To gauge the toxicity of Pfiesteria, the important single-celled fish predator that was the culprit behind a number of fish kills and fish diseases along the East Coast in the 1990s, researchers need to both use the proper study methods and recognize that certain populations of the organism, called strains, are toxic while others are not.

That's the main result of a wide-ranging study by Dr. JoAnn M. Burkholder, professor and director of the Center for Applied Aquatic Ecology at North Carolina State University, along with a dozen colleagues from several universities and research institutions, and a federal laboratory specializing in marine toxins.

The research is published online in Proceedings of the National Academy of Sciences.

The study reaffirmed that some strains of the two known Pfiesteria species are toxic, including a strain used by other researchers who had asserted that Pfiesteria can't make toxin. Burkholder and her colleagues found that toxic Pfiesteria strains can produce toxin in the absence of bacteria or other contaminating microbes, and that small amounts of Pfiesteria can kill fish with toxin. They also showed that toxin from Pfiesteria can cause fish disease and death without Pfiesteria cells having to be present: water that at one time contained Pfiesteria, but was then completely filtered to remove all of the toxic Pfiesteria cells, caused lesions in fish.

Other experiments showed that purified Pfiesteria toxin residue added to cultures of larval fish killed the fish, while control fish without exposure to the toxin remained healthy.

In the study, two basic methods of detecting Pfiesteria toxicity were compared: fish microassays (FMAs) using larval fish, and standardized fish bioassays (SFBs) using juvenile fish. In each method, the scientists tested toxic Pfiesteria strains, known to be toxic from toxin detection tests that were completed by the National Oceanic and Atmospheric Administration's Nationa
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Contact: Dr. JoAnn M. Burkholder
joann_burkholder@ncsu.edu
919-515-2726
North Carolina State University
14-Feb-2005

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