Male bass in Colorado River system showing feminine sex traits

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From The Denver Post (Bruce Finley):

This gender-bending was most common in the southeastern U.S. as well as in western Colorado, in the Yampa River, where 70 percent of male bass had eggs developing alongside their testicular organs, the U.S. Geological Survey study found. The causes aren’t clear, scientists said in the report in Aquatic Toxicology. Nor could they say whether “intersex” fish could reproduce.

But the extent of the intersex fish was startling, said Jo Ellen Hinck, the USGS biologist who led the project. “When we see 70 percent, we don’t think that’s normal,” Hinck said, referring to a sampling along the Yampa about 18 miles west of Craig.

The researchers studied 16 species, collecting data from 1995 through 2004 (funding was cut in 2006), and documented intersex characteristics in three other species, including catfish. Researchers with microscopes examined about 1,500 fish in nine river basins: the Apalachicola, Colorado, Columbia, Mobile, Mississippi, Pee Dee, Rio Grande, Savannah and Yukon. Only in the Yukon Basin in Alaska did researchers find exclusively male males. The intersex condition was most common in bass, with about a third of male smallmouth bass and a fifth of male largemouth bass showing eggs growing alongside testicular organs…

USGS scientists now must verify, using museum samples, whether intersex bass occur naturally, said David Norris, a University of Colorado professor of integrated physiology who has documented fish- gender distortions in Boulder Creek, Fountain Creek and the South Platte River. If not, “we’ve got a concern,” Norris said. “At these incredibly low levels of contamination, we’re starting to produce reproductive effects in animal populations…

Federal wildlife officials along the Yampa will consider possible sources of pollutants, said Tom Chart, director of the Upper Colorado River Endangered Fish Recovery Program for the U.S. Fish and Wildlife Service. “If we’re having these endocrine disrupters showing up in bass, it’s very likely they’re affecting native and endangered fish as well,” Chart said. “This is out of the natural balance.”

More water pollution coverage here and here.

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