By W.A. O’Connor, D.A. Raftos, M.C. Dove, A. Kan & K. Johnston
The New South Wales Sydney Rock Oyster (SRO) industry has undergone major structural change in the past five years that has seen it begin the adoption of selectively bred SRO hatchery seed and establish a company (Select Oyster Company; SOCo) to manage commercialisation of the oyster breeding program. This study worked with SOCo to address the problem of QX disease in SRO. QX is a disease caused by the parasite Marteilia sydneyi and affects SRO causing loss in oyster condition and, in later stages of the parasite development, causes death of infected oysters. Investigations of oysters surviving QX outbreaks indicated that the particular enzyme, phenoloxidase (PO), is associated with disease resistance and that suppression of this PO activity leads to disease susceptibility.
This study also characterised the PO enzyme in SRO and showed that a precursor, proPO, exists in oyster hemocytes (blood cells) can be activated to become PO. Then the link between PO and QX disease resistance was shown, illustrating that PO is a critical component of the cellular defences of oysters against infection by Marteilia sydneyi. Among the 60 family lines produced in this study, 30 families were created from crosses within and between QX resistant (QR) and non-selected wild type (WT) oysters. When these families were grown in a QX disease prone area, oysters from QR × QR crosses had significantly lower mortality compared to QR × WT or WT × WT families.
Cryopreservation of gametes (eggs and sperm) is a valuable tool for breeding programs that has a number of potential benefits. Cryopreserved gametes can be used to improve hatchery operations by providing eggs or sperm on demand, eliminating the need to maintain live broodstock. This study assessed the potential for cryopreservation of SRO gametes. Reliable protocols for the cryopreservation of sperm were developed and a Standard Operating Procedure has been incorporated in the SOCo practical operations manual. Batches of SRO D-larvae, large enough for family line production, have been produced using cryopreserved sperm and successful cryopreservation of SRO eggs was also achieved.