A natural outbreak of columnaris disease among wild adult and hatchery-reared fingerling salmon in the State of Washington is described. The disease is identified by the recovery of the causative organism, Bacillus columnaris Davis, which may be readily identified by its characteristic action in forming columns on the surfaces of infected material held in a water mount on a microscope slide. The gross lesions vary in appearance according to the particular organ affected but are formed, essentially, by the progressive necrosis and disintegration of the tissues. The tissues primarily affected are skin, body musculature, and the gills. Cultivation of the causative organism in tryptone solutions is recorded. Controlled, laboratory-induced infections indicate that among the cold-water fishes, columnaris disease is of little consequence to fingerlings at water temperatures below 55° F., but becomes highly pathogenic at temperatures in excess of 70° F. Between these temperature thresholds, the degree and severity of the infection is markedly influenced by factors adverse to the host. No effective control measures have been found.
