First Report of Fish Pasteurellosis from Malta

The first documented outbreak of fish pasteurellosis in an offshore cage farm for gilthead seabream Sparus auratus in Malta is described. The pathogen entered the farm with juvenile fish and the disease occurred within 2 months of their arrival. Losses first affected small fish (10 g) and then affected larger fish (280 and 325 g). Mortalities were low (L5% in small fish and 0.2% in the larger fish) and the disease was treated successfully with flumequine. The pathogen isolated from the outbreak was cultured and appeared to be biochemically and phenotypically similar to other strains of Pasteurella piscicida (now known as Photobacterium damsela subsp. piscicida, Ph.d.p.). Western blot analysis of this isolate and other Ph.d.p. isolates with anti-Ph.d.p. rabbit polyclonal and mouse monoclonal antibodies revealed similar reaction patterns and, therefore, antigenicity. The pathological and immunohistochemical appearance of the disease was typical of fish pasteurellosis.