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The suspect. Pfiesteria's role in massive fish die-offs continues to generate debate.

Fish-Killer's Weapon Revealed?

A team of researchers claims to have new evidence that a toxin produced by a one-celled marine organism called Pfiesteria is responsible for massive fish die-offs on the East Coast of the United States. But the new studies, which include a rough sketch of the toxin, have failed to convince skeptics that this substance harms wild fish or people.

For 10 years, aquatic ecologist JoAnn Burkholder of North Carolina State University in Raleigh has argued that the dinoflagellate Pfiesteria has killed more than a billion fish in East Coast estuaries and has sickened lab workers and fishers with a potent neurotoxin. However, despite years of effort, the toxin has not been identified. This past summer, doubts escalated when researchers at the Virginia Institute of Marine Science (VIMS) in Gloucester Point and other universities reported in two top journals that they could not find a toxin, and that Pfiesteria can kill fish by feeding on them (Science, 11 October, p. 346).

Last week at the 10th International Conference on Harmful Algae in St. Petersburg, Florida, Burkholder argued that her critics had not established the right conditions for making Pfiesteria produce toxin. Her lab coaxed the strain of Pfiesteria shumwayae used in the VIMS experiments to kill fish much faster--in less than 4 hours, compared to the 24 to 48 hours reported by VIMS scientists. Collaborating chemists from the National Oceanic and Atmospheric Administration in Charleston, South Carolina, partially described a toxic chemical isolated from water containing the fish-killing Pfiesteria. It appears to be a glycoside, a molecule that's half sugar, half some other chemical group that hasn't been identified.

Other algal toxin researchers remain skeptical. Wayne Carmichael of Wright State University in Ohio says that while some algal toxins are glycosides, this kind is unlikely to cause the neurotoxic effects reported in fish and humans. "It would not explain the range" of observations, he says. And VIMS fish pathologist Wolfgang Vogelbein points out that nobody has yet shown that this purified toxin produces the kind of sores he sees on fish physically attacked by Pfiesteria.

Burkholder's critics say that the solution to the debate is for other groups to test her toxic strains. But Burkholder, who has long been criticized for not sharing her strains, still seems reluctant. She noted at the meeting that the VIMS strain, which she says is toxic, is freely available and advised other scientists to follow her protocols for culturing the microbe.

Related sites
Burkholder lab
VIMS Pfiesteria research
The Harmful Algae Page