Posted: Monday, January 12, 2004 10:00 pm
CORVALLIS - Scientists at Oregon State University have solved the mystery of why so many fish in the Newberg Pool of the Willamette River have deformed bones.
"I think we have the answer," Larry Curtis, one of the lead researchers, said today.
The fish are deformed because of a couple of parasites that infest their bones - not because of pesticides or other pollutants - the study has shown.
The findings confirm preliminary results reported a year ago.
The study was the result of prodding by then-Sen. Mae Yih, D-Albany, who pressed the Legislature in 2001 to approving funding to get an answer to the long-standing issue of fish deformities in the Willamette River.
The state Watershed Enhancement Board funded the study with nearly $500,000. The board got an update on the finding last month, and the university publicized the results in an anouncement today.
Some work on the study remains to be finished. A scientific paper identifying the cause of the deformities has been submitted for publication to the Journal of Aquatic Animal Health, a publication of the American Fishery Society.
Curtis, head of the OSU Department of Environmental and Molecular Toxicology, said he would forward the results to Yih because of her role in getting the study launched.
Curtis said fish were sampled mainly at three spots on the Willamette: at Corvallis, near the Wheatland Ferry below Salem, and in the Newberg Pool, a slow-moving reach of the river between Newberg and Oregon City.
Several studies over the last 20 years had noticed an unusual concentration of skeleteal deformities in fish from the Newberg Pool.
"At this point it's clear that virtually all of these deformities are being caused by two parasites, and we've demonstrated in laboratory studies how the deformities occur," Curtis was quoted in the university's press statement. "The parasites, which for some reason are more prevalent in this part of the river, pose little threat to human health, and they are destroyed either by freezing or cooking of infected fish."
OSU said the three-year study included a team of fisheries experts, microbiologists, environmental chemists and toxicologists from the OSU Agricultural Experiment Station.
Co-authors included Michael Kent, director of the Center for Fish Disease Research at OSU, and Douglas Markle, a professor of fisheries and wildlife.
The university provided these additional details:
Two species of minnow, the chisel mouth chub and northern pike minnow, have most often suffered skeletal deformities, researchers found. The study revealed that most of the deformities are caused by a fluke, Apophallus donicus, which at various life stages passes through snails, fish, and fish-eating birds or mammals, and in one stage is a very tiny worm that can infect fish. A lesser number of fish are affected by a myxozoan similar to Myxobolus cyprini.
In fish, the flukes can penetrate to the bone, form a shell or "cyst," and in the process cause spinal deformities and unusual bone growth. They can be lethal, especially in very young fish.
The Myxozoan is a relative of the parasite that causes whirling disease in salmon, and is apparently native to the Pacific Northwest. Bone deformities that resemble those caused by this parasite have been identified in museum specimens from the 1850s.
"There's some evidence that the levels of these parasites increased in the 1950s, but it's not definitive," Markle said. "It's also not clear just what environmental conditions in the Newberg Pool favor higher levels of the parasites. But the deformities they can cause are now very clear. Some fish that are born in the middle of the spawning season when fluke levels are highest have almost a 100 percent incidence of infection and deformities."
According to Kent, the fluke parasite could, in theory, infect people as well if they ate raw fish. Pets also be vulnerable. But in humans the parasite would only cause gastrointestinal upset, he said, and in any case any problems can be prevented by either freezing or cooking of infected fish. Consumption of fresh raw fish from the Willamette River is not advisable, he said.
Exhaustive research on other possible causes of this problem showed no other concerns, Curtis said. In comparing water from the Newberg Pool to other sites, the study found no significant difference in levels of heavy metals, dioxins, or other "legacy" pollutants from the past such as DDT or PCBs, he said, all of which were present but at extremely low levels. The data has not yet been finalized on organophosphates.
"The Willamette is a big river and there's a lot of water moving through it," Curtis said. "There actually is a huge dilution factor that tends to give most lower parts of the river very similar levels of water quality, other than a superfund site in Portland harbor."
Research will continue in efforts to determine why the Newberg Pool has higher levels of these parasites and the deformities they cause, the scientists said.