Male fish from the upper reaches of the Potomac River are producing a blood protein normally found only in females, scientists say, seeming to confirm fears that an unknown pollutant is confusing the fish’s natural hormone systems.
This discovery, made by scientists at the Virginia Institute of Marine Science, comes on the heels of the finding last year that male fish in the same area were producing eggs.
Those intersex fish have put the Potomac River’s headwaters – small streams in West Virginia farm country – at the center of an emerging national pollution problem. Scientists say some runoff from factories, farms and sewage plants contains chemicals that animals’ bodies mistake for their own hormones, throwing off the natural signals that guide their development.
A recent experiment looked at smallmouth bass from the South Branch of the Potomac, the same species that previously had been found to be growing eggs there. Scientists were looking for another sign that something was wrong with the fish, to confirm that some male bass don’t exhibit this strange trait naturally.
“It should not be normal, but, of course, we didn’t really know,” said Vicki Blazer, a biologist at the U.S. Geological Survey who has led the research.
Scientists took blood from the South Branch fish, as well as from other male bass taken from two West Virginia rivers outside the Potomac watershed. The blood was tested for vitellogenin, a protein made in the livers of female fish.
Male fish have the vitellogenin-making gene but don’t usually have the female hormones that turn it on, scientists say. For this reason, other studies of abnormal fish across the country had used vitellogenin as a marker of abnormal development in males.
Among the Potomac fish, six of the 14 that were tested showed signs of the protein. Among the 17 fish taken from the other rivers, none tested positive for vitellogenin.