October 12, 2006

Whirling disease resistant trout planted in two Utah waters

Rainbow trout that have shown a resistance to whirling disease were stocked into Hyrum and Porcupine reservoirs in May, and now the fish are big enough to catch.

The Utah Division of Wildlife Resources (DWR) needs the help of anglers to learn how well these fish survive and grow, and how their fighting ability compares with rainbow trout that are already in Utah.

So far, biologists at the DWR's Fisheries Experiment Station in Logan have been happy with the growth rates of the whirling disease resistant trout. Biologists say their growth rates are superior to the rates of a Utah hatchery strain of rainbows called TenSleep.

Rainbow strain shows promise

The whirling disease resistant rainbow trout strain is a cross between two strains - the Harrison Lake strain and the Hofer strain.

The Harrison Lake strain comes from Harrison Lake, Montana, which received rainbows from Lake DeSmet in Wyoming in 1981. Work by Richard Vincent with the Montana Department of Fish, Wildlife and Parks indicates these fish may have some resistance to whirling disease.

DWR biologists at the Fisheries Experiment Station conducted more research and found that Vincent was right - even after exposure to high doses of the whirling disease parasite, a high proportion of this wild strain was not infected with whirling disease or had significantly lower numbers of whirling disease spores in them.

Researchers have also done work with the Hofer strain, and they've found the Hofer strain is even more resistant to whirling disease than the Harrison strain is.

The Hofer strain was derived from rainbow trout that were shipped from Colorado to Germany in the 1880s. After more than a century of exposure to the whirling disease parasite in Germany, a fast growing, domesticated, whirling-disease resistant strain evolved.

Some of these fish were then imported back to the United States by researchers at UC Davis in California and the Colorado Division of Wildlife.

Trout planted in May

The Colorado Division of Wildlife has provided the Utah Division of Wildlife Resources with eggs that are a cross of the Harrison and Hofer rainbows. DWR biologists are using these eggs to develop a broodstock in Utah. They're also conducting studies to see how well these fish do in the hatchery and in the wild.

In May, the whirling disease-resistant strain of rainbows and the TenSleep strain were stocked as fingerlings in Hyrum and Porcupine reservoirs in northern Utah.

Anglers who catch the fish can tell the difference by looking at which pelvic fin is missing. If the right fin is gone, the fish is from the whirling disease resistant strain. If the left fin is gone, the fish is from the TenSleep strain. Fish that have not had a pelvic fin removed by biologists are not part of the study.

Anglers: biologists need your help

The DWR needs the help of anglers to conduct its study. Biologists want to know how many fish anglers catch and keep from each strain, and how many fish anglers catch and release from each strain. A wooden box with cards anglers can fill out is available at the Hyrum State Park fish cleaning station located by the boat ramp. Anglers are asked to fill the cards out and deposit them in the box.

Anglers can also call the Fisheries Experiment Station at (435) 752-1066 ext. 22 to pass data along or to get more information about the study.

The biologists also welcome information about the fish's size, its fighting ability (or other sport fishing characteristics) and any deformities.

The Whirling Disease Foundation has provided a grant to help cover the costs of the study.

"Biologists hope the disease-resistant fish perform well," says Eric Wagner, director of research at the DWR's Fisheries Experiment Station. "If they do, they'll help reduce parasite numbers in wild and stocked fish, and prevent further spread of the disease."