Researchers: rainbow trout fishery could be on way back |

Researchers: rainbow trout fishery could be on way back

ASPEN – The results of an experimental breeding and stocking program have state wildlife researchers encouraged that Colorado’s rainbow trout fishery could be on the brink of a big comeback after being decimated by whirling disease.The Colorado Division of Wildlife is trying to rebuild rainbow populations with trout that are resistant to the parasitic spore that deforms and kills young fish.”There’s a lot of potential for re-establishing wild populations of rainbow trout,” state biologist George Schisler said.Next year, the Wildlife Division will start restocking lakes and streams with large numbers of rainbow trout that show strong resistance to whirling disease.Whirling disease is caused by parasite that penetrates the head and spinal cartilage of fingerling trout. The parasites multiply and affect equilibrium, causing the fish to swim erratically. It also affects feeding and the ability to avoid predators.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.Some rainbow populations in the mountains managed to avoid the worst of the disease in part because fast-running mountain streams don’t have the layer of mud on the bottom that’s ideal for worms that host the parasite.The parasite begins life as a spore capable of living in soil for 30 years. When an infected fish dies, the spores are released and attach to other fish or are eaten by bottom-dwelling worms. Fish also can be infected by eating the worms.Salmon and rainbow trout, native to the United States, are the most affected. Brown trout are more resistant to the parasite, possibly because they were exposed to it in their native Europe.In 2003, state biologists started crossing Colorado River rainbow trout with a resistant strain of trout from Germany. The crossbred fish were exposed to high doses of the parasite, and those that showed the greatest resistance were kept to breed the next generation.The Division of Wildlife is starting to raise large numbers of the resistant trout. About 20,000 of the fish have been stocked in the Gunnison River.Whirling disease, which isn’t a threat to humans, has been confirmed in 22 states.—Information from: The Aspen Times,

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