Investigators seeking causes of recurrent massive die-offs of fish and water birds at California's Salton Sea may have identified a principal culprit, according to Dr. Milton Friend, director of the National Wildlife Health Center.

The finding comes as a new die-off of tilapia, the predominant fish species in the Salton Sea, has been reported with more than one million dead fish over a three-mile stretch at the north end of the Sea, Department of the Interior officials said.

Drs. Tonie Rocke and Lynn Creekmore, scientists from the US Geological Survey's National Wildlife Health Center (Madison, Wis.), conducted a field investigation in late August that focused on collecting sick or freshly dead fish from locations where most of the bird mortality was occurring. In collaboration with NWHC studies, Dr. Jan Landsberg, a research scientist in aquatic health at the Florida Department of Environmental Protection, examined gills from 23 fish collected at the Salton Sea for parasites. She found 22 to be infested with moderate to high levels of a lethal parasite of warm-water marine fish.

The parasite, a dinoflagellate known as Amyloodinium ocellatum, is recognized as a persistent disease-causing agent that causes serious mortalities in fish-farming facilities and public or home marine aquaria. Under closed conditions, such as aquaria and apparently also in the Salton Sea, the investigators reported, parasite levels can build up to extremely high levels in fish. Healthy fish in aquaria can die after only 12 hours of exposure to Amyloodinium.

Like other USGS science centers, the National Wildlife Health Center has a primary responsibility for assisting the public land managers of the Interior Department. "Because a national wildlife refuge occupies a signific
'"/>

Contact: Duncan Morrow
Duncan_Morrow@nbs.gov
703-648-4221
United States Geological Survey
10-Sep-1997