Columnaris disease is a chronic to acute infection that affects salmonids and many species of warmwater fishes. The first description of the disease was given by Davis (1922) who named the disease and bacterium from the columnar arrangement of cells as seen in wet mounts. The bacterium causing columnaris disease was first isolated by Ordal and Rucker (1944). They identified the organism as belonging to the group known as slime bacteria or myxobacteria; because it produced fruiting bodies and microcysts, they named it Chondrococcus columnaris. Garnjobst (1945), who was unable to find fruiting bodies, renamed it Cytophaga columnaris. However, in the recently revised Bergey\u27s Manual of Determinative Bacteriology (Buchanan and Gibbons 1974) the columnaris organism and other fish pathogenic myxobacteria have been reclassified as flexibacteria. The forms of flexibacteria pathogenic to fish were recently reviewed by Bullock et al. (1971), McCarthy (1975), and Pacha and Ordal (1970)
