Abstract
The agglutinating antibody level against Pasteurella piscicida in cultured O-year-old yellowtail Seriola quinqueradiata was monitored during epizootics of pseudotuberculosis in1993 and 1994. In both years, the antibody titer slightly increased at the early period of epizootics and subsequently remained on low level. A rise of the titers was observed at the end of the epizootic, about 3 months after the first outbreak. This delayed high levels of antibody titer seem to be associated with the recent trend of prolonged epizootics of pseudotuberculosis.
