Density of the Waterborne Parasite Ceratomyxa shasta and Its Biological Effects on Salmon

Abstract

The myxozoan parasite Ceratomyxa shasta is a significant pathogen of juvenile salmonids in the Pacific Northwest of North America and is limiting recovery of Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon populations in the Klamath River. We conducted a 5-year monitoring program that comprised concurrent sentinel fish exposures and water sampling across 212 river kilometers of the Klamath River. We used percent mortality and degree-days to death to measure disease severity in fish. We analyzed water samples using quantitative PCR and Sanger sequencing, to determine total parasite density and relative abundance of C. shasta genotypes, which differ in their pathogenicity to salmonids. We detected the parasite throughout the study zone, but parasite density and genetic composition fluctuated spatially and temporally. Chinook and coho mortality increased with density of their specific parasite genotype, but mortality-density thresholds and time to death differed. A lethality threshold of 40% mortality was reached with 10 spores liter ؊1 for Chinook but only 5 spores liter ؊1 for coho. Parasite density did not affect degree-days to death for Chinook but was negatively correlated for coho, and there was wider variation among coho individuals. These differences likely reflect the different life histories and genetic heterogeneity of the salmon populations. Direct quantification of the density of host-specific parasite genotypes in water samples offers a management tool for predicting host population-level impacts.

Modeling the Effects of Climate Change on Disease Severity: A Case Study of Ceratonova (syn Ceratomyxa) shasta in the Klamath River

“…Together, these models predict the probability that polychaetes will occupy specific locations based on maximum winter discharge predicted for each of the modeled future climate scenarios. 2DHMs have been developed for three sections of the Klamath River (Wright et al 2014) in which prevalence and severity of C. shasta infection is high in juvenile salmon (Hallett and Bartholomew 2006;Hallett et al 2012). The logistic regression model developed by Alexander et al (unpub.…”

Science Advancements Key to Increasing Management Value of Life Stage Monitoring Networks for Endangered Sacramento River Winter-Run Chinook Salmon in California

“…Notably, pathogens caused a high level of pre-spawn mortality (27%) for the SRWRC broodstock at the LSNFH in 2015 (Voss and True 2016). In the Klamath River, where water project operations influence disease outbreaks linked to salmon mortality, extensive monitoring of C. shasta and P. minibicornis is routine (Hallett et al 2012;Ray et al 2012Ray et al , 2014. C. shasta is a progressive disease, and fish along the monitoring network need to be evaluated over time because early-stage infections could progress to a diseased state over time True et al 2013).…”

Annelid-Myxosporean Interactions

“…For instance, C. shasta genotypes are linked with different susceptibilities to infection amongst fish species and strains (Atkinson and Bartholomew 2010; Hallett et al 2012). The question of whether these C. shasta genotypes are linked to differential susceptibilities to infection amongst M. speciosa strains has yet to be addressed.…”