- The Washington Times - Saturday, February 28, 2004

BALTIMORE (AP) — Researchers say they are carefully considering whether to introduce Asian oysters into the Chesapeake Bay after discovering that the species is susceptible to parasites related to one that is ravaging the Bay’s native oysters.

Researchers from the Virginia Institute of Marine Science said genetic and other studies of the Asian oysters have found two parasites related to the protozoan that produces deadly Dermo-disease infections in Bay oysters. Some also have a herpes virus that could be fatal to oyster larvae in hatchery environments.

“We want to be careful not to introduce any hitchhikers, pathogens or parasites as we bring in these stocks,” said Ryan Carnegie, a research team member at the Virginia Institute of Marine Science.

The researchers studied samples from five sites in China and Japan. Those infected were suffering light infections, Mr. Carnegie said.

“The real issue isn’t that they have a parasite. I think we assumed that we were going to find something,” Mr. Carnegie said. “The real issue is, what are we going to do about it here so we don’t introduce a new pathogen into the environment?”

Researchers presented their findings Wednesday in Laurel to more than 160 scientists who gathered for a Chesapeake Bay fisheries research symposium at Patuxent Wildlife Refuge.

Chris Judy, the shellfish program director at the Maryland Department of Natural Resources, said U.S. scientists knew the Asian oysters could be infected by a Perkinsus protozoan native to Virginia waters without significant mortality.

“The news is that Dermo — Perkinsus — is in China and Japan. That was news to everybody,” Mr. Judy said.

The federal government has been gathering comments for an environmental impact study to assess the risks of putting Asian oysters into Chesapeake waters.

The population of the Bay’s native oyster has diminished because of Dermo and MSX, another parasitic disease.

Last year’s oyster harvest in Maryland was 53,000 bushels, down from as many as 2.5 million bushels just two decades ago.

Watermen have been urging scientists to quickly assess the impact of introducing the Asian species, which appear resistant to MSX and Dermo.

Though the Asian oysters appear to tolerate the infections and remain healthy, scientists don’t know the impact the microbes could have on the local oysters, Mr. Carnegie said. The Asian parasite may also infect native clams or other species.

Risks will be assessed in a two-year study at the Center of Marine Biotechnology in Baltimore, under a contract with the state Department of Natural Resources.

A key issue will be determining whether the Asian oyster is really resistant to the Perkinsus protozoan that causes Dermo, center director Yonathan Zohar said.

“What happens if conditions become extreme, if temperatures or salinity go out of range or they’re exposed to any kinds of contaminants?” Mr. Zohar said. “That may result in compromising the immune response of the oysters, and then they become much more susceptible.”

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