An epizootic disease in redfin perch, Perca fluviatilis, in north-east Victoria, Australia, was found to be caused by a recently described iridovirus. The acute disease is characterized by necrosis of the renal haematopoietic tissue, liver and spleen, with variable involvement of the pancreas. Transmission studies confirmed that the iridovirus is the causative agent of the disease. High mortalities occurred in 0+ juveniles in early summer and appear to be a recurrent seasonal event, whereas more sporadic outbreaks occurred in older age classes. Carrier fish were detected at low prevalence. The disease is described as epizootic haematopoietic necrosis (EHN) and is the only viral disease of fish known to occur in Australia.