The Chickahominy Report

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)

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