Prevalence of Infection in Hatchery‐Origin Chinook Salmon Correlates with Abundance of Ceratonova shasta Spores: Implications for Management and Disease Risk

Abstract

AbstractCeratonova shasta is an endemic myxozoan parasite that impacts salmonid populations in the Klamath River (USA). High densities of C. shasta actinospores negatively affect the survival of migrating juvenile salmonids. Each year, approximately five million fall‐run Chinook Salmon Oncorhynchus tshawytscha smolts are released from a hatchery that is located below Iron Gate Dam, and they travel through an infectious zone where the densities of C. shasta spores are elevated and when disease risk is often highest. We examined several documented hypotheses regarding potential factors that contribute to the effects of C. shasta on salmonids in the Klamath River. Our results suggest that hatchery‐origin smolts may exacerbate the effects of the disease, as evidenced by an associative relationship between the prevalence of infection in out‐migrating hatchery fish with the densities of waterborne C. shasta spores in subsequent seasons (the following fall and spring). We found no evidence that the number of natural spawners, another potential contributor of spores, predicted peak spore density the following spring. Our findings warrant consideration in discussions of hatchery releases and management of flow regimes, and they identify avenues for future research to advance our understanding of how to reduce the adverse effects of C. shasta on salmonids in the Klamath River.