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THE ULCER DISEASE (BLACK OPHTHALMIA?) OF 

 RAINBOW TROUT. 



{Micrococcus jjyoyenes.) 



By R. Grbig Smith, M.Sc, Macleay Bacteriologist to the 



Society. 



During the months of February and March of this year a 

 disease appeared among the rainbow trout, Sahyio irideus, in the 

 fish hatcheiy of the New South Wales Government at Prospect. 

 The hatchery adjoins the reservoir of the Sydney water supply, 

 and under normal conditions is furnished with a continuous supply 

 of pure water. Owing, however, to the drought the water in the 

 reservoir fell very low, and the tanks in the hatchery did not 

 receive an adequate supply. As a result the water in the tanks, 

 which were carrying a maximum number of one, two and three- 

 year old trout, became foul, and there can be little doubt that 

 this was indirectly responsible for the outbreak of the disease. 

 When the supply again became regular the disease almost 

 disappeared. 



The disease is characterised by the fishes having a sluggish, 

 aimless movement in the water, in which they generally, keep 

 near the surface. The snout and tail become whitish from their 

 rubbing the snout against the sides of the cement tank, and at 

 other times resting vertically in the water and moving the tail 

 to and fro against the cement tank bottom. When the eye 

 becomes affected the lens whitens and the eye decays, leaving an 

 empty capsule. The epidermis generally becomes dark in colour, 

 and this, in conjunction with the atrophy of the eye, has given 

 rise to the name of the disease, black ophthalmia. 



