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U.S. trout population declining from whirling disease
November 10, 1997
Web posted at: 2:09 p.m. EST (1909 GMT)BOZEMAN, Montana (CNN) -- A disease that disorients fish, eventually killing them, is spreading across the United States, affecting not only the fish but the people who depend on them for their livelihood.
Scientists say whirling disease, a condition that causes fish to constantly spin in circles, is caused by parasites. It apparently came from Europe to the United States in the 1950s and has since spread to 22 states.
Since Beth MacConnell first discovered the disease in Montana, there has been a 94 percent decline of rainbow trout in the Madison River. The brown trout population has also been infected but shows relatively low mortality rates.
"They're whirling because the parasite has destroyed the cartilage at the base of their brain," MacConnell explained, "so basically their balance is gone and you might see them whirl in one direction, or they can corkscrew."
Young trout are often killed by severe whirling disease infections. The older ones, left to spin in the water, have difficulty feeding or avoiding predators.
The good news is that whirling disease, while deadly to fish, doesn't affect people. The bad news is that when a single infected fish dies, many thousands to millions of the parasite spores are released into the water. And the parasite that causes it, Myxobolus cerebralis, is so far nearly indestructible and has an indefinite lifespan.
"The parasite that comes out of the fish can live outside of the fish, in the environment, for 20 years. You could put the fish back in and they could still get infected," MacConnell said.
Fishermen have been warned that even the mud on their boots can carry the parasite. There are now restrictions on moving fish out of state.
It is a fisherman's nightmare.
"Fishing in Montana is more than a $250-million-a-year industry, and in a small populated state like ours, that is a large portion," said Tom Anacker, the president of the Whirling Disease Foundation.
Anacker, who says he learned to fly fish from his father, said the rainbow trout's decline would also hurt the Madison River's reputation as a recreational area.
"This is a famous river and it's one of national treasures as far as the fly fishing world goes," he said.
Research is under way to find a cure for whirling disease. But until researchers learn how to control it, it will remain a major threat to a favorite pastime, and at least one state's biggest industry.
Correspondent Sharon Collins contributed to this report.
Related sites:
Note: Pages will open in a new browser window
- The Whirling Disease Foundation
- What in the Whirld: An illustrated guide to whirling disease - from Montana Fish, Wildlife & Parks
- The Facts of Whirling Disease - from Outdoors Online
External sites are not endorsed by CNN Interactive.
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