Flavobacterium psychrophilum

ALSO KNOWN AS: BCWD, Flexibacter psychrophilus, Cytophaga psychrophila, Rainbow Trout Fry Syndrome (RTFS), Bacterial Fry Anemia, Low Temperature Disease, Peduncle Disease, Saddleback, Tail-Rot, Systemic Myxobacteriosis

Flavobacterium psychrophilum is a Gram-negative, cold-loving bacterium responsible for bacterial cold water disease (BCWD). The infection typically begins at the extremities, causing caudal fin erosion and tissue necrosis at the peduncle, which can expose the vertebrae. Skin lesions may develop in advanced cases. Fish of all life stages are susceptible, with transmission occurring both horizontally through water and vertically from infected adults to eggs. The bacterium appears as long, filamentous rods and forms yellow, spreading colonies with thin margins on TYES agar. It does not pose a risk to humans or mammals.

Distribution: North America, Europe, Scandinavia, Japan, Southeast Asia, Australia, and Chile.

Hosts: Primarily salmonids, though other aquatic vertebrates may be affected.

Detection Methods: PCR – unspecified.

Target Tissue: Skin, fins, and systemic infection.