Graduate Thesis Or Dissertation
 

Occurrence of the protozoan parasite Ceratomyxa shasta among salmonid fishes in Oregon waters

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  • This project was initiated to determine the incidence, distribution and species of fish affected by Ceratomyxa shasta in Oregon waters. Returning adult Pacific salmon and steelhead trout were chosen for the survey because they were known to be susceptible to infection. The parasite was also believed to be an important cause of prespawning losses. All coho salmon samples obtained from the Columbia River basin contained individuals infected with Ceratomyxa shasta. The infection was greatest at the Bonneville and Sandy hatcheries, where approximately 75 percent of the fish examined were infected. The only coastal sample found to contain coho salmon infected with Ceratomyxa shasta was taken from the Nehalem River. Fish that reached the hatchery but died before the start of spawning operations were obtained from the Klaskanine and Sandy hatcheries. The incidence of Certaomyxa shasta infected fish in these samples was in both cases greater than in samples obtained during spawning. Spring chinook obtained from coastal river locations (Trask and Rock Creek hatcheries) were not infected with this parasite. Infected spring chinook were found in all Willamette River tributaries surveyed. The incidence was greatest (28 percent at Dexter Dam) in fish which had migrated the farthest distance up the river. Ceratomyxa shasta in dead fish obtained from the Dexter Dam holding pond was over twice that found in spawned fish from this location. The incidence and distribution of Ceratomyxa shasta in fall chinook salmon was different from that found in coho or spring chinook. The coastal sample obtained from the Trask Hatchery contained one infected individual. The Klaskanine River was the only tributary on the lower Columbia that contained infected fall chinook, eight percent of these fish were infected. The infection was much greater in fall chinook sampled at the Oxbow Hatchery (Snake River) than in fish obtained from sites on the lower Columbia River. Sixty-five percent (65%) of the fish from this hatchery were infected. The incidence of Ceratomyxa shasta in prespawning mortalities at the Oxbow Hatchery (Snake River) was identical to that found in adults killed at spawning. Samples of steelhead trout obtained from the Big Creek Hatchery and Pelton Dam contained fish infected with this disease. The number of spores per smear of infected steelhead tissue was low when compared to the number observed in smears from coho and spring chinook. No steelhead mortalities were obtained. The incidence of Ceratomyxa shasta in adult salmonids does not appear to be related to the sex of the animals. The disease incidence appears to be related to the distance and rate of migration. Infections in adult salmonids caused by Ceratomyxa shasta probably occur during the freshwater phase of their life cycle. Geographically, Ceratomyxa shasta is widely distributed throughout the survey area. The parasite was found in all areas of the Columbia River basin sampled. Coastal river systems found to contain infected fish were the Nehalem and possibly the Trask. The incidence of Ceratomyxa shasta in coastal rivers decreased progressively from the Columbia River southward.
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