Aetiology of an ulcerative disease in goldfish Carassius auratus (L.): microbiological examination of diseased fish from seven locations

A comparative diagnostic study was conducted on goldfish, Carassius auratus (L.), with a cutaneous ulcerative disease from five locations in the United States and one each in England and Japan. Fish were examined for parasites, viruses and bacteria. Fish from all locations examine d were infested by ectoparasites; no single parasite species was common to all locations. No virus‐associated cytopathology was observed in fathead minnow (FHM) or adult goldfish (CAR) monolayer cell cultures inoculated with homogenates of cutaneous lesions, kidneys and livers from diseased fish. The only bacterium cultured from fish from all locations was an atypical, often late‐pigmenting strain of Aeromonas salmonicida. This organism was isolated from 64 of 83 (77%) of the total lesions cultured and was most prevalent in early lesions. A second commonly isolated organism was Aeromonas hydrophila, which was cultured from fish at four of the seven locations and from 28 (34%) of the total lesions cultured. A. hydrophila was most prevalent in terminal lesions. From these studies it was concluded that A. salmonicida was the probable cause of ulcers noted In the cases examined an d that A. hydrophila was a secondary invader.