The Hawkesbury River is located approximately 50 km north of Sydney NSW. In 2003, the Hawkesbury River was the third largest Sydney rock oyster Saccostrea glomerata (SRO) producing estuary in NSW, with an annual farm gate production of $3.6M (10.1 million oysters).

The commercial production of SRO in the Hawkesbury River was based exclusively on the traditional intertidal stick and tray method of oyster farming.  This method of oyster production is reliant on the annual settlement of SRO larvae that occurs towards the mouths of estuaries during the summer and autumn months.  To take advantage of this natural oyster settlement, oyster farmers placed tar and cement coated oyster sticks on intertidal timber racks in early summer in areas known for reliable SRO settlement.  The following spring the oyster sticks caught with wild spat (juvenile oysters) are moved upstream to be on-grown on intertidal racks in areas away from further competing SRO settlement. Once the SRO have reached a suitable size they are removed from the oyster sticks by hand and placed on timber, mesh bottom, trays and returned to the growing areas where they remain until they reach a marketable size of around 50g whole weight (approximately 3.5 years of age).

Due to the high productivity of the waters of the Hawkesbury River and the historical reliability of the stick and tray method of production, Hawkesbury River oyster farmers had not seen any need to move away from their traditional farming methods towards single seed oyster farming technology that would enable them to take advantage of oyster seed stock produced by commercial oyster hatcheries.  Before 2003, hatchery production of commercial quantities of SRO was unreliable.  Hatchery production of SROs commenced in the early 1980s but has been plagued by recurrent mass mortality (>80%) of larvae and spat.  A Fisheries Research & Development Corporation (FRDC) project (Number 2003/209) commenced in 2003 with the aim of overcoming constraints to commercial scale hatchery production of SRO and developed techniques that have resulted in commercial hatcheries supplying the SRO industry with spat that are selectively bred for faster growth and disease resistance.

In mid 2004, QX disease was detected in the key major upstream SRO commercial oyster harvest areas in the Hawkesbury River.  QX disease, which is specific to the SRO, is: caused by the protozoan parasite Marteilia sydneyi (Wolf, 1979); highly virulent; and, often results in oyster mortalities in excess of 90%.  QX has led to the collapse of commercial oyster cultivation in a number of areas in NSW and southern Queensland.  Due to the poor visual meat condition of QX affected Hawkesbury River oysters and adverse publicity surrounding the disease outbreak, commercial sales of Hawkesbury River oysters quickly ceased.  By mid 2005, QX disease surveillance conducted by the NSW Department of Primary Industries (NSW DPI), in cooperation with Dr Rob Adlard of the Queensland Museum, indicated that the disease causing QX parasite had spread throughout the majority of the commercial farming areas in the Hawkesbury River system.  By this time most farmers were in serious financial difficulties and were retrenching staff.  Given the history of QX outbreaks in other estuaries, the Hawkesbury River oyster industry quickly recognised that oyster production based on the wild QX susceptible SRO was no longer viable.

Since the mid 1990’s, NSW DPI has been developing a breeding line of SRO that has been selected for fast growth and has demonstrated good resistance (>75% survival) to outbreaks of QX disease on commercial oyster leases under experimental conditions in the Georges River NSW (Nell and Perkins, 2006).  However, the commercial viability of this breeding line of QX resistant (QXR) SRO under Hawkesbury River commercial farming conditions was unknown.  Hawkesbury River farmers also expressed concern regarding the unknown marketability (i.e. possible poor visual meat condition) of the QXR SRO stock should it be grown in the heavily QX infested areas in the Hawkesbury River. They also had concerns as to their individual financial ability to invest in single seed technology which they believed was unproven under Hawkesbury River oyster farming conditions.

During 2005 a rescue package for the Hawkesbury River oyster industry was developed by NSW DPI that involved; the provision of $2,700,000 available to Hawkesbury River oyster farmers to assist them to remove and dispose of dead and dying stock and collapsing oyster encrusted infrastructure from their leases; and in cooperation with FRDC the provision of $10,000 to conduct a commercial farm proof of concept trial of QXR SRO developed under FRDC Project (Number 96/357).  Following a favourable environmental impact assessment, approval was also granted to Hawkesbury River oyster farmers to import and cultivate triploid Pacific oysters directly from the controlled environment of a Tasmanian commercial oyster hatchery.  Under the proof of concept trial, NSW DPI has made available approximately 200,000 QXR SRO spat to seven Hawkesbury River oyster farmers who expressed interest in an evaluation of the suitability of QXR SRO as an alternative oyster crop under normal farming conditions.  The spat were supplied to participating farmers in specialised single seed oyster trays developed and supplied by NSW DPI.  NSW DPI also provided ongoing technical advice and field assistance regarding the maintenance of the spat on commercial leases until the oysters could be transferred to traditional oyster growing tray systems used by oyster farmers.  Concurrently, NSW DPI maintained QXR SRO at three key QX infection sites with the cooperation of farmers.  

The QXR SRO were exposed to two consecutive QX infection events.  The QXR SRO demonstrated excellent survival and growth and maintained good marketable condition under both experimental and normal Hawkesbury River farming conditions.  The observed QXR oysters’ resilience to QX infection was reinforced by the fact that the QX parasite was not detected in the digestive gland of any of the oysters examined following visual meat condition assessments undertaken by Hawkesbury River oyster farmers following the QX infection events.  The marketability of the QXR SRO was demonstrated by the fact that the majority of QXR SRO held on prime Hawkesbury River fattening leases by participating farmers were sold by 24 months of age.  Participating farmers also had no difficulty in adopting small single seed management practices prior to transferring stock to the traditional tray growing technology used in the Hawkesbury River.  Hawkesbury River oyster farmers were also able to apply the principals of small single seed oyster management to the development of a flexible and cost effective floating bag single seed system for use on their leases. 

Keywords: Saccostrea glomerata, Marteilia sydneyi, QX, disease resistance, oyster, commercial production.