A contribution to the etiology of ulcer disease of trout

During the fall of 1947 and the late summer of 1948, outbreaks of ulcer disease occurred among brook trout fingerlings at the Leetown station and other hatcheries. From the ulcers, blood, and kidneys of the diseased trout were isolated bacteria which could be successfully cultivated only on media to which blood or fish‐tissue extract had been added. Some characteristics of these bacteria are described.

In a series of inoculation experiments, brook, brown, and rainbow trout were infected with pure cultures of the isolated bacteria. When the trout used for these tests were free from a latent infection of B. salmonicida, ulcer disease could be reproduced and the bacteria reisolated in pure culture from the inoculated fish. On the basis of the information on hand, it is believed that the isolated bacteria belong to the genus Hemophilus.