Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
CA-NV FHC: Fish Health Center Implementing New Molecular Tool
California-Nevada Offices , September 12, 2013
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Juvenile chinook salmon with coldwater disease.
Juvenile chinook salmon with coldwater disease. - Photo Credit: USFWS CA-NV Fish Health Center
Sample positive for Flavobacterium psychrophilum by QPCR.
Sample positive for Flavobacterium psychrophilum by QPCR. - Photo Credit: USFWS CA-NV Fish Health Center

By Anne Bolick

The California-Nevada Fish Health Center has recently implemented a molecular assay to rapidly detect bacterial coldwater disease (BCWD). Bacterial coldwater disease, caused by the gram-negative bacterium Flavobacterium psychrophilum, is responsible for significant losses of hatchery-reared salmonids and is difficult to detect and differentially diagnose.

The new assay is a quantitative polymerase chain reaction (QPCR) that is sensitive and specific to BCWD and is based on a single-copy gene target common to F. psychrophilum strains. This assay will help pathologists confirm the bacteria rapidly and inform inspected hatcheries of the pathogens presence.

The disease typically occurs at low temperatures and infected fish may exhibit a range of clinical signs, including large open lesions on the tail area, fraying and erosion of fins, poor appetite, and dark coloration. Bacterial coldwater disease can be transferred from fish to fish and therefore preventative measures and good culture practices are important. There is currently no vaccine for BCWD therefore hatcheries can try to reduce stress and minimize damage to the skin since these two factors tend to increase disease transmission. Removal of mortalities and sick or dying fish from ponds is also extremely important, helping to reduce the bacterial load shedding into the water.

The CA-NV Fish Health Center is looking forward to using this tool for disease surveillance and trying to minimize mortality of hatchery salmonids due to this pathogen.

Anne Bolick is a fish biologst at the California-Nevada Fish Health Center.

Contact Info: Anne Bolick, 530-365-4271 ext 213, anne_bolick@fws.gov
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