Myxobolus cerebralis, a myxozoan parasite of salmonids, is the causative
agent of whirling disease. The parasite is considered widespread throughout
northeastern Oregon in the Grande Ronde and Imnaha River basins where
threatened and endangered salmonid populations exist. The work presented in this
thesis comprises several studies that assess the effects of M. cerebralis on resident
and anadromous salmonids in Oregon.
Laboratory challenges to determine the susceptibility of indigenous
Deschutes River, Oregon, salmonids to M. cerebralis were conducted as part of a
study to assess the risk of reintroducing anadromous salmon above a migration
barrier on that river. This study was the first to assess the susceptibility of kokanee
salmon Oncorhynchus nerka to M. cerebralis, and results contribute to the
understanding of salmonid susceptibility as it relates to species and age. Further,
this study demonstrates that the indigenous salmonids present in the river are
susceptible to infection, but resident rainbow trout Oncorhynchus mykiss would be
most at risk should introduction of M. cerebralis occur in this system.
The susceptibility of chinook salmon Oncorhynchus tshawytscha to M.
cerebralis was assessed following laboratory challenges at different ages to
different parasite levels. Results from this study indicate that chinook salmon are
more resistant to M. cerebralis infection than susceptible rainbow trout; resistance
to disease developed in chinook salmon exposed after 3 weeks of age. Sustained
exposures to a low parasite dose were performed to model the conditions chinook
salmon would encounter in a natural exposure. Following continuous exposure to
low parasite densities, chinook salmon were very resistant to infection and disease.
Managed populations of chinook salmon and steelhead Oncorhynchus
mykiss juveniles are held in acclimation facilities on their natal streams before
release to commence their seaward migration. Rainbow trout fry were held at each
of the acclimation facilities to detect the presence of M. cerebralis and to assess the
prevalence of exposure during the acclimation period. Results from these exposures
indicate that the Wallowa acclimation facility is a high-risk site for parasite
exposure of steelhead juveniles. Further, detection was confirmed in several rivers
and streams where the presence of M. cerebralis has been suggested.
Finally, a preliminary study on the effect of M. cerebralis on survival of
steelhead juveniles upon transfer to saltwater was conducted. Results from this
study indicate that M. cerebralis exposure and infection may increase mortality
among juvenile steelhead during saltwater adaptation. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31686 |
| Date | 27 September 2002 |
| Creators | Sollid, Sarah A. |
| Contributors | Bartholomew, Jerri L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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