Juvenile Trout Study - Whirling Disease

2003 Summary

In September 2003, Utah State University Graduate Student Researcher Martin Koenig deployed sentinel cages containing juvenile Yellowstone cutthroat trout throughout the Teton River and selected tributaries in an effort to quantify whirling disease severity. Early in 2004, the Idaho Department of Fish and Game completed processing and testing of these test fish. Spore count results for this first trial of testing are now complete.

The table & chart below illustrates a comparison of percent infected with mean spore counts by location.Overall, the results indicate that whirling disease is indeed present throughout much of the valley, but may not be as severe as previously thought. Of the ten sites tested, eight showed positive for the parasite. All mainstem Teton River sites had fairly low rates of infection, along with low average spore counts. Fox Creek and Teton Creek (two important tributaries) showed higher rates of infection. However, only lower Teton Creek (“Steel Bridge”) showed significant average spore counts per fish.

Currently, samples from these 2003 series of tests are awaiting histological analysis, which uses microscopes to assess cranial tissue damage by the spores within affected fish. These samples will be examined and scored according to a severity index (ranging from 0 to 4) based on that of Baldwin (2000). Histological data combined with the above-mentioned spore count data will provide more informative results on the severity of whirling disease in the Teton Valley. A second round of sentinel testing should be completed to confirm these results and to collect data on locations not previously sampled.