The rock oyster industry in Australia is currently valued at around $28 million annually. The current output is about half of the industry peak in the late 1970’s. For the industry to survive in the long-term requires the ability to service what may become a premium domestic market demanding a high quality product. The expansion of the industry is likely to be available only from international export, which in turn requires compliance with international regulations on oyster health with a transparent health audit trail. The rock oyster is potentially positioned for re-emerging export success, being a unique product with an extended shelf-life relative to other oyster species (e.g. the Pacific oyster, Crassostrea gigas) and this is an opportunity that should be exploited by the industry.

The techniques of surveillance and diagnosis for molluscan pathogens required by the OIE for imported oyster products are not only stringent and accepted as the worldwide standard, but are also applicable to domestic requirements within Australia. In essence, the regulations state that appropriate diagnostic tests are applied for detecting the presence of pathogens of molluscs (microscopic identification techniques with the potential for specific molecular identification using monoclonal antibodies or DNA probes) which have been collected as part of a surveillance program within delimited coastal zones. The sample size, period and frequency are determined with reference to the cycle of infection of the particular pathogen and its prepatent period. There is an initial 2 year period of surveillance before a zone can be granted a disease-free status, with ongoing surveillance required for this status to be maintained.

The development of a zoning policy framework for marteiliosis will provide a valuable opportunity to implement and field-test Australia’s zoning policy guidelines in a practical context to assist with the development of further zoning policies for diseases of aquatic animals. Considerable interest has already been expressed in the case study by State authorities and it will be discussed at an Aquatic Animal Disease Zoning Workshop in Canberra on 23 January 2001, hosted by the National Offices of Animal and Plant Health. Furthermore, the development of the zoning policy will be of direct benefit to the oyster industry by facilitating domestic and international market access, and through identifying and protecting the remaining disease-free production areas

Marteiliosis (QX disease, aetiological agent the protozoan parasite marteilia sydneyi) typically causes serious, seasonally recurrent mortalities in farmed and wild rock oysters in eastern Australia. The disease is listed as notifiable by the OIE and is included on the Australian National List of Reportable Disease of Aquatic Animals.

The OIE has recently adopted the concept of zoning to facilitate trade and to prevent spread of disease within a country. In turn, Australia has recognised the value of zoning in its aquaculture industries with the adoption and endorsement of Zoning Policy Guidelines by Standing Committee on Fisheries and Aquaculture.

The establishment of scientifically defensible zoning and translocation policies, particularly in relation to QX disease control, is critical to the long term development of the rock oyster aquaculture industry. NSW Fisheries currently prohibits movement of oysters from known QX infected estuaries to those thought to be free of infection. However, given the many millions of rock oysters translocated annually between NSW estuaries of undetermined disease status, there is an urgent need to accurately identify free an infected zones. This, in turn, depends upon the availability of standardised, validated diagnostic tests.

Histopathology is currently viewed as the 'gold standard' for QX disease diagnosis, while preliminary comparative data (Callinan and Wesche, unpublished data) suggest that an alternative cytological method, stained tissue imprints of oyster digestive gland, has a sensitivity of 60% and specifically of 100%. Recently, however, there have been major advances in development of PCR tests for marteiliosis (Berthe et al. 2000; Kleeman and Adlard 2000). It is possible that PCR can be used to confirm presumptive/inconclusive diagnoses obtained by histopathology or cytology. PCR may also have potential as a cheap and reliable mass screening diagnostic test. In either event, however, rigorous standardisation and validation will be necessary before a PCR test can be accepted for use in zoning-related QX disease surveillance.