The order Cytophogales (Myxobacterales, slime bacteria, fish slime bacteria) includes an important group of opportunistic pathogens of fish that are common inhabitants of soil and water.
The gram-negative, rod or filamentous bacteria have a distinctive gliding motion and form palisading masses on infected tissue. Skin or gill lesions have slimy or cotton-like surface exudates, which usually cover surface necrosis, ulcerations, and marginal hemorrhages.
Flavobacterium columnaris, the member of this group responsible for columnaris disease (cottonmouth disease, saddleback), is most common in warm water and warmwater species of fish. Cytophaga psychrophila causes coldwater (peduncle) disease and fin and tail rot. It most commonly infects coldwater fish but can be found in warmwater fish subjected to low temperatures.
Epizootics of columnaris disease frequently occur in natural populations and high losses of fish may be observed. Wood (1974) describes strains of high and low virulence; highly virulent forms attack gill tissue and the latter strains are primarily responsible for cutaneous infections.
The lesions are especially common on the dorsal, posterior surface of the fish under the dorsal fin but may be found on any part of the body, including the mouth. In many species of fish, the first sign of the disease may be the appearance of discolored gray, patchy areas in the area of the dorsal fin. These characteristic “saddleback” lesions may progress until skin erosion exposes underlying muscle tissue. These lesions may become yellow and cratered and are often prominent in the mouth and head regions. Virulent strains of F. columnaris may attack gill tissue and cause a “gill rot” condition.
Systemic infections due to less virulent strains may occur with no apparent external signs. However, cutaneous infections seem to be more prevalent in most species of fish. Advanced cases show necrosis and ulceration of the peduncle.
A presumptive diagnosis can be made from visualization of typical myxobacteria on wet mounts of infected skin or gill tissue. If the disease is diagnosed early in the course of infection, a treatment with potassium permanganate may be efficacious. If the disease becomes chronic, it may have become systemic, in which case treatment with oxytetracycline for 10 days is recommended. Columnaris disease can be confirmed by isolation of the organism on Ordal’s or other cytophage media. Sensitivity tests are difficult to perform because F columnaria will not grow on Müller-Hinton media.
Columnaris disease can be prevented by reducing organic loading and avoiding traumatic injuries. Both Flavobacterium and Cytophaga infections can be controlled by oxytetracycline.
If the fish must be handled or crowded, certain prophylactic treatments may be administered. These include copper sulfate (CuSO4) baths for 20 min at 33 ppm or potassium permanganate (KMnO4) at 2 ppm for indefinite periods. Copper sulfate should be used with care since it is highly toxic to fish in soft water. Similarly, KMnO4 should be used with caution since it may also be toxic to certain species, particularly in soft waters with low levels of organic matter.
- Merck Veterinary Manual
- Wood, J. W. (1974) Diseases of Pacific salmon: their prevention and treatment. Wash State Dep Fish Olympia, WA pp:82
- Warren, J. W. (1981) Diseases of hatchery fish. A fish disease manual. U.S. Fish Wildl. Serv., Reg. 3, Twin Cities, MN. pp:91
- Snieszko, S.E, & G.L. Bullock. (1976) Columnaris disease of fishes. U.S. Fish Wildl. Serv., Fish Dis. Leafl. No. 45, Washington, DC. p:10