Colorado’s rainbow trout population once again breeding in the wild |

Colorado’s rainbow trout population once again breeding in the wild

Dave Parri, a guide and avid angler from Hot Sulphur Springs, holds a wild rainbow he caught last winter on the upper Colorado River.
Courtesy Colorado Parks and Wildlife |

For the first time in about two decades, rainbow trout are successfully reproducing in Colorado’s waters.

Colorado Parks and Wildlife fisheries biologist Jon Ewert said after years of strategic stocking, he recently has seen wild-hatched rainbows in Summit County’s Blue River, especially north of Green Mountain Reservoir.

“It’s exciting because there were many, many years there — 20 years or more — where that did not happen,” he said. “You could look and look and look, and there was no such thing as a juvenile rainbow trout anywhere.”

Rainbows are a desirable sportfish and preferred by many anglers because they are easier to hook and put up a stronger fight than brown trout. Rainbow trout are distinguished by dark spots and a reddish horizontal stripe that travels down a light-colored body.

“The rainbow trout is extremely important, and it’s vital to good fishing in Colorado,” said Randy Ford, owner of Alpine Fishing Adventures.

He said the fish are the best targets for tourists, children and beginners, and rainbows help sustain populations of other fish more popular with experienced anglers.

Fishing brings $1.9 billion in direct and indirect economic contributions and 16,000 jobs in the state, according to a 2015 CPW report, and residents and visitors spent more than 26 million days fishing in 2014.

Nick McDonnell, shop guy and guide with Colorado Angler, said before, his company would catch one rainbow for every 10 brown trout. Now, guides are seeing more rainbows on the Colorado and Arkansas rivers, and they’re larger in size.

The company caught five or six rainbows on the Colorado River on Wednesday that were 14 to 16 inches long, he said. “To get a rainbow on the Colorado is pretty cool to us just because we don’t see them very often.”


After the sportfish was devastated by whirling disease in the 1990s, CPW announced in June that rainbow trout populations are increasing in most major rivers in the state thanks to the two-decade effort by the agency’s aquatic scientists and biologists.

Since last summer, anglers have reported that they are catching nice size rainbows in the upper Colorado, Rio Grande, upper Gunnison, Poudre, East, Taylor, Arkansas and Yampa rivers and others.

In the U.S., rainbow trout are native to the coasts of the Pacific Northwest. The fish was introduced in Colorado, and around the world, in the 1880s and became a mainstay of the state’s hatchery system.

The whirling disease problem started in 1986 when a private hatchery unknowingly imported infected rainbow trout from Idaho that were stocked in 40 different waters in Colorado. The disease infected CPW hatcheries and spread throughout the state.

Whirling disease is caused by a spore that infects the spine of very young fish. The infection deforms the spine causing the fish to swim in a whirling pattern and then die.

The disease hit Colorado’s rivers and natural reproduction of the species ended in Colorado’s rivers, which allowed the immune brown trout to become the dominant sport fish for the past 15 years.

By the mid 1990s, rivers in Colorado and other western states were thoroughly infected.

At a national conference on whirling disease in Denver in 2002, a German researcher presented information that showed trout at a hatchery in Germany, operated by a family named Hofer, were resistant to the parasite.

Colorado’s aquatic staff imported eggs from Germany and hatched them at the University of California at Davis. The fingerlings were then brought to CPW’s Bellvue hatchery near Fort Collins.

By 2006 Schisler stocked some of the Hofer trout species in two reservoirs west of Berthoud. Anglers reported that the fish hit hooks hard and were easy to catch. This made them ideal for stocking in reservoirs where anglers expect to catch fish.

However, this trout species didn’t possess a flight response to danger because they had been domesticated in a hatchery for generations. They wouldn’t survive predation and fluctuating water conditions in creeks and rivers.


CPW researchers started cross-breeding the Hofers with existing strains of rainbow trout that possessed wild characteristics and had been stocked in rivers for years.

After three years, some of the crosses were ready for stocking with the hope that the fish would survive, reproduce and revive a wild, self-sustaining population of rainbows. Biologists first stocked 5-inch Hofer-crosses, but they didn’t survive. type of rainbows

Then in 2010, the cross fingerlings were stocked in the Colorado River near Hot Sulphur Springs. When researchers returned to survey the area 14 months later, they found good numbers of 15-inch rainbows and evidence that young fish were hatching in the wild.

CPW biologists have been stocking fingerling Hofer-crosses throughout the state since then at different sizes and times of year to optimize survival. The young fish are surviving, and the agency is confident that Colorado’s rivers and streams are again home to wild rainbows.

The Hofers are also providing other benefits to CPW and Colorado’s anglers.

Because the fish grow much faster than standard rainbow strains, state hatcheries can raise more fish in a shorter amount of time. They can also be crossed with other trout strains and are well suited to reservoirs where they don’t reproduce naturally but are ideal for still-water anglers.

“We’re moving back toward the time when some of our rainbow trout fisheries and rivers will be self-sustaining again,” he said. “We’re hoping to reach a point where we don’t need to stock rainbows into the Colorado River and the Blue.”

Ewert wants to establish rainbow trout spawning runs up waterways that feed Dillon Reservoir and plans to stock roughly 50,000 fingerling rainbows in Tenmile Creek this month in hopes that the fish will find their way to the reservoir, mature and then return to the Tenmile to reproduce.

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