Pasteurella piscicida infection in cultured juvenile Japanese flounder

Since 1991, mortalities have occurred in 0-year-old Japanese flounder Paralichthys olivaceus (2-22 g body weight) cultured in Oita and Ehime prefectures from September to December when the water temperature ranged from 17 to 24 degrees C. The diseased fish showed dark coloration and swam inactively, but no definite symptom of the disease was observed. Daily and the cumulative mortalities were 0.01-0.6% and 0.6-4.8%, respectively. A bacterium was purely isolated from the kidney of diseased fish and identified as Pasteurella piscicida by the biological, biochemical and serological characteristics. The isolates of the bacterium were highly sensitive to most of antibacterial agents tested (oxytetracycline, ampicillin, oxolinic acid, flumequine, florfenicol, bicozamycin and fosfomycin). Oral administration of oxytetracycline hydrochloride was effective to control the epizootics. The experimental infection by intraperitoneal injection at about 18 degrees C revealed that the bacterium was pathogenic for juvenile Japanese flounder.