Abstract
In Atlantic Canada, Moritella viscosa is often cultured from Atlantic salmon skin ulcers in the summer and autumn months when water temperature is > 10 °C. The objectives of our study were to: 1) describe the development of skin ulcers associated with an Atlantic Canadian M. viscosa isolate; and 2) determine if this isolate could be transmitted horizontally between fish via water under laboratory conditions. Atlantic salmon in salt water were bath-immersed with M. viscosa (5.6 × 106 cfu ml-1) at 10.9 ± 0.2 °C. After observing skin lesions, water from each bath-challenge tank was diverted to a “delayed-challenge” tank with previously unexposed fish. The initial bath-challenge fish expressed clinical signs of skin ulcers within four days of exposure. Fish that were not sacrificed during our trial fully recovered by 26 days post-challenge. No clinical signs of disease were observed in fish from the delayed-challenge tanks. Our results suggest skin lesions induced by an M. viscosa isolate from Atlantic Canada have similar pathology to winter ulcer disease described in Europe. Most bath-challenged fish were not systemically infected until the development of visible skin ulcerations. None of the delayed-challenge fish were infected with M. viscosa, which suggests horizontal transmission via the water was not sufficient to cause disease in our study.
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