Evaluation of the efficacy of an ultrafine preparation of oxolinic acid in the treatment of pseudotuberculosis in yellowtail.

Abstract

Antibacterial activity of oxolinic acid (OA) against Pasteurella piscicida isolated from yellow-tail was studied, and field trials were cazried out in order to compare the efficacy of ultrafine (1.0μm in diameter) and ordinary (6.4μm in diameter) preparations of OA against pseudotuberculosis in yellowtail. The MIC90 values of OA, oxytetracycline, thiamphenicol and ampicillin against P. piscicida were 2.66, 35.70, >100 and 32.98μg/ml, respectively. In the field studies, each of the above two preparations of OA was mixed into minced sand eel and administered in doses of 10, 20 and 30 mg/kg of the ultrafine preparation and in a dose of 30mg/kg of the ordinary preparation for s days after the onset of pseudotuberculosis outbreak. Both prepazations reduced the mortality of the fish, and in group mortality, the ordinary preparation of OA at the dose of 30mg/kg was intermediate between 10 and 20mg/kg of the ultrafine pre-paration, whcn the mortality during and after the medicadon period and the mortality after the medication were both compared among the groups by statistical analysis.