Scientists Find Alternative Reason for Fish Kills

Posted: November 12, 1999 at 1:00 am, Last Updated: November 30, -0001 at 12:00 am

By Karen Louden Allanach

The micro-organism Pfiesteria piscicida has been blamed for killing large numbers of fish along the East Coast and causing human health problems for more than a decade. But a team of researchers from George Mason University, the American Type Culture Collection, and Virginia Commonwealth University (VCU) has identified another pathogen, Kudoa clupeidae, which may be the reason for fish kills that have been attributed to Pfiesteria.

Fishery biologists from VCU initiated the discovery after examining significant numbers of fish in the lower James River with ulcerative lesions, a symptom commonly associated with Pfiesteria’s toxic effects. Using a relatively new molecular technique similar to DNA fingerprinting, scientists were able to rule out Pfiesteria as a possible cause of the fish kills. Pfiesteria is suspected of releasing potent toxins that kill fish, but no traces of the organism were found in water and sediment samples. The Virginia Department of Environmental Quality confirmed these negative results.

Using samples from the James River, Thomas Nerad, ATCC protistologist, identified the microscopic parasite Kudoa from the lesions and muscle tissue of affected fish. “This parasite may have been overlooked in earlier studies because of the focus of the research community on Pfiesteria as well as on recent discoveries of other micro-organisms in menhaden fish lesions,” Nerad says.

Because of the high density of the pathogen in affected fish, researchers suspect that Kudoa may be one of the primary agents of infection in the recent event and may be responsible for previous outbreaks originally attributed to Pfiesteria. “We’ve thought for quite some time that fish kills may have been caused by a combination of environmental stress and alternative disease-causing organisms and not by Pfiesteria-produced toxins,” says Patrick Gillevet, research associate professor at the Institute for Biosciences, Bioinformatics, and Biotechnology. “These results support our hypotheses.”

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