Potomac’s intersex fish a puzzle for scientists

Something strange is brewing among the fish in the Potomac River. Male fish are producing eggs, and scientists are trying to figure out why.

Scientists are studying a sex-bending phenomenon called “intersex” in the river in rural Western Maryland and West Virginia, said Vicki Blazer, fish pathologist with the U.S. Geological Survey.

The discovery of intersex fish suggests that hormones and other pollutants may be directly harming the ecology of the Chesapeake Bay watershed, she said.

But researchers aren’t sure what causes the sex change and what it means for the future of the Bay.

“It’s as complex a scientific puzzle as you can try to solve,” said Pat Campbell, assistant director of the West Virginia Division of Water and Waste Management. “You just kind of have to play detective and work on it piece by piece.”

In 2003, Mrs. Blazer led a group that first identified the phenomenon among smallmouth bass in the Potomac headwaters in West Virginia.

Since then, scientists have noticed the phenomenon among up to 80 percent of the smallmouth bass at about 10 sites along the south branch of the river, Mrs. Blazer said. This spring, they pinpointed intersex fish at a site downstream from Hagerstown.

Several studies also have found levels of a protein called vitellogenin in a high percentage of male fish, Mrs. Blazer said. Vitellogenin is produced in the eggs of female fish.

The anomalies probably indicated high amounts of synthetic estrogen, such as birth control, and other chemicals in the river, Mrs. Blazer said. She said people in towns where the river is connected to drinking water are especially concerned.

“I’ve had Rotary clubs and water boards asking me about [what the phenomenon means for the river],” Mrs. Blazer said. “So many of the chemicals we commonly use have the ability to cause it.”

Mr. Campbell said the phenomenon could be attributed to several factors, besides contaminants. Researchers must conduct further studies to find the cause, he said.

He said research has not found chemicals or additives in the river exceeding legal limits.

But little work has been done to examine the water itself, Mrs. Blazer said.

This fall, the Maryland Department of Natural Resources and the U.S. Fish and Wildlife Service will conduct a study on water quality that could shed light on the river’s contents.

In 1995, U.S. Geological Survey scientists in Arizona released a study documenting sex changes among fish in the Colorado River, downstream from Las Vegas.

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