Flavobacterium psychrophilum in salmonids – Gross Pathology

Figure 2. F. psychrophilum infection in rainbow trout. Note the classical “peduncle disease” with necrosis and darkening of tissues distal to the anal fin.

Flavobacterium psychrophilum is a ubiquitous Gram-negative filamentous and yellow-pigmented bacterium, and as the name suggests, it thrives in cooler water temperatures, causing disease in freshwater fish at 4-12°C. It likes connective tissues, especially those in younger fish in which it causes diseases such as bacterial cold-water disease (BCWD or peduncle disease) and rainbow trout fry syndrome (RTFS). As fish get older and the proportions/chemistry/locations of connective tissue change, the types of lesions also change. F. psychrophilum is responsible for significant economic losses in salmonid aquaculture...

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