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viewed as the 'gold standard' for QX disease diagnosis, while preliminary comparative data (Callinan and Wesche, unpublished data) suggest that an alternative cytological method, stained tissue imprints of oyster digestive gland, has a sensitivity of 60% and specifically of 100%.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.