Nodular gill disease (amoebic gill infestation) in arctic char, Salvelinus alpinus

Two groups of Arctic char (Salvelinus alpinus) and one of rainbow trout (Oncorhynchus mykiss) from a commercial fish farm in eastern Canada were found to have mixed infection of the gills with Flavobacterium branchiophilum (the causative agent of bacterial gill disease (BGD) and amoebae similar to those responsible for nodular gill disease (NGD). The diagnoses were confirmed by immunofluorescence antibody testing and transmission electron microscopy. The gill lesions were typical for a mixed BGD and NGD infection and the extensive and dramatic hyperplasia of filament epithelium was characteristic of NGD. The diagnosis of NGD in Arctic char in eastern Canada represents both a geographical and species extension for this infection. To date, within commercially farmed salmonid populations, NGD has been reported only in central Canada in rainbow trout.