DAO 93:63-70 (2010)  -  DOI: https://doi.org/10.3354/dao02281

Mortality threshold for juvenile Chinook salmon Oncorhynchus tshawytscha in an epidemiological model of Ceratomyxa shasta

R. Adam Ray1,2, Philippe A. Rossignol1, Jerri L. Bartholomew2,*

1Department of Fisheries and Wildlife, Nash Hall, Oregon State University, Corvallis, Oregon 97331, USA
2Department of Microbiology, Nash Hall, Oregon State University, Corvallis, Oregon 97331, USA
*Corresponding author. Email:

ABSTRACT: The myxozoan parasite Ceratomyxa shasta is a significant pathogen of juvenile Chinook salmon Oncorhynchus tshawytscha in the Klamath River, California, USA. This parasite requires 2 hosts to complete its life cycle: a freshwater polychaete (Manayunkia speciosa) and a salmonid. The complex life cycle and large geographic area where infection occurs make it difficult to monitor and manage ceratomyxosis. We present a model for ceratomyxosis-induced mortality in O. tshawytscha, from which parameters important to the persistence of C. shasta are identified. We also experimentally quantify specific parameters from the model and identify a mortality threshold (a critical parameter), by naturally exposing native O. tshawytscha to C. shasta in the Klamath River. The average percent mortality that resulted from these experimental challenges ranged from 2.5 to 98.5% over an exposure dose of 4.4 to 612 × 106 parasites. This experiment identified a non-linear mortality threshold of 7.7 ± 2.1 × 104 actinospores fish–1 for Chinook salmon from the Iron Gate Hatchery on the Klamath River. Below this threshold no mortality occurred and above it mortality increased dramatically, thus providing a target by which to reduce parasitism in emigrating juvenile O. tshawytscha.


KEY WORDS: Ceratomyxa shasta · Epidemiological model · Mortality threshold · Chinook salmon · Disease ecology · Myxozoan · Macroparasite


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Cite this article as: Ray RA, Rossignol PA, Bartholomew JL (2010) Mortality threshold for juvenile Chinook salmon Oncorhynchus tshawytscha in an epidemiological model of Ceratomyxa shasta. Dis Aquat Org 93:63-70. https://doi.org/10.3354/dao02281

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