Scientists differ on role of Pfiesteria

Microbe might not be culprit in Md. fish kill


The victims thrashed wildly until at last they expired, their silvery remains, pocked with open sores, littering the lower Pocomoke River in August 1997.

Investigators quickly pointed to Pfiesteria piscicida, a single-celled algae blamed for fish kills in estuaries behind North Carolina's Outer Banks in the 1980s.

Almost as quickly, state and federal agencies awarded millions in research grants in an effort to unlock the mysteries of the microbe.

Now some researchers are saying that they misidentified the culprit. The allegation has sparked a debate among high-profile scientists and heightened competition for research grants.

Maryland Department of Natural Resources scientists contend that Pfiesteria killed the fish in the Pocomoke, but two sets of scientists have advanced competing theories.

Still others have seen fish die in the presence of Pfiesteria but without the telltale lesions, and none of the researchers has been able to figure out the chemical composition of Pfiesteria's toxin.

"Pfiesteria has been blown out of proportion, at least in the Chesapeake," says Vicky S. Blazer, a fish pathologist with the U.S. Geological Survey.

Wolfgang Vogelbein of the Virginia Institute of Marine Science, in a recent speech to the Chesapeake Bay Commission, stopped just short of asserting that Pfiesteria had nothing to do with the Pocomoke fish kill.

In the December issue of the Journal of Aquatic Animal Health, Vogelbein and Blazer say that Aphanomyces invadans, a fungus responsible for fish kills in Asia, was the cause of the lesions. If anything, Pfiesteria might have provided the fungus with a way to get into the fish, the scientists say. "If Pfiesteria played a role, it was an early role," says Vogelbein, "and it may not have played a role at all."

The dispute, in which it seems that few scientists agree on anything, demonstrates the depth of the mystery surrounding the microbe and the volatility of high-profile science, with its fierce competition for grants and recognition.

Pfiesteria is a one-celled organism that researchers believe has 24 life forms, one or two of which are toxic. It lies dormant in bays and rivers until conditions are ripe -- warm, slow-moving water is overloaded with nutrients, causing algal blooms -- then turns toxic and attacks fish.

In search of clues

Researchers at the University of Maryland Biotechnology Institute say they have conducted experiments in which fish died in the presence of Pfiesteria but without telltale lesions.

"The fish kills have been associated with Pfiesteria, but there has been no direct connection," says Gerardo Vasta, a professor at UM's Center of Marine Biotechnology at the Columbus Center in Baltimore. The main problem, he says, is that scientists have not been able to figure out the chemical composition of the toxin.

John S. Ramsdell, a toxicologist at the National Oceanic and Atmospheric Administration's Marine Biotoxins Laboratory in Charleston, S.C., says it is likely that Pfiesteria produces a toxin, judging from the way fish suffer in the laboratory.

But because no one has figured out its chemical structure, "the final nail in the coffin is not there," he says.

There is an apparent link between Pfiesteria and people sickened during the outbreak on the Pocomoke River in 1997, but no proof, says Glenn Morris, lead scientist in a National Institutes of Health study of the cause of diseases associated with Pfiesteria exposure.

About two dozen people complained of memory loss and confusion, symptoms that Morris says were "linked to their exposure to the Pocomoke" when Pfiesteria was present.

In October, scientists from Virginia Commonwealth University found that Kudoa, a parasite more common to fish ponds than to the Chesapeake Bay and its tributaries, was responsible for a fish kill in the James River, despite signs that pointed to Pfiesteria. They suggested that Kudoa could have been responsible for the Pocomoke fish kills.

Joanne Burkholder, a North Carolina State University researcher who helped discover Pfiesteria, scoffs at the suggestion.

"The fish [in the James River] showed none of the field symptoms we look for," she says. "The people who reported it had never seen toxic Pfiesteria. They were trying to debunk an issue they know nothing about."

Burkholder says the Chesapeake Bay is a "fringe area" for toxic Pfiesteria outbreaks because its geographic characteristics differ from those in North Carolina.

The waters behind the Outer Banks, where the deaths of a billion fish have been attributed to Pfiesteria, don't flush as well as the Chesapeake, enabling nutrients and other pollutants to build up and grow more of the algae that Pfiesteria feeds on.

What Aphanomyces, Pfiesteria and Kudoa have in common are the conditions under which they thrive: warm, brackish water loaded with nutrients.

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