Susceptibility of select salmonids to Myxobolus cerebralis and effects of exposure on anadromous salmonids in Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hm50tv890

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  • 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.
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