December 3, 2004

Researchers Develop Salmon Parasite Test

PORTLAND, Ore. (AP) -- A new test could help scientists determine more quickly whether chinook salmon in the Klamath River are infected with a potentially deadly parasite.

Previously, it took months to determine if the salmon contained the parasite Ceratomyxa shasta. The parasite infests and eats the lining of fish intestines.

The new test, developed by researchers at Oregon State University, uses DNA sequencing to identify the parasite within hours. It can be used to find the parasite in fish or in the water.

"This will allow us to go to places and see if it is present in the water, show us hot spots, and determine if the parasite is in tributaries," said Jerri Bartholomew, assistant professor of microbiology.

The parasite is found only in the Northwest, developing in small worms that live in the Deschutes, Willamette, Columbia and Klamath rivers before being released into the water. The parasite then enters fish through the skin. It takes relatively few of the organisms to kill salmon.

Researchers suspect the parasite is limited to certain types of rivers because the inital worm host has very specific habitat requirements.

Many fish seem to have resistance, but chinook salmon in the Klamath River "for some reason are being affected more now," Bartholomew said. "It may also be that parasite levels are higher than in the past."

Scientists say parasites and disease are responsible for low salmon returns in the Klamath River - this year in particular. Poor water quality and overfishing are also blamed.

Declines in salmon returns prompted Congress to begin a recovery effort in 1986, leading to increased research that uncovered diseases in the fish.

Samples taken from fish also show that as many as 80 percent of young Klamath chinook are infested with a different parasite by the time they reach the ocean. The other parasite does not appear to kill the fish but it weakens salmon by making their kidneys less efficient at filtering their blood.


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