シマアジ稚魚のPasteurella piscicida感染症

1991年2月に長崎県下で中間育成されていたシマアジ稚魚が大量斃死した。斃死は約1か月続き, オキシテトラサイクリンおよびオキソリン酸の径口投与により終息した(死亡率34%)。病魚には顕著な外見的症状は認められなかったが, 臓器から一種類の細菌が分離され, 生物学的・血清学的性状からPasteurella piscicida に同定された。分離菌は健康なシマアジ稚魚に強い病原性を示し, またシマアジおよびマダイに致死性を有する菌体外毒素を産生した。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 LD_50 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