PASTEURELLA-PISCICIDA INFECTION IN HATCHERY-REARED JUVENILE STRIPED JACK

A mass mortality due to an infectious disease occurred in juvenile striped jack (Pseudocaranx dentex) reared at a station of the Japan Sea-Farming Association in Nagasaki Prefecture in February, 1991 and a total of about 10,000 juveniles (34 %) were lost for about one month. Administrations of oxytetracycline and oxolinic acid with food were effective to decrease the mortality. One species of bacteria was purely or dominantly isolated from diseased juveniles and identified as Pasteurella piscicida based on its morphological, biochemical, genetical (G + C contents: 40.7-41.0 mol %), and serological characteristics. An experimental infection revealed that a selected isolate was pathogenic to juvenile striped jack and yound red sea bream, the LD50 by intraperitoneal injection for the two fish species being about 10(3) and 10(7) CFU/fish, respectively. It was also demonstrated that the extracellular products (ECP) of the isolate were lethal to both fishes when it was injected intraperitoneally.