Colorado biologists are on a breeding blitz to revive the species ravaged by whirling disease. Super-resilient trout found in the Gunnison River will be stocked this spring with the hope of creating a self-sustaining population, says Bruce Finely of the Denver Post
Volunteers snipped off the left pelvic fin from the belly of each trout. Then they plopped them back into tanks, 20,000 fish in two intense workdays last week. Rainbow trout are non-native fish, introduced during Colorado’s 19th century. The fin snipping is to mark rainbows from a newly discovered resilient subgroup will allow tracking when releasing them into the Arkansas River this spring.
This will help them determine the success of this group of whirling disease-resistant trout. It is the latest step as CPW runs with a scientific breakthrough that could lead to defeating whirling disease. Like rainbow trout, the disease is imported. A parasite invader hitched a ride to Pennsylvania from Europe in 1958 on a frozen fillet and has been attacking the soft cartilage of fingerling rainbows ever since, causing them to grow into deformed, c-shaped juveniles. They swim in circles and die of starvation or exhaustion.
Now, this new breed of rainbows could make a comeback four years ago, a researcher investigating rainbow genetics spotted an isolated group at the bottom of a rocky chasm in the Black Canyon of the Gunnison River. These rainbow trout seemed able to withstand whirling disease. State biologists verified the immunity and began a genetic analysis.
The whirling disease parasite that had infected fisheries in Pennsylvania and other Eastern states reached Colorado in 1980. It took hold inside this fish hatchery along the Arkansas River with devastating effects. Whirling disease parasites spread with river water into hatchery pipes and tanks, contaminating state fish-breeding operations. When rainbow trout were distributed statewide for stocking, so was whirling disease. The result was the near-total ruin of rainbow trout. Whirling disease also threatens other fish, including the native greenback cutthroats.
Last year, state biologists tossed some of their captive-bred rainbows into the Arkansas River. While acid metals contamination from inactive mountainside mines still impairs headwaters, state data show, the river flows around Salida are diluted enough that brown trout are multiplying. The biologists used an electro-fishing survey method to check up on those resilient rainbows, marked for tracking. They determined that the fish were surviving.