Intersex small- and largemouth bass were found in waters near national wildlife refuges throughout the Northeast United States, according to a study from the U.S. Geological Survey (USGS) and the U.S. Fish and Wildlife Service (FWS). Of the fish tested, 85 percent of male smallmouth bass and 27 percent of male largemouth bass were intersex.
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 pesticides, pharmaceuticals or other chemicals disrupt the hormonal systems of an animal.
“It is not clear what the specific cause of intersex is in these fish,” said Luke Iwanowicz, a USGS research biologist and lead author of the paper, in a release. “Chemical analyses of fish or water samples at collection sites were not conducted, so we cannot attribute the observation of intersex to specific, known estrogenic endocrine-disrupting chemicals.”
Among the sites sampled were several locations in the Chesapeake Bay region, including near the Patuxent Research Refuge, Susquehanna National Wildlife Refuge and Rappahannock River Valley National Wildlife Refuge.
This study comes just after the release of a separate report from the Pennsylvania Department of Environmental Protection (DEP) and Pennsylvania Fish and Boat Commission identifying endocrine-disruptors, pathogens and parasites as the most likely causes for a decline of smallmouth bass in the Susquehanna River.
The USGS and FWS report, “Evidence of estrogenic endocrine disruption in smallmouth and largemouth bass inhabiting Northeast U.S. national wildlife refuge waters: A reconnaissance study,” is available online.
Scientists have found intersex fish in three Pennsylvania river basins, indicating hormone-disrupting chemicals are more widespread in the Chesapeake Bay watershed than once thought.
Image courtesy RTD Photography/Flickr
Intersex conditions occur when pesticides, pharmaceuticals or other chemicals disrupt the hormonal systems of an animal, leading to the presence of both male and female characteristics. The presence of intersex conditions in fish, frogs and other species is linked to land use, as the chemicals that lead to these conditions often enter rivers and streams through agricultural runoff or wastewater.
Previous samplings of fish in the region have found intersex conditions in the Potomac, Shenandoah and Susquehanna rivers, as well as lakes and ponds on the Delmarva Peninsula. On samplings conducted at 16 sites between 2007 and 2010, researchers with the U.S. Geological Survey (USGS) found intersex fish in the Susquehanna, Delaware and Ohio river basins.
According to the USGS, freshwater fish called white suckers from sample sites in the Delaware and Susquehanna river basins had a yolk precursor in their blood. Male smallmouth bass from all sample sites had immature eggs in their testes. The prevalence of intersex fish was highest in the Susquehanna river basin, which researchers attribute to the higher rate of farms—and related herbicides, pesticides and hormone-containing manure—in the area. While scientists found no relationship between the number of wastewater treatment plants in an area and the prevalence of immature eggs in fish, the severity of intersex conditions did rise at sites downstream from wastewater discharge points.
“The sources of estrogenic chemicals are most likely complex mixtures from both agricultural sources, such as animal wastes, pesticides and herbicides, and human sources from wastewater treatment plant effluent and other sewer discharges,” said fish biologist Vicki Blazer in a media release.
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.