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Colorado River is new home for whirling disease-resistant rainbow trout

Katie Looby/Sky-Hi Daily News
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About 80,000 whirling disease-resistant rainbow trout could re-establish the Colorado River fishery to its former diversity.

Colorado Division of Wildlife officials released 40,000 trout into the Colorado River at the Paul F. Gilbert State Wildlife Area on Tuesday and will release the remainder today.

“The hope is that these rainbow trout will grow and mature and start reproducing, and those young trout that are born are going to have this resistance to whirling disease,” says Jon Ewert, DOW fisheries biologist.



“What this represents is re-establishing the wild rainbow trout fishery that used to be here that was so spectacular 20 to 30 years ago. It’s kind of a new chapter.”

This is the first time rainbow trout resistant to whiling disease have been released in Colorado.



“We do stock rainbow trout from time to time,” he said. “That’s just basically to maintain some rainbow component to the fishery.”

Whirling disease deforms the spine in young fish, causing them to swim in circles or “whirl.” The disease is fatal to the fish.

A truck from Rifle Falls delivered 40,000 fish. It contained four tanks. Each contained 10,000 trout, and oxygen tanks injected oxygen into the water.

In the 1970s and ’80s the Colorado River was a trophy rainbow trout fishery, Ewert said.

“They were all wild, self-reproducing wild trout,” he said. “It could match up to any other rainbow trout fishery in the world.”

In 1987, whiling disease got into the river. Even though the rainbow trout could still lay eggs, the fry did not survive. People began to notice the shortage of small rainbow trout. The majority of the trout are now brown trout, because they are immune to whirling disease, according to Ewert.

In the 1880s Colorado swapped rainbow trout from the Gunnison River for German brown trout. A European researcher recently found that the rainbow trout living in a privately owned hatchery in Germany are immune to whirling disease. Those fish are descendants of the rainbow from Colorado, he said.

“We were able to get some of those eggs back,” he said. “It’s taken a lot of research and basically development … to come up with just the right genetics for what you think will be a good fish in the wild.”

The trout released into the Colorado River are five inches long. Fry have about a 10 percent chance of survival, but since these fish are more than three months old, their survival rate is higher.

In spring 2010 they should start spawning, Ewert said.

“It’s important to remember the spectacular quality of this fishery,” Ewert added. “It will continue to be a great fishery as long as we have enough water in the river.”


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