RESTON, Va., Sept. 14 (UPI) -- A U.S. Geological Survey study has found intersex in smallmouth and largemouth bass to be widespread in numerous U.S. river basins.
USGS scientists said their finding is the result of the most comprehensive and large-scale evaluation of the condition, which is primarily revealed in male fish having immature female egg cells in their testes, and occasionally female fish with male characteristics as well.
Of the 16 fish species researchers examined, they said the condition was most common in smallmouth and largemouth bass.
The scientists said the found intersex fish in about a third of all sites examined, which included the Apalachicola, Colorado, Columbia, Mobile, Mississippi, Pee Dee, Rio Grande, Savannah and Yukon River basins. The Yukon River basin was the only one where researchers did not find at least one intersex fish.
The researchers said they also documented intersex in channel catfish for the first time.
"Although the USGS has already documented the severity of intersex in individual basins such as the Potomac, this study reveals the prevalence of intersex is more widespread than anyone anticipated," said Sue Haseltine, the USGS associate director for biology. "This research sends the clear message that we need to learn more about hormonal and environmental factors that cause this condition in fish, as well as the number of fish afflicted with this condition."
The study appears online in the journal Aquatic Toxicology.