A NEW BACTERIUM (HEMOPHILUS PISCIUM N. SP.) FROM ULCER DISEASE OF TROUT

Outbreaks of ulcer disease among hatchery brook trout (Salvelinus fontinalis) have been described by Fish (1934) and Wolf (1938, 1940). Fish frequently isolated Psudomonas hydrophila from the infected trout. This common water bacterium was also isolated from ulcer disease in pike (Esox lucius) and brook trout by Reed and Toner (1942). Bacterium salmonicida, the cause of fish furunculosis, also has been isolated from trout with ulcer disease, as reported by Davis (1946). It seems likely that the upper picture in the color plate (Taf. [XXII XXXI) in Plehn's book (1924) depicts ulcer disease rather than furunculosis. In an outbreak of ulcer disease among brook trout at Kearneysville, West Virginia, Snieszko and Friddle (1950) regularly isolated a Hemophilus-like bacterium. Subsequently these authors isolated the same bacterium from outbreaks of ulcer disease in Maryland, Pennsylvania, Massachusetts, and Rhode Island. Some of the epizootics in trout were complicated by furunculosis, and in such cases B. salmonicida was also isolated. Trout artificially inoculated with this Hemophilus-like microorganism developed typical lesions and usually died. From such trout the same bacterium was then recovered. This rendered more probable an etiological relationship between this hitherto unknown bacterium and the ulcer disease of trout. Diagnosis of ulcer disease is often complicated by the occurrence in the trout of other easily isolated bacteria such as B. salmonicida, P. hydrophila, and water saprophytes. Therefore methods are here described for the isolation, cultivation, and identification of the Hemophilus-like bacterium believed to be the etiological agent of ulcer disease. Some studies on growth factor requirements are also described.