Intersex condition spreads among Potomac smallmouth

Recently completed research on the presence of female reproductive cells in male smallmouth bass has led fisheries scientists to conclude that the "intersex condition" is now present throughout the Potomac River's expansive watershed.

Potomac River

WASHINGTON — Recently completed research on the presence of female reproductive cells in male smallmouth bass has led fisheries scientists to conclude that the "intersex condition" is now present throughout the Potomac River's expansive watershed.

 However, scientists were unable to pinpoint the exact cause of the condition, nor do they know if it will have an adverse impact on bass populations in the popular fishery.

 The research was conducted by scientists from the U.S. Fish and Wildlife Service (USFWS), the U.S. Geological Survey, the Maryland Department of Natural Resources (MDNR), the West Virginia Department of Natural Resources and the University of Florida, and it was reported in the May 2009 edition of the scientific journal, Environmental Toxicology and Chemistry.

The intersex condition is indicated by the presence of testicular oocytes, or TOs, in male bass. Normal, healthy males do not have oocytes, which are female reproductive cells.

"At the moment, we don't know the ecological implications of [intersex condition]," said Leopoldo Miranda, the director of the USFWS Chesapeake Bay Office. "It could potentially affect the reproductive capability of important sport fish species in the [Potomac River] watershed."

The research was based on analysis of water and fish tissue samples obtained in 2005 and 2006 from five locations in the Potomac River watershed.

Two sampling sites were upstream and downstream from a wastewater treatment plant along the Monocacy River, a Maryland tributary of the Potomac River, and two more were upstream and downstream from another treatment plant along Conococheague Creek, another Potomac River tributary, which originates in Pennsylvania. In addition, largemouth bass were collected downstream from Washington's Blue Plains plant, a warmer, tidal section of the Potomac River that contains few smallmouth bass.

Of the male smallmouth collected, close to 100 percent had TOs in their bodies. By contrast, only 23 percent of male largemouth contained TOs. The researchers do not yet understand the disparity.

In spite of the disturbing research results, the Potomac River and its tributaries, including the Monocacy River and Conococheague Creek, remain premier destinations for smallmouth bass anglers, said John Mullican, a study participant and a large-river fisheries biologist for MDNR. He said Potomac River smallmouth population is at a 20-year high, and the 2007 smallmouth bass hatch was the largest recorded in 33 years.

The authors of the 2009 research report stressed that "a key research question is whether [Potomac River watershed] smallmouth and largemouth bass populations are adversely affected by the presence of [intersex condition] in sexually mature males."

The research team has already begun sampling largemouth and smallmouth bass captured from largely pristine waters near National Wildlife Refuges from Virginia to Maine. Results should be available in 2011.

Scientists were surprised to find that male smallmouth from a federal hatchery in Kansas also possessed the intersex condition. "To our knowledge, this is the first time that intersex has been identified in hatchery-raised fish," the authors of the 2009 report wrote. Additional research in this area is planned as well.

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