Epizootic ulcerative syndrome (red spot disease)

  • A silver perch with an ulcer
    A silver perch with an ulcer



Epizootic ulcerative syndrome (EUS) or red spot disease


EUS or red spot disease is an ulcerative disease of fish caused by the fungus Aphanomyces invadans. It often occurs in estuarine fish anywhere along the east coast and in the Gulf of Carpentaria.


In Queensland, factors that initiate EUS outbreaks are not always consistent but usually follow the first heavy rainfall in spring or following the first rains of the wet season in northern Queensland. Research has found good evidence to suggest these EUS outbreaks are associated with acid water. This is water run-off from disturbed acid sulphate soils or leaf litter (tannic acids) after periods of little rain.

Where the disease occurs

EUS affects a wide range of native fish species in Queensland, such as mullet, bream, whiting, pikey bream, eels and catfish. The disease can also be seen in farmed freshwater fishes and inland freshwater rivers.

The disease also occurs in New South Wales, Victoria, the Northern Territory, and Western Australia, as well as many Asian countries.

The disease in animals

Initially, the gross signs of early disease are characterised by small, multiple red spots over the skin. These spots are hard to see, and the first signs people typically observe are the deep skin ulcerations that occur as the disease progresses. These ulcers can be on any part of the body or head and range from red to a dirty-brown colour. The ulcers can extend down to the bone or into the abdominal cavity. Badly affected fish can survive for some time but are unmarketable.

Not all cases of EUS are lethal, and some fish can heal leaving noticeable scarring; however, many affected fish die as a result of a failure of osmoregulation or secondary bacterial infections - the consequence of the severe skin and muscle damage.

Symptoms of EUS
  • multiple small red spots over the skin
  • deep-red to brown skin ulcers
  • weak swimming or swimming near the surface.
EUS and people

EUS is not known to cause disease in humans. However, it is recommended that people should not eat EUS-affected fish as water bacteria may leak into the flesh and contaminate the flesh.

Last updated 14 January 2014