EDWARDSIELLOSIS IN WILD STRIPED BASS FROM THE CHESAPEAKE BAY

The first epizootic of edwardsiellosis, caused by Edwardsiella tarda, is described. The epizootic occurred in the Chesapeake Bay, Maryland ( USA) during the summer and autumn of 1994, and affected wild adult str iped bass (Morone saxatilis). Clinical signs included numerous irregul ar coalescing hemorrhagic ulcers on the body and fins that were distin ctly malodorous. Internally, the body cavity was filled with abundant yellowish or sanguinous mucoid fluid, and the visceral organs had mult iple tiny white foci. The intestines contained thick white opaque mucu s. Histopathological lesions included ulcerative dermatitis, cardiac e ndothelial hyperplasia, and necrotic foci and granulomata in multiple organs. A bacterium isolated in pure culture was characterized taxonom ically and serologically as the wild-type or classical biotype of E. t arda. In infectivity trials, it was pathogenic for striped bass, gilth ead seabream (Sparus aurata), and turbot (Scophthalmus maximus) with a n LD50 of about 10(5) cells; however, the isolate was non-virulent for mice (LD50 > 10(8) cells). The isolate also was resistant to the bact eriolytic activity of normal fish skin mucus.