Fish kill inquiry grows complex

Kudoa, not Pfiesteria, tied to Va. incident

November 10, 1999|By Joel McCord | Joel McCord,SUN STAFF

The discovery of a parasite responsible for a fish kill in Virginia last month has thrown another variable into attempts to understand the toxic microbe Pfiesteria piscicida.

Although signs pointed to Pfiesteria, Virginia scientists found that Kudoa, a parasite more often associated with fish ponds than Chesapeake Bay tributaries, killed hundreds of menhaden in the James River between Newport News and Hampton Oct. 20-22.

"The salinity in that part of the river was right [for Pfiesteria]; it was warm and shallow, and it was fall, the same time of the year we had the other events," said Greg C. Garman, a Virginia Commonwealth University fish biologist.

But the scientists ruled out Pfiesteria within 24 hours and continued testing until they found Kudoa, a parasite that has been "known to science for about 50 years," Garman said.

While some scientists believe Pfiesteria emits a toxin that is harmful to people, there is no evidence that Kudoa presents a threat to public health.

Garman's announcement was made two weeks after a legislator from Maryland's Eastern Shore held a news conference to call attention to a scientific study that questions whether lesions on dead fish on the lower shore in 1997 were caused by Pfiesteria or by a fungus called Aphanomyces.

Garman said he would not "try to rewrite history," but argued that if Kudoa caused the fish kill in the lower James "it is at least possible" that it could have been involved in "events from two or three years ago."

"We believe there is a growing amount of evidence that Pfiesteria is a piece of the puzzle, but no longer [all] the puzzle," he said.

JoAnn Burkholder, a researcher at North Carolina State University, agreed that "fish kills and fish-disease events that look similar to Pfiesteria could be caused by many things," but insisted the fish kills in the Pocomoke and Chicamacomico rivers were caused by Pfiesteria.

"We carefully and rigorously evaluated our information with lots of corroboration," said Burkholder, who helped discover Pfiesteria in the 1980s. "Our research has been cross-confirmed, peer reviewed and internationally published."

This is not the first time Kudoa has been identified in dead fish, said Dave Goshorn, chief of the living resource assessment program for the Maryland Department of Natural Resources. Researchers last summer found the parasite in menhaden in Maryland waters.

That doesn't discount Pfiesteria, but raises questions about how the microbe, the parasite and the fungus relate to one another, Goshorn said.

"Does Pfiesteria cause the lesions, or do the presence of lesions induce Pfiesteria?" he asked. One thing is clear, he said: "Where we have had confirmed toxic outbreaks of Pfiesteria, there is a large percentage of fish with lesions, making it very complicated to identify cause and effect."

And while suggestions that the fish kills in the Pocomoke might not have been entirely caused by Pfiesteria, scientists say, that would not rule out pollution caused by nutrients as a major source of the trouble.

High levels of nutrients have been associated with the algal blooms that are present when Pfiesteria turns toxic, and Kudoa is associated with the excrement-rich ponds of fish farms.

Kudoa is more prevalent "when you try to culture fish in closed, high-density conditions where water quality can get pretty bad," Garman said.

The parasite is not nearly as common in natural conditions, Garman said.

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