Improving fish production in freshwater aquaculture and in estuaries by reducing losses due to Epizootic Ulcerative Syndrome (EUS)

• Agency for Agricultural Research and Development, Indonesia
• Department of Agriculture, Philippines

Declining fish stocks and losses caused by diseases are a major constraint to improving the nutrition and income of rural people. EUS, a disease characterised by ulceration and mortalities in wild and cultured freshwater fish affects more than 30 species of commercially important freshwater and estuarine cultured and wild fish.

Rational control and prevention methods remain a problem, as the pathogenesis of EUS is not understood. Patterns of occurrence in the Asia-Pacific suggest an infectious cause linked with the fungus Aphanomyces sp., which invades the skin of fishes exposed to rapid water changes such as decreases in alkalinity, hardness, chloride concentrations and fluctuations in pH.

In Australia and the Philippines, EUS is most often seen in estuaries with acid sulfate soils in their lower catchments, and in Indonesia a link between the occurrence of EUS in rivers and the presence of peat (acid) soils in their catchments has been observed.

This project stemmed from discussions between Australian and Filipino epizootic ulcerative syndrome (EUS) researchers and an independent Indonesian funding request. Led by Australian scientists from NSW Fisheries experienced in EUS research, they will work with scientists in Indonesia and the Philippines with similar experience.

The project has two main objectives:

to develop control and prevention measures for EUS in important Asian freshwater aquaculture systems (ponds in Indonesia and rice-fish systems in the Philippines); and

to identify the major disease determinants for EUS in estuarine fish, with emphasis on the role of run-off water derived from acid sulfate soil areas.

The collaborators will look at interactions between EUS prevalence in selected fish populations, Aphanomyces sp. propagule concentrations in water, and selected water quality attributes. Having identified major factors in the pathogenesis of EUS, they will develop in years 2 and 3, control and prevention measures based on elimination of, or reduction in the magnitude of one or more of these disease determinants.

In Australia, researchers at the Regional Veterinary Laboratory, Wollongbar, will reproduce EUS and attempt to validate suspected major disease determinants arising from the field studies in Indonesia and the Philippines. Pathologist experts in aquatic mycology from Oonoonba Veterinary Laboratory, Townsville will carry out complementary laboratory-based fungal studies.

Additional funding to the project will enable a 7 month study in Karnataka, India, involving seasonal EUS outbreaks in farmed estuarine fish, including Mugil and Sillago species, held in ponds fed by estuarine water. This work will provide an opportunity to study environmental and mycological aspects of the outbreaks in confined fish populations.