302 FISH HATCHERY MANAGEMENT 



COLUMNARIS DISEASE 



The causative agent of columnaris disease historically has been named 

 Chondrococcus columnaris, or Cytophaga columnaris, but now is classified as 

 Flexibacter columnaris in Bergey's Manual of Determinative Bacteriology. The 

 agents are long, thin, gram- negative bacteria that move in a creeping or 

 flexing action, and that have a peculiar habit of stacking up to form dis- 

 tinctive columns, hence the name "columnaris." 



Columnaris most commonly involves external infections but can occur as 

 an internal systemic infection with no visible external signs. Externally, the 

 disease starts as small, grayish lesions anywhere on the body or fins; most 

 commonly the the lesions occur around the dorsal fin or on the belly. The le- 

 sions rapidly increase in size and become irregular in shape. As the lesions 

 get larger, the underlying musculature can be exposed. The margins of the 

 lesions, and occasionally the centers, may have a yellowish color due to 

 large aggregations of the bacteria. Frequently, lesions may be restricted to 

 the head or mouth. In Pacific salmon and warmwater fish, particularly cat- 

 fish, lesions may be confined to the gills. Lesions on the gills are character- 

 ized by yellowish- brown necrotic tissue beginning at the tip of the fila- 

 ments and progressing toward the base. 



Columnaris disease usually is associated with some kind of stress condi- 

 tion such as high water temperature, low oxygen concentration, crowding, 

 and handling. Under appropriate conditions, columnaris may take an ex- 

 plosive course and cause catastrophic losses in 1 or 2 days after the first ap- 

 pearance of the disease. Therefore, it is incumbent upon the fish culturist 

 to maintain the best possible environmental conditions for the fish and to 

 minimize any stress conditions. 



Although columnaris disease attacks practically all species of freshwater 

 fish, catfish are particularly susceptible. In warmwater fish, most outbreaks 

 of columnaris occur when the water temperature is above 68°F, but the 

 disease can occur at any time of the year. Columnaris disease is common in 

 salmonids held at water temperatures above 59°F. Progress of the disease 

 usually is faster at the higher temperatures. 



Flexibacteria are common inhabitants of soil and water. They commonly 

 are found on the surface of fishes, particularly on the gills. The stress of 

 crowding, handling, spawning, or holding fish at above- normal tempera- 

 tures, as well as the stress of external injury, facilitates the transmission 

 and eruption of columnaris disease. 



Presumptive diagnosis of columnaris is accomplished best by microscopic 

 examination of wet mounts of scrapings from lesions and detection of many 

 long slender bacteria (0.5 x 10 micrometers) that move by flexing or 

 creeping movements and form "haystacks" or "columns." 



Preventative measures include maintenance of optimum water tempera- 

 tures for salmonids, reduced handling during warm weather, maintenance 



