Identification of pathogenic bacteria associated with the occurrence of ‘red spot’ in sea mullet, Mugil cephalus L., in south‐eastern Queensland

An investigation was undertaken to determine the bacterial species associated with the fish disease known as ‘red spot’ which affected wild fish stocks in south‐eastern Queensland. Outbreaks of the disease in the Noosa River were examined with particular reference to the sea mullet, Mugil cephalus. The bacterial flora of the skin of healthy fish as well as those exhibiting early and advanced lesions was determined. In the lower Noosa River estuary, Vibrio anguillarum was the sole organism associated with very early lesions. It was later shown that V. alginolyticus was also associated with V. anguillarum in early lesions, but was considered to be a secondary invader. Aeromonas hydrophila was isolated from advanced lesions on fish taken in freshwater reaches of the river. This organism was also regarded as a secondary invader.