Whirling disease is caused by a naturally occurring parasite that passes through the fish’s skin. The organism attacks the cartilage of young fish and distorts the spine. The affected fish move in a whirling motion, basically swimming in circles when excited or trying to escape predation. This greatly reduces their ability to survive in the wild.

The disease was introduced to Colorado via a shipment of stocking fish from Idaho in 1986-87and discovered in state fish populations in 1994. Spread mainly via humans, it devastated most wild rainbow trout populations throughout the state.

However, Mark Jones, aquatic research leader for the Colorado Division of Wildlife, said Colorado leads the nation in the whirling disease war. “No other state has conducted more research into identifying real solutions to the whirling disease problem,” Jones said.

In addition to studying disease-resistant strains of fish, the DOW is looking at disease-resistant forms of the tubefix worm,, which carries whirling disease spores.

“Researchers have found some that are not hosts for the spores,” said Joe Lewandowski, with the Durango DOW. “We are looking at if we can grow them in areas where there is whirling disease and theycan outcompete the other tubefix worms.”

– Missy Votel