Abstract - Stocking et al. 2006

Stocking, R. W., Holt, R. A., Foott, J. S. and Bartholomew, J. L. (2006)
Spatial and Temporal Occurrence of the Salmonid Parasite Ceratomyxa shasta (Myxozoa) in the Oregon-California Klamath River Basin.
Journal of Aquatic Animal Health.Vol:18
Ceratomyxa shasta has been implicated as a significant source of salmonid mortality in the Lower Klamath River (below Iron Gate dam, a barrier to fish passage). A study on the prevalence of C. shasta and its geographic and spatial distribution throughout the Klamath River basin was conducted to determine when and where juvenile salmon encounter lethal parasite doses. Ceratomyxa shasta susceptible rainbow trout (Oncorhynchus mykiss) were exposed to the parasite in the Klamath River and held for 4 d at seven locations between Beaver Creek and Keno Reservoir in April, June, July, September, and November 2003. A Klamath River strain of fall Chinook salmon (O. tshawytscha) was held in three locations in the Upper Klamath River in April, June and July. In June 2004, rainbow trout exposures were conducted for 4 d at 18 locations between Upper Klamath Lake and the mouth of the Klamath River, including several major spawning tributaries, with one fall Chinook exposure occurring in the Lower Klamath River. Rainbow trout mortality due to infection for groups exposed in the Upper Klamath River was reduced (<8.0 %) and delayed (mean day to death 40-110 d) compared to mortality in groups exposed in the Lower Klamath River (>98%, mean day to death 33-36 d). Fall Chinook salmon did not become infected in the Upper Klamath River but sustained near 50% mortality in the Lower Klamath River. Examination of the data implicates infectious dose as the most likely cause of the dramatic differences in infection severity between the Upper and Lower Klamath River as differences in water temperatures during exposure were not significant enough to explain the disparity. It also appears that the parasite life cycle is largely confined to the main-stem Klamath River suggesting that the invertebrate host is also confined to this area.
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