The therapeutic effects of ampicillin, applied orally, on the pseudotuberculosis of yellowtails, Seriola quinqueradiata and Seriola purpurascens, were studied.
1. Yellowtails artificially infected with P. piscicida were given ampicillin by oral route at the doses of 0.1, 1, 10 and 100 mg/kg·b.w. The mortality rate of each dose was 70, 40, 30 and 0%, respectively.
2. Ampicillin was also effective at the dose of 12 mg/kg·b.w. in reducing the mortality rate of yellowtails naturally infected with P. piscicida.