ferment glucose or mannite and was nonpathogenic to frogs. Though it 

 resembled B. salmonicida in chromogenesis, it was clearly differentiated 

 by its lack of fermentative properties, nonpathogenicity, and ty 

 serological tests. 



COMPARISON WITH ULCER DISEASE 



Ulcer disease was the first disease of trout to be studied in the 



United States. Short:iy after its discoveiy, furunculosis appeared and 



because of the marked superficial resemblance betTreen the two diseases, 

 much confusion has resulted (Fish 1935). 



Ulcer disease was first described by Calkins (1899) who found it 

 present in epidemic form at a hatchery on Long Island, New York. Calkins 

 believed that this disease v/as caused by a protozoon, but it is now 

 generally recognized that there is little evidence to support this 

 conclusion. Ulcer disease has since been described by many authors 

 (Marsh 190A, Fish 193/i, 1935, Wolf 1938, 19A0, Davis 1946, Snieszko and 

 Friddle 19'49b). 



Fish (1934) found that the only organism pathogenic to trout which 

 could be isolated from an outbreak of ulcer disease at a trout hatchery 

 in Nevf York State was Pseudomonas hydrophila . This organism is also 

 the etiological agent in "red-leg" of frogs (Sanarelli 1891, Russel 1898, 

 Emerson and Norris 1905, Kulp and Lackman 1934). Reed and Toner (1941) 

 have also reported it in pike vdth "red-sore" in eastern Ontario. This 

 organism differs from B. salmonicida in fermentative properties and in 

 the lack of pigment production. 



In 1946, Davis stated that a worker in his laboratory isolated a 

 bacterium from fish with ulcer disease, which, on inoculation, produced 

 lesions indistinguishable from typical ulcers of natural infection. This 

 organism had, however, the same cultural characters as Bacteriiim 

 salm.onicida . Brook trout inoculated vri.th this organism by a slight 

 prick mth a needle developed a typical epithelial tuft at the site of 

 inoculation (see below). Similar inoculations with standard B. 

 salmonicida cultures failed to produce such a lesion. 



On passage through several fish the organism recorded by Davis 

 (1946) increased in virulence and on inoculation into healthy trout 

 produced lesions indistinguishable from those found in typical 

 furunculosis. When first isolated, only superficial lesions were 

 produced by inoculation, and on autopsy, liver, kidney, and spleen 

 appeared normal which is characteristic of ulcer disease (see above). 

 Later inoculations produced deeper lesions more like those of furunculosis 

 and bacteria were found in the Icidney, liver, and spleen. There is, 

 therefore, much evidence to support the view that ulcer disease may be 

 caused by a less virulent strain of E. salmonicida. 



52 



