An Aeromonas species implicated in ulcer-disease of the cod (Gadus morhua)

Vibrio anguillarum is the most frequently isolated bacterial species involved in ulcer disease in salt water fish. However, an Aeromonas species was very often incriminated in ulcers and septicaemia in cods (Gadus morhua) in Danish coastal areas. These Aeromonas strains were very uniform in their biochemical activities only differing in growth on Simmons citrate agar, and the mean value for the guanine + cytosine content of DNA was 59 per cent with a standard deviation of 0.4. Primary serological investigations demonstrated a possible identity to O and K antigens. The most characteristic biochemical features of these strains were a gas production from glycerol but not from glucose. They were positive in lysine decarboxylase, did not produce indole, and had a typical fermentation pattern of the glycosides. Negative results were found in H2S production, phosphatase and in the utilization of NH4+ and glucose as the only source of N and C. The evident differences from the species described and subspecies of Aeromonas elucidate the weakness of the existing systems of biotyping. A broader conception of the biochemical spectrum for the individual species of Aeromonas combined with serotyping would seem to be a better system for identification, and also for an epidemiological purpose.