Photobacterium damselae subsp piscicida outbreak in cage-reared Atlantic bluefin tuna Thunnus thynnus

High mortalities of the bluefin tuna Thunnus thynnus reared in Adriatic Sea cages Occurred during spring 2004. Outbreaks had been previously reported at the same facility in similar conditions in the tuna population harvested in winter 2003. Fish displayed no external clinical signs of disease except for changed coloration and atypical swimming. and gross pathology was limited to general signs of septicemia. Histological and bacteriological findings suggested an epizootic outbreak of pasteurellosis. The pathology Suggested in acute infection with the changes characteristic of septicemia. Most Fish died in 1-2 d without gross pathology, possibly because of the virulence of the bacterial strain or reduced resistance of the fish. A low percentage of fish developed a chronic form of infection with disseminated granulomas in kidneys but also showed no gross pathology. Tuna parasitofauna Was evaluated and did not appear to affect the development and the course of the disease.