An iridovirus from 2 species of freshwater tropical imported fish was examined for its antigenic and biochemical properties and virulence for 3 species of food fish. The virus was found in both guppy (Poecilia reticulata) and doctor fish (Labroides dimidatus). The virus replicated in numerous fish cell lines including BF-2, CCO and EPC. Virus titers reached 10(8) TCID50/ml in each cell line. The virions had similar size and morphology to those previously reported to cause systemic infections among catfish in Europe and from redfin perch and rainbow trout in Australia. A comparison of the ornamental fish iridovirus with these systemic agents indicated that all share common antigens detected by indirect fluorescent antibody tests and Western blots. Additionally, polymerase chain reactions using primer sets developed for the red fin perch virus, amplified a segment of genomic DNA from the ornamental fish isolate. An examination of the virulence of the ornamental fish isolate for 2 important food fish species, rainbow trout (Oncorhynchus mykiss) and channel catfish (Ictalurus punctatus), indicated the former species was susceptible although mortality was low. Dead fish had significant lesions in the liver and kidney and had titers of virus greater than 10(8) TCID50/g. We speculate that these iridoviruses, first detected in Australia in redfin perch, are all related strains in the Ranavirus genus that may have reached these geographically distant sites by movements of ornamental fish.