Pearl oyster farming is one of Australia's most successful aquaculture industries, with substantial scope for future growth. Recent data suggest that the pearling industry generates approximately $100 m pa and provides significant employment opportunities in remote areas of Australia. Despite its remarkable success, the viability of Australian P. maxima pearling is compromised by a fatal disease (oyster oedema disease, OOD). If OOD is not controlled, the industry is unlikely to develop as efficiently and cost effectively as required. In some areas, the disease is making it difficult to restock growing areas with hatchery reared spat, and it is significantly decreasing the number of oysters available to produce pearls. OOD also appears to be impacting wild P. maxima populations.
The proposed project is the first step in developing an integrated management strategy to control OOD in the Australian pearling industry. Some progress has been made in studying the disease. We suspect that OOD is initiated by an infectious virus associated with secondary bacterial infection. But we still do not understand:
1. the precise causative agent(s) of OOD, or,
2. how to provide early diagnosis of the disease
These gaps in our knowledge mean that industry does not have sufficient information to establish effective management strategies that can control OOD. Most importantly, we need diagnostic methods to detect the onset of disease before catastrophic outbreaks occur. Such tests could be used to identify disease-free broodstock for hatcheries, find areas where OOD is less prevalent, determine environmental factors that might be associated with infection, and manage the translocation of OOD-affected oysters. Our project addresses these needs in order to identify management practices that can be used to control OOD and secure the Australian pearling industry.
Final report
The goal of this project was to investigate the cause of oyster oedema disease (OOD) in Australian pearl oysters so that diagnostic tests and management practices for the disease can be developed. OOD has been associated with mortalities in some pearl oyster farming areas. However, the cause of these mortalities has remained unknown, hampering efforts to study the disease and develop effective control strategies. The project described in this report was conducted by researchers from Macquarie University, Fisheries Western Australia and the New Zealand Ministry for Primary Industries (Manatū Ahu Matua), working in collaboration with the Australian Pearl Producers Association and the Australian pearling industry. We compared OOD-affected oysters with healthy control oysters to identify any genetic material in the OOD-affected oysters that might come from an infectious agent such as a virus, bacteria or parasite. Our logic was, if OOD is caused by an infectious agent, genetic material (cDNA nucleotide sequences) from that infectious agent should be far more abundant in OOD-affected oysters than in healthy controls. That genetic material would act as a fingerprint for the disease and may provide information about its cause. We found clear differences between the nucleotide sequences present in oysters affected by OOD when compared to healthy controls. A number of nucleotide sequences were strongly associated with OOD and the abundance of some of these sequences was correlated with increasing mortality. None of these nucleotide sequences were closely related to any known infectious agents. However, the strong relationship between these sequences, OOD and mortality means that they may be very useful predictors of mortality. Their lack of resemblance to known infectious agents leaves open the possibility that OOD is not an infectious disease and may have some other cause.
