Ceratonova shasta Prevalence of Infection in Klamath River Juvenile Chinook Salmon

The removal of multiple dams on the Klamath River made 2024 a unique year; a total of 1197 juvenile Klamath River Chinook Salmon (Oncorhynchus tshawytscha) collected between March and August 2024 were assayed for Ceratonova shasta by quantitative polymerase chain reaction (QPCR). Initial detection occurred on April 23, with the highest proportion of “disease- rated” salmon (37%) collected in the Shasta R. to Scott R. reach. Fall Creek hatchery salmon (coded wire tag fish) had a 73% prevalence of infection, with disease detection occurring within a week of their May releases. Gill tissue testing showed no prognostic advantage over intestinal tissue, as the initial detection date was the same for both tissues. Dam removal operations altered river flow, temperature, and turbidity compared to previous years. Higher river temperatures in March and April likely influenced the earlier occurrence of actinospores and resulting fish infections. This season, the historical prevalence of infection (64%) was similar to what was reported for 2023 (62%).