Abstract

Light-microscopic examinations revealed a consistent correlation between a syndrome of mass mortality in hatchery-raised larval and juvenile barramundi (Lates calcarifer) and vacuolation in the brains and retinas of these fish. Large amounts of picorna-like viral particles were found associated with these lesions when brain and retinal tissue was examined by electron microscopy. Epizootological data suggested that vertical transmission of the infectious agent is not a common occurrence, and most transfer of infection is probably from previously-hatched juveniles to recently-hatched larvae. These data include the observation that adequate isolation of older juvenile fish from recently-hatched larvae, coupled with between-hatch cleaning and disinfection of the premises, has apparently controlled mass mortalities in one large hatchery.