Clinical, microbiological and epidemiological findings in recent outbreaks of goldfish ulcer disease due to atypical Aeromonas salmonicida in south‐eastern Australia

The spread of goldfish ulcer disease (GUD) from Victoria to New South Wales, Australia, and the first isolation of Aeromonas salmonicida from wild goldfish are reported. Cultural, biochemical and protein SDS‐PAGE characteristics of these recent isolates are compared with those of existing Australian isolates, with strains recovered from goldfish in Italy and the USA (atypical strains) and with strain ATCC 14174 (typical strain). The Australian isolates were identical and closely resembled the exotic atypical strains. Although there were several biochemical differences between the atypical isolates and the typical ATCC 14174 strain, the results of SDS‐PAGE confirmed that these strains were closely related. The homology of the Australian and overseas strains recovered from goldfish supports the common view that A. salmonicida was introduced first into Australia with diseased goldfish in 1974. The three widely separated outbreaks of GUD reported here confirm that an atypical strain of A. salmonicida is now endemic in Australia.