NODULAR GILL DISEASE - A UNIQUE FORM OF PROLIFERATIVE GILL DISEASE IN RAINBOW-TROUT, SALMO-GAIRDNERI RICHARDSON

An outbreak of proliferative gill disease occurred in a group of rainbow trout fingerlings kept for experimental purposes. Lesions were multifocal among filaments and uniquely severe in the distal region of affected filaments, forming nodules; this contrasted with the more common forms of proliferative gill disease in Ontario, Canada, such as bacterial gill disease, in which lesions are diffuse along and among filaments. The cause of the condition is unknown, although cells with a very distinctive morphology were closely associated with the lesions.