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...

Strawberry Disease in Rainbow trout – Gross Pathology

Rainbow trout with SD, showing characteristic bright-red lesions on the skin, and scale loss.

Strawberry Disease (SD) is a chronic, nonlethal skin condition that affects Rainbow Trout (Oncorhynchus mykiss) in the United States, several European countries (Scotland, England, Switzerland, Germany, France, among others), Chile and Peru (Sandoval 2017, unpublished report). In Europe it is also known as Red Mark Syndrome (RMS) or Cold-Water Strawberry Disease. The severity of the skin lesions suggests a hypersensitivity response, but hypersensitivity to what?  Affected fish respond well to immune suppressors including corticosteroids, but also to a wide range of antibiotic treatments, suggesting that...