Results of a previous FIRTA-funded project (86/53) indicated that red spot disease (RSD), a cutaneous ulcerative disease of estuarine fish, is caused by a number of interacting factors. The study showed that lower catchment rainfall is an important determinant of RSD outbreak occurrence. The study also showed that dissolved oxygen concentrations at representative estuarine sites fell to very low levels within 7-10 days of such rain events. Concentrations remained low for a further 8-10 days, as flood waters receded. These findings indicate that rapid and severe changes in one or more water quality parameters, including dissolved oxygen concentrations, pH, salinity and temperature, may be important in initiating RSD outbreaks. Another key finding of the study was that RSD ulcers are a consequence of massive invasion of skin and underlying muscle by morphologically similar, non-septate fungal hyphae. These invasive hyphae cause extensive tissue destruction and provoke a characteristic granulomatous inflammatory response.

There was no evidence that bacteria, cutaneous ectoparasites or viruses were essential in induction of lesions.

The present project was designed to identify water quality parameters important in induction of RSD lesions, and to identify invasive fungi associated with ulcers.