Journal of Fish Diseases 18 1 49 57

A skin disease of intensively reared rainbow trout in Ontario, Canada, known to the farmers as 'no-mucus skin disease' , is reported for the first time. It is characterized by erosive and ulcerative lesions found mainly on the flanks of fingerlings which results in exposure of the tips of the scales. Colonies of bacteria were seen clustered around the the mucous cell pores and under running the margins of the epithelial cells. The cause of this condition is unknown, although the response of affected fish to formalin treatment and the presence of bacteria in skin scrapings suggests that bacteria are the cause.