OSU researcher develops new way to detect salmon parasite

December 1, 2004

CORVALLIS—Researchers at Oregon State University have developed a molecular method to detect and measure a salmon and trout parasite thought partially responsible for controversial salmon die-offs in the Klamath River.

As many as 30 to 40 percent of fish captured in the lower Klamath River are infected with one particular myxozoan species, Ceratomyxa shasta, explained Jerri Bartholomew, a researcher in OSU's Department of Microbiology and the Center for Fish Disease Research.

Until now, researchers had no quick, easy way to test for the parasite in water samples. Using the organism's own DNA, this newly developed assay can detect even 1/1000th of a parasite spore in a water sample.

To detect Ceratomyxa shasta prior to this breakthrough, scientists had to maintain fish in cages along areas of the river suspected to be infectious, then return them to the laboratory and wait for months to see if clinical signs appeared. There was no way to quantify the number of infectious spores moving through the water.

"This is a huge jump in what we're able to do," said Bartholomew. "We wanted to offer a tool that would be useful if managers were to test management options like altering flows at certain times of year, so that effects could be determined immediately."

Natural resource managers welcome the new tool.

"Jerri's doing cutting-edge research that provides us with an accurate tool to assess spore levels quickly," said Scott Foott, a U.S. Fish and Wildlife Service pathologist. "Without advances like this, all we can do is limp along and quantify dead fish, which doesn't allow us to do any innovative management."

Bartholomew and her colleagues have discovered that Ceratomyxa shasta is not evenly distributed throughout the Klamath. "The parasite's life cycle is only established in the main stem of the Klamath, not the tributaries," said Bartholomew.

The OSU researchers also have found that the dams on the Klamath appear to act as a partial barrier to Ceratomyxa shasta.

"Above the dams, the parasite is still present, but the severity of infection drops off," she explained.

The research group is using information from the new method to determine the unusual distribution pattern. An additional clue to its distribution may come from Ceratomyxa shasta's unique ecology. It has two hosts – salmonid fish and a type of aquatic worm.

"We think the distribution is determined by habitat requirements of the worm host," Bartholomew said.

So far, the scientists do not know how the various tributary salmon populations are affected by disease problems in the main stem Klamath River. They say that knowing the distribution pattern of the salmon parasite is critical for future management.

Bartholomew and her colleagues are planning on investigating why the infection is localized in the main stem. They are also interested in testing management actions that might reduce parasite levels.

One example might include a large-scale flow experiment, not unlike the flushing flow water releases researchers conducted from the Glen Canyon dam on the Colorado River a few years ago. This would allow them to better understand how the normal hydrology of the river system controls the number of worm hosts.

Salmon from the tributaries of the Klamath River are distinct salmon populations and are important to maintain each species' genetic diversity, explained Foott. Unfortunately, the survival rate for Ceratomyxa shasta-infected salmonids is not good.

"If it's infected in the main stem Klamath River," Foott said, "it's probably dead."

Author: Virginia Gewin
Source: Jerri Bartholomew