Flavobacterium is a genus of Gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

, non-motile and motile, rod-shaped bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 that consists of ten recognized species, as well as three newly proposed species (F. gondwanense, F. salegens, and F. scophthalmum). Flavobacteria are found in soil and fresh water in a variety of environments. Several species are known to cause disease in freshwater fish.

Flavobacterium psychrophilum causes the Bacterial Cold Water Disease

Bacterial cold water disease

Flavobacterium psychrophilum is a member of the Flavobacteriaceae family. It is a gram-negative rod-shaped bacterial pathogen that can cause bacterial cold water disease in salmonid fish. The disease typically occurs at temperatures below 13⁰C, and disease can be seen in any area with water...

 (BCWD) on salmonids

Salmonidae

Salmonidae is a family of ray-finned fish, the only living family currently placed in the order Salmoniformes. It includes salmon, trout, chars, freshwater whitefishes and graylings...

 and the Rainbow Trout Fry Disease (RTFS) on rainbow trout

Rainbow trout

The rainbow trout is a species of salmonid native to tributaries of the Pacific Ocean in Asia and North America. The steelhead is a sea run rainbow trout usually returning to freshwater to spawn after 2 to 3 years at sea. In other words, rainbow trout and steelhead trout are the same species....

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Flavobacterium columnare

Flavobacterium columnare

Flavobacterium columnare is a thin Gram-negative rod bacterium of the genus Flavobacterium. The name derives from the way in which the organism grows in rhizoid columnar formations....

causes the cotton-wool disease on freshwater fishes.
Flavobacterium branchiophilum causes the Bacterial Gill Disease (BGD) on trout

Trout

Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...

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