MEGALOCYTIVIRUS INFECTIONS IN FISH: AN OVERVIEW, SELECT CLINICAL CASES, AND MANAGEMENT R. Yanong, VMD1* and T. Waltzek, DVM, PhD2 1Tropical Aquaculture Laboratory, Fisheries and Aquatic Sciences Program, SFRC, IFAS/University of Florida, 1408 24th St. SE, Ruskin, FL 33570 USA; 2Infectious Diseases and Pathology, College of Veterinary Medicine, University of Florida, Bldg #1379, Mowry Road, Gainesville, FL 32610 USA ABSTRACT Megalocytiviruses, an emerging group of icosahedral, double-stranded DNA viruses, can cause systemic disease and high morbidity and mortality in numerous fish species. Nearly all clinical isolates, likely strains of the same virus species, have been divided into three major subgroups: a) infectious spleen and kidney necrosis virus (ISKNV); b) red sea bream iridovirus (RSIV); and c) turbot reddish body iridovirus (TRBIV). Research suggests that megalocytiviruses may have lower host-specificity than other viruses. Susceptible aquarium fish include cichlids, livebearers, and gouramies. Susceptible food and game fish species include carangids, scombrids, serranids, cobia (Rachycentron canadum), largemouth bass (Micropterus salmoides), barramundi (Lates calcarifer), redfish (Sciaenops ocellatus), and hybrid striped bass (Morone saxatilis × M. chrysops). The first megalocytivirus discovered in a wild North American fish was described from the threespine stickleback (Gasterosteus aculeatus). Clinical signs include lethargy, anorexia, darkening, abnormal swimming or positioning, increased respiration, ascites, ulceration, hemorrhages, anemia, fin erosions, white feces, and increasing mortalities. Megalocytoviruses target the spleen and kidney, but other tissues (liver, muscle, gonad, heart, gill, gastrointestinal tract) may be affected. Histopathologically, large, basophilic or pale, foamy cells are present in affected tissues. Virus isolation, EM, serology, and PCR help confirm the diagnosis. Anecdotally, warmer temperatures appear to facilitate disease. Megalocytiviruses can be spread by cohabitation or exposure to virus-contaminated water. Consumption of infected tissues and use of virus- contaminated equipment are also risks. Good husbandry, management, treatment of concurrent infections, and biosecurity help reduce introduction and spread. Commercial vaccines are now available internationally, but not in the United States. 2014 Proceedings Association of Reptilian and Amphibian Veterinarians 39 .