Infection of Juvenile Salmonids by Salmincola californiensis (Copepoda: Lernaeopodidae) in Reservoirs and Streams of the Willamette River Basin, Oregon

AbstractWe assessed infection prevalence and intensity by the ectoparasitic copepod Salmincola californiensis among salmonid species rearing in reservoirs and streams upstream of reservoirs in the Willamette River basin, Oregon, during 2012 and 2013. Infection levels of juvenile Chinook Salmon Oncorhynchus tshawytscha, Rainbow Trout O. mykiss, and Cutthroat Trout O. clarkii were greater in reservoirs than in streams and increased with the age and size of fish. Copepods were more likely to be attached within the brachial cavity of reservoir fish (79%), whereas fins were the most common attachment site on stream fish (71%). Chinook Salmon in reservoirs were more vulnerable to infection than other species. Age-0 Chinook Salmon in reservoirs showed increasing infection prevalence throughout the year, reaching 84% by fall (compared with 11% in streams). Infection intensity was greater for age-0 Chinook Salmon in reservoirs than for those in streams. Infection prevalence for reservoir-rearing Rainbow Trout was ...