Many of the fish lesions in Chesapeake Bay may be caused by a fungal infection rather than Pfiesteria, a U.S. Geological Survey scientist reported recently at the International Symposium on Aquatic Animal Health Conference in Baltimore. While Pfiesteria remains the primary cause of fish kills in the Chesapeake, North Carolina and other estuaries, a fungus seems to be primarily responsible for lesions in menhaden fish of the Chesapeake Bay.
Vicki Blazer, a fish pathologist at the USGS Leetown Science Center in West Virginia, found fungal infections in 95 percent of the lesioned menhaden sampled from river sites closed by Maryland in 1997 and in 100 percent of the lesioned menhaden sampled from the Pocomoke and Wicomico rivers in August 1998. In early October, USGS scientists will collect additional samples from the Bay.
The fungus, said Blazer, appears to be a pathogenic species of Aphanomyces that has caused identical lesions and fish kills of estuarine and freshwater cultured and wild fishes throughout the Indo-Pacific area, including Japan, Australia, India and Thailand. These fish die-offs in the Indo-Pacific have been occurring since the 1970s in some countries and became a serious recognized problem in the 1980s. In a decade when problems caused by invasive species are becoming increasingly evident, Blazer questions how this fungus may have become established in Chesapeake Bay tributaries and what water-quality factors, including nutrients and dissolved oxygen, may be involved in such disease outbreaks.
In the Chesapeake Bay fishes that Blazer examined, the fungal organism and the
surrounding sore often extended deep into the fishes muscle under intact normal
skin. "In numerous fishes," Blazer said, "the
fungal organism had actually penetrated to and through organs such as the liver.
Future research will help determine if large numbers of migrating menhaden with
open skin sores -- such as those caused by the fungal infection
'"/>
Contact: Catherine Haecker
catherine_haecker@usgs.gov
(703) 648-4283
United States Geological Survey
30-Sep-1998