Diagnosis of vibriosis in a commercial oyster hatchery epizootic: Diagnostic tools and management features

Abstract Epizootic vibriosis of larval American oysters, Crassostrea virginica , in a commercial hatchery was studied by examining hatchery production records and also examining larval oysters with interference microscopy, the dye exclusion test, histological techniques and vibrio-specific fluorescent antibody methods. Two larval spawns sampled for laboratory analysis showed 95% or greater mortality in 6 of the 7 groups sampled. Hatchery production was severely depressed over a 5-week period. The production for 1979, the year in which the disease occurred, was only one-third of that of the previous year. Both examination of live larvae and histological analysis demonstrated that pathological lipid deposition in the digestive gland and other digestive system organs was a consistent sign of the disease. The trypan-blue dye exclusion test was a rapid and simple method which facilitated recognition of some of the early pathological changes in larval oyster vibriosis. The antibody test provided a rapid and specific diagnosis of the etiologic agent as a Vibrio spp. The clinical, histological and immunofluorescent findings in this case of larval oyster vibriosis in a commercial hatchery demonstrated a pathogenesis which was identical to that previously reported in experimental vibriosis.