DENVER—A crossbred trout that appears to be resistant to whirling disease has reproduced in the wild, raising hopes that rainbow trout can be re-established in areas where the disease wiped out the fish.
A cross of the Hofer rainbow trout and other rainbow strains has reproduced in the Gunnison River and in ponds along the Frying Pan River near Basalt.
“They were plump, colorful fish, they looked good,” said Barry Nehring, an aquatic researcher for the Colorado Division of Wildlife in Montrose “This is indicative that we’ve had successful reproduction.”
The Division of Wildlife is trying to rebuild rainbow populations with trout resistant to whirling disease, a parasite that deforms and kills young fish.
The disease was confirmed in Colorado in the late 1980s and spread to most of the state’s major river drainages after infected fish from a private Idaho hatchery were released. It also infiltrated state hatcheries.
By the early 1990s, rainbow populations collapsed, disappearing entirely from some rivers and lakes. Only a few remnant populations held on.
In 2003, state researchers worked with the University of California at Davis to import eggs of a rainbow trout thought to be resistant to whirling disease. They started a brood stock and crossed Hofer rainbow trout with other strains, which they released into the Gunnison and Colorado rivers and the ponds along the Frying Pan River.
Genetic testing confirmed that fish captured in October were offspring of the Hofer-cross rainbows stocked in 2004 and 2005.
George Schisler, a Division of Wildlife aquatic researcher, said the next milestone could come late this year.
“The fish need to make it to age one and beyond, so we’ll see this fall,” Schisler said.
State fish hatcheries are expanding production of the various crosses. The division plans to stock more than 1 million of the crossbred fish in lakes and rivers throughout Colorado.
