Flexibacter columnaris syn. Cytophaga columnaris, the causative agent of columnaris disease, affects many species of freshwater fish and can cause extensive skin and gill damage and ultimately death. The bacteria are long and slender, with gliding motility achieved by flexing movements. They grow well on low nutrient media producing pale yellow rhizoid colonies. Cellulose starch and agar are not hydrolysed but casein and gelatin are broken down. They have been classified by serotyping and on the basis of sensitivity to the lytic colicin-like substances which they produce. The mol % G+C of the DNA has been reported to be from 30 to 43%.
Flexibacter maritimus causes salt water columnaris. It is similar to F. columnaris but has an obligate requirement for seawater. Gliding bacteria, other than this and F. psychrophilus, have been associated with disease in freshwater and marine fishes but further work is needed to clarify their taxonomy and pathogenicity (Wakabayashi & Egusa 1974, Schneider & Nicholson 1980).