.
At the site in Washington, seven of 13 male largemouth bass showed some kind of unusual feminine characteristic. Six of the seven fish tested positive for a protein used to produce eggs, and three of the seven contained eggs, Blazer said.
Taken together, Blazer said, the results on both bass species seemed to indicate that the Potomac watershed has a problem with "endocrine disruptors," contaminants that interfere with nature's chemical signaling. In this case, she said, the contaminants might have turned on bodily processes that normally are only active in female fish.