Macroscopic and microscopic features of ulcerative stomatitis in farmed Atlantic salmon Salmo salar

Ulcerative stomatitis is an economically unportant disease of salmon srnolts In net-pen farms of Puget Sound, Washington, USA.Gross lesions and losses from this disease typically occur 3 to 8 wk following introduction to sea water and may result in a cumulative mortality of up to 30 O/u in some pens.The disease occurs seasonally and has been present on one farm since it began production in 1987 Ulcerated lesions are limited to the oral cavity, vary in size, and are associated with areas of dentition.Mats of Cytophaga-like filamentous bacteria are associated w ~t h areas of ulceration and necrosis and often extend into the underlying bone Scanning electron mlcroscopy demonstrated mats of filarnentous bacteria overlying ulcerated areas and biofilms of f~lamentous bacter~a adhering to tooth surfaces at the ginglval-enameloid interface and invading the gingival epithelium.Our findings suggest the filamentous bacterium plays a major role in the pathogenesis of ulcerative stomatitis in salmon smolts.