Abstract

The first reported epizootic of fish pasteurellosis caused by the bacterium Pasteurella piscicida in a cultured population of fish in the U.S. is described. The epizootic occurred in populations of striped bass (Morone saxatilis) cultured in earthen, brackish-water ponds at the Claude Peteet Mariculture Center, Gulf Shores, AL. Losses of up to 49,000 fingerlings (80% of existing stock) occurred over a 3-wk. period. Oxytetracycline was administered via the feed within 48 h of the onset of mortality. Oxytetracycline residues in tissues of fish sampled during the treatment period were quantitated by a fluorometric method. The isolated bacterium was characterized biochemically and serologically. The sensitivity of the bacterium to various antibiotics was determined, and the minimum inhibitory concentration of oxytetracycline was determined to be 0.25 ppm. Salient histopathological features of the disease in striped bass are described.