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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