Unsettling reports of “intersex” fish surface periodically in newspapers and scientific journals in scattered locations throughout the U.S. These freakish fish are typically males with immature egg cells in their testes. Occasionally they are female fish that display male characteristics.
Intersex fish are often found in waters contaminated by synthetic hormone-disrupting chemicals found in plastics, pesticides, personal care products, and more.
Turns out, these occasional reports are just the tip of the iceberg: In the most comprehensive study to date, U.S. Geological Survey (USGS) scientists probed 9 major American river basins, documenting widespread occurrence of intersex fish.
Intersex fish phenomenon is widespread
Intersex fish were spotted in nearly a third of sites examined. The USGS found afflicted fish in the Apalachicola, Colorado, Columbia, Mobile, Mississippi, Pee Dee, Rio Grande, and Savannah rivers and their tributaries.
Intersex largemouth bass were particularly prevalent in the Southeast, the USGS said. USGS scientists found that 91 percent of the largemouth bass in the Pee Dee River in South Carolina showed intersex characteristics. Some 60 percent of the largemouth bass population in the Apalachicola River in Florida were intersex, as were half the largemouth bass in Georgia’s Savannah River and the Rio Grande River in Texas.
Researchers found intersex problems in 73 percent of the smallmouth bass in the Mississippi River, 70 percent of smallmouth in Colorado’s Yampa River and 67 percent of smallmouth in the Columbia River in Oregon.
“We were surprised to see such high incidences,” Jo Ellen Hinck, a USGS biologist and the study’s lead author, told Environmental Working Group. “We’re concerned when we see the majority of fish at a site having this condition. It certainly makes us wonder what the bigger implications may be.”
Hormone-disrupting compounds in treated wastewater and agricultural runoff are suspected of playing a role in the broad prevalence of intersex fish. Laboratory tests document the development of intersex characteristics in fish exposed to individual hormonally-active chemicals, as well as to common combinations of these chemicals. Perhaps more disturbing, many of the same chemicals linked to intersex fish are also found in people’s bodies.
Something else to think about when you next pick up your fishing pole – or wait at the fish counter of your local grocery store.
PS – Want to read about intersex frogs? We have them, too.