Potential for genetic improvement of Sydney rock oysters ('Saccostrea glomerata')

Abstract

Since 1990, Sydney rock oysters (SRO: 'Saccostrea glomerata') have been successfully selected for fast growth and resistance to the two major SRO diseases; QX disease and Winter mortality in a mass selection breeding program operated by the NSW Department of Primary Industries and Fisheries (DPI&F). However, these are not the only traits of economic importance to SRO farmers and their customers, thus a survey was conducted to establish which traits are of importance to their businesses. Weighted totals from survey results indicated that, in decreasing order of importance, growth rate, meat condition, shell shape, general mortality, WM resistance, QX resistance, meat colour, appearance and eating quality were all considered to be traits of importance to SRO farmers. In comparison, wholesalers did not consider factors that did not directly affect their business (e.g. growth rate or mortality) as important but regarded meat condition, shell shape, meat colour, presentation and size as important factors affecting their operation. Survey results also included production and economic (returns and variable costs) data. Strategies were developed to estimate the economic values for the first seven traits reported above, using this data. Economic values have not previously been available for SRO traits, possibly because industry standards for measuring traits are largely absent. Consequently, trait genetic parameters are also largely unknown for SROs, compounded by difficulties in achieving planned mating structures to ascertain these parameters. Nevertheless, after assumption were made regarding trait measurement procedures and parameters, the relative importance of traits were established by multiplying the calculated economic values by the assumed genetic standard deviation (GSD) for each specific trait. Economic values were derived on a dollars per dozen basis for each one unit change of the trait expression. Mortality due to QX and WM were the most important traits ($2.72/GSD and $1.13/GSD), followed by growth rate (average $0.70/GSD), meat condition ($0.56/GSD), shell shape ($0.016/GSD) and strength (average $0.018/GSD). Since the measurement of meat condition, an important trait, is typically destructive, strategies will need to be developed to measure condition on live animals for mass selection. Alternatively, improvements in hatchery reproductive performance are required to generate family structures for developing more sophisticated breeding programs, whereby sacrificed relatives can provide some of the necessary data.