Nell J, McOrrie S, Dove M & Perkins B (2007) QX Resistant Oyster Challenge Trial 2005 – 2007. Final Report to Fisheries Research and Development Corporation. Project Number 205/076. NSW Department of Primary Industries. 20 pp.

Summary

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.  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 oyster seed stock produced by commercial oyster hatcheries (single seed). 

In mid 2004, QX disease (Queensland Unknown – QX) 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; highly virulent; and, often results in oyster mortalities in excess of 90%. 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.  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. 

During 2005 a rescue package for the Hawkesbury River oyster industry was developed by NSW DPI that involved; the provision of funds 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 Fisheries Research and Development Corporation the provision of $10,000 to conduct a commercial farm proof of concept trial of QXR SRO.  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 the stock as an alternative oyster crop under normal farming conditions.  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. 

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 marketability of the QXR SRO was demonstrated by the fact that the majority of the stock 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.