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Diseases of Aquatic Organisms

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DAO 62:85-92 (2004)  -  doi:10.3354/dao062085

Monitoring Ceratomyxa shasta infection during a hatchery rearing cycle: comparison of molecular, serological and histological methods

Jerri L. Bartholomew1,2,*, E. Ray4, B. Torell5, M. J. Whipple4, J. R. Heidel2,3

1Department of Microbiology, Oregon State University, 220 Nash Hall, 2Center for Fish Disease Research, Oregon State University, 220 Nash Hall, and 3College of Veterinary Medicine, Oregon State University, 134 Magruder Hall, Corvallis, Oregon 97331-3804, USA
4Washington Department of Fish and Wildlife, 1111 Washington Street SE, Olympia, Washington 98504, USA
5911 Jefferson Street, Oregon City, Oregon 97045, USA

ABSTRACT: The prevalence of Ceratomyxa shasta infection in production stocks of steelhead Oncorhynchus mykiss and cutthroat trout O. clarki was monitored using a parasite-specific polymerase chain reaction (PCR) assay. For all 4 stocks of fish followed through their 1 yr rearing cycle, C. shasta infection was detected despite their genetic resistance to the disease and the treatment of the incoming water with ozone. Infection was confirmed using serological methods and standard histological procedures, except when prevalence was low (<10%). This suggests that at the lowest infection levels PCR is more sensitive than other methodologies, and can be used as an early indicator of infection. Results of the PCR assay continued to correlate with histological and serological detection as the numbers of parasites and the lesion severity increased over the rearing cycle. For both steelhead and cutthroat trout, early infections were characterized by large numbers of parasites on the epithelial surface, but with little associated inflammation. At release as yearlings, the infection prevalence in all stocks was greater than 90% and the inflammatory response in many fish was extensive, with tissue necrosis and mucosal damage. Although C. shasta infections no longer result in high mortality at this facility, results of this study indicate that the parasite remains a contributor to low condition indices in these fish, despite their genetic resistance and ozone disinfection of the water supply.

KEY WORDS: Ceratomyxa shasta · Salmonid disease · Myxozoan · Ozone · Disease resistance

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