Scientists Find Possible Link between Intersex Fish and Fish Kills in Potomac, Shenandoah Rivers

U.S. Geological Survey researchers have found a possible connection between the occurrence of intersex fish and fish kills and lesions on bass in the Potomac and Shenandoah rivers.

In a recently published study, USGS researchers showed that largemouth bass that were injected with estrogen produced lower levels of a hormone called hepcidin. In addition to regulating iron in mammals, hepcidin is suspected to act as an antimicrobial peptide in fish, frogs and mammals. Antimicrobial peptides are the first line of defense against disease-causing bacteria, fungi and viruses.

“Our research suggests that estrogen-mimicking compounds may make fish more susceptible to disease by blocking production of hepcidin and other immune-related proteins that help protect fish against disease-causing bacteria,” said Dr. Laura Robertson, a USGS genomics researcher who led the study.

The study showed that the estrogen blocked the production of hepcidin in fish that were exposed to bacteria, giving more weight to the theory that estrogen or estrogen-mimicking chemicals could be making fish more susceptible to diseases, according to Robertson.

USGS researchers found intersex fish -- or fish with both male and female reproductive traits -- in the Potomac and Shenandoah rivers several years ago. Studies have shown that estrogen and estrogen-mimicking compounds can cause intersex traits to appear in fish.

Because fish lesions, fish kills and intersex traits have been found to co-occur in the Potomac and Shenandoah rivers, USGS scientists have theorized that estrogen-mimicking compounds could also be involved in lesions and fish kills.

Birth control pills, hormone replacements and hormones from livestock operations are a few possible sources of estrogen and estrogen-mimicking chemicals. These chemicals are found in treated wastewater, as they are not removed during normal sewage treatment processes.

Learn more about this USGS study.