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.

Authors: 
R. Adam Ray et al
Short Description: 
The authors present a model for ceratomyxosis-induced mortality in Oncorhynchus tshawytscha, from which parameters important to the persistence of Ceratomyxa shasta are identified.
Product Number: 
ORESU-R-10-031
Entry Date: 
Monday, June 24, 2013
Length: 
8 pp.
Miscellaneous: 
Additional authors: Rhilippe A. Rossignol and Jerri L. Bartholomew
Source (Journal Article): 
Diseases of Aquatic Organisms 93:63-70
DOI Number (Journal Article): 
10.3354/dao02281
Year of Publication: 
2010