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Diseases of Aquatic Organisms

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DAO 57:77-83 (2003)  -  doi:10.3354/dao057077

Efficacy of passive sand filtration in reducing exposure of salmonids to the actinospore of Myxobolus cerebralis

R. Barry Nehring1,*, Kevin G. Thompson1, Karen Taurman2, William Atkinson3

1Colorado Division of Wildlife, 2300 South Townsend Avenue, Montrose, Colorado 81401, USA
2Colorado Division of Wildlife, 317 West Prospect Street, Fort Collins, Colorado 80526, USA
3Colorado Division of Wildlife, 925 Weiss Drive, Steamboat Springs, Colorado 80477, USA

ABSTRACT: The aquatic oligochaete Tubifex tubifex parasitized by Myxobolus cerebralis releases triactinomyxon (TAM) actinospores that can infect some species of salmonids and cause salmonid whirling disease. Silica sand was tested as a filtration medium for removal of TAMs from water containing the parasite. Laboratory tests indicated sand filtration removed >99.99% of TAMs. In 2 different field tests, groups of 1 mo old rainbow trout Oncorhynchus mykiss were exposed for 2 wk to filtered and unfiltered water from a spring-fed pond enzootic for M. cerebralis. In November 2000, the exposure dose was estimated as between 3 and 5 TAMs fish-1. During a March 2001 exposure, the estimated dose was between 286 and 404 TAMs fish-1. Fish were held for 6 mo post exposure (p.e.) in laboratory aquaria for observation and evidence of clinical signs of whirling disease. We used 4 diagnostic techniques to assess the prevalence and severity of infection by M. cerebralis among fish exposed to filtered and unfiltered water. These included polymerase chain reaction (PCR) for genomic DNA of the parasite, histological evaluation for tissue damage, tissue digestion for quantification of cranial myxospores of the parasite, and total non-sampling mortality that occurred over 6 mo p.e. All diagnostic tests verified that the prevalence and severity of infection was significantly reduced among fish in treatment groups exposed to filtered water compared to those exposed to unfiltered water in both the low-dose and high-dose exposures.

KEY WORDS: Salmonid whirling disease · Myxobolus cerebralis · Sand filtration

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