Disseminated hexamitosis in sea-caged Atlantic salmon Salmo salar

A flagellated parasitic protozoan, similar to Hexamita salmonis, was found in large numbers in all internal organs, except muscle, in diseased sea-caged postsmolt Atlantic salmon (200 to 250 g). In postsmolts, whitish granulomatous nodules, containing large numbers of Hexamita sp., were present in kidney and liver. In large salmon (4 to 5 kg), the most severe lesions were boils in caudal muscle. These unusual cases of hexamitosis were recorded at 4 fish farms in northern Norway (approximately 70" N). No bacteria or virus that could be linked to the disease were demonstrated.