The NSW oyster industry has suffered from QX disease and winter mortality for a very long time. It has responded to these disease challenges by vacating affected leases seasonally or in the case of Georges River by abondoning the infested part of the estuary. The history of inter-estuary transfer of oysters for on-growing has not allowed the development of resistant strains in NSW. However, if resistant strains of oysters are not developed, the industry will have no better management tool available in future than that used in the past, ie moving or selling oysters before a disease outbreak is expected or abondoning oyster leases.
If the opportunity for breeding QX disease resistance in Sydney rock oysters is not taken up, a unique opportunity will be lost, to use breeding lines previously selected for fast growth in the selection for disease resistance. It is important that breeding for QX resistance begins now, before another estuary is infested with this parasite. In Georges River, the industry responded to the QX outbreak by abandoning affected leases.
Growth rates in Sydney rock oysters have been improved by an average of 4% for the first generation of selection in Port Stephens. Now the initial progress has been made and four breeding lines are established, it is important that the momentum is maintained and selective breeding for fast growth is continued. The growth rate of the Port Stephens selection lines can be increased by 4% for each successive generation.
Growth rates in Sydney rock oysters can be improved by both selective breeding (an average of 4% faster growth for the first generation of selection) and triploidy (30-40% faster growth). However, triploids have not previously been produced from improved breeding lines. It is important to determine if improvements in growth rates by these two methods are additive. For example with triploids produced from improved breeding lines, a 30% increase in growth rate with triploidy plus another 8% for two generations of selective breeding may increase growth rates of oysters by 38%.
