The Chickahominy Report

News about Earth, Atmosphere, Water, and Life

Hormone may link fish kills, intersex fish in western Virginia rivers

Redbreast sunfish with Aeromonas salmonicida lesion above pectoral fin.

Redbreast sunfish with Aeromonas salmonicida lesion above pectoral fin.

MECHANICSVILLE, Va. — The mysterious fish kills that have afflicted the waters of western Virginia the past few years have returned, but this year federal and state researchers appear closer to determining their cause.

In May, anglers and fisheries biologists began reporting small numbers of dead fish and larger numbers of live fish with skin lesions from the North and South forks of the Shenandoah River; the North, Middle, and South rivers; and upper reaches of the James River. Smallmouth bass and redbreast sunfish have been hardest hit by the illnesses and deaths, but other species have been affected, too. Nevertheless, this year’s incarnation appears to be less severe — so far.

A similar syndrome of death and disease was first reported from the headwaters of the Potomac in 2002 and from the Shenandoah in 2004. During 2004 and 2005, nearly 80 percent of adult smallmouth bass and redbreast sunfish were lost. The first signs of disease were skin lesions caused by bacteria. The infection progressed until affected fish died. In ensuing years, fish kills have also been observed in the Cowpasture, Jackson, James, and Maury rivers.

In 2006 intersex fish — individuals with both male and female characteristics — were found in the Cowpasture, Maury, and Shenandoah rivers.

Over the years, an intensive search has been conducted by federal and state scientists for possible pathogenic or chemical causes of the disease that kills the fish. The first big break came last year, when Dr. Rocco Cipriano of the U.S. Geological Survey determined that the bacteria Aeromonas salmonicida was the primary pathogen present when disease symptoms and death were occurring among the fish. A. salmonicida causes furunculosis and other diseases characterized by skin lesions and septicemia (blood poisoning).

It is still not known whether the bacterial infection is a cause of the fish kills or if it is just associated with the conditions that lead to the fish deaths. A. salmonicida generally cannot survive the warm water temperatures typical of summer, so other research is seeking to find whether cold-water refuges — like springs — exist in the waters where the fish kills have occurred or whether the bacteria are reintroduced into the streams each year.

Rivers affected by fish kills in Virginia. (Virginia Department of Game and Inland Fisheries)

Rivers affected by fish kills in Virginia. (Virginia Department of Game and Inland Fisheries)

This week, a team of U.S. Geological Survey researchers found a possible link between chemical contamination in the rivers affected and the occurrence  of intersex individuals, skin lesions, and death of fish that has been observed since 2002. In a study published in the June 2009 issue of the journal Fish & Shellfish Immunology, a team led by Laura Robertson (Leetown Science Center, U.S. Geological Survey, Kearneysville, W.Va.) investigated whether estrogen and estrogen-mimicking chemicals could affect levels of hepcidin, a protein that regulates iron levels. Hepcidin is also believed to serve as part of the fish immune defense by either killing or restricting the growth of bacteria.

Robertson and colleagues found that, in largemouth bass, estrogen and estrogen mimics reduced production of one type of hepcidin and blocked production of another type. If these results are confirmed by further studies, it could link all phenomena observed when the fish kills occur and possibly point the way toward prevention or at least control of the problem by reducing pollution from estrogen and similar compounds.

Bill Hayden, public affairs director for the Virginia Department of Environmental Quality, viewed the results with caution, however.

“DEQ is aware of the investigations of intersex fish and whether they are connected with the fish kills in western Virginia rivers,” Hayden said. “We do not have sufficient evidence to identify estrogens or other endocrine disruptors as a cause of the kills, but the issue remains under investigation.”

— David M. Lawrence

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