DOW reports good news for fishermen of Colorado’s rivers

Disease resistant fish

In an exciting development for anglers and river enthusiasts, Colorado Division of Wildlife (DOW) fish biologists believe they are close to developing whirling disease-resistant rainbow trout that can reproduce in the wild.




DOW scientists confirmed that the fish they caught in the Gunnison and Frying Pan rivers were the offspring of whirling disease-resistant trout that were stocked in 2004. "What we’re basically able to show in two different places is we have the resistant species," said DOW aquatic researcher Barry Nehring.
Fellow aquatic research scientist George Schisler said the DOW should know within a year whether the fish can reproduce in the wild. "We’re really getting close to coming full circle," he said.
Whirling disease decimated most of Colorado’s naturally producing rainbow trout populations over a decade ago. DOW scientists said success will translate into the reestablishment of a self-sustaining wild Colorado rainbow trout population.
"Ultimately we’ll be able to restore the disease-resistant rainbow to the natural environment," said Schisler.
Biologists have long been frustrated with the whirling disease parasite, which deforms the fish’s cartilage, causing it to swim in circles. The parasite can attack all species of trout, but some species, like the brown, are resistant to it. The new rainbow hybrid, which is a cross between a Hofer and a Colorado rainbow, appears to deter the parasite as well. "All indications are they have picked up some resistance," said Schisler, of the hybrid.
The hybrid was developed in collaboration with German scientists who were able to locate disease-resistant farm-bred rainbow trout from the private Hofer hatchery.
Schisler says whirling disease developed more than a century ago among trout in Europe, where it flourished in fishponds. Rainbow, though native to tributaries of the Pacific Ocean in the United States and Asia, was introduced to Europe in the 1800s, where it now exists mainly as a farm fish. Whirling disease was introduced from Europe into U.S. trout populations in the 1950s.

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