The Australian oyster industry is worth $89 million and is the 4th largest aquaculture sector in the country. Of the ~8,500 tons of pacific oysters produced annually, 20-30% are spawnless triploids. With such a large and expanding share of the market it is critical for hatcheries to develop a better understanding of sustainable breeding principles in polyploid oysters. Inbreeding and ways to improve genetics are among a vast array of unknown areas in polyploid oysters. Addressing these issues will provide long term security for the supply of triploid oyster seed to growers around Australia and in the longer term increase profitability via increased production opportunity, growth rate and product quality. As such the project is relevant to the objective of Program 1 - Breeding for Profit.
This work will form the basis to develop the first industry based breeding model to maintain a sustainable population of tetraploid oysters. In addition to this, the project will for the first time provide a model for genetic improvement in triploid oysters and this will yield greater productivity for the industry. Currently, genetic improvement in diploid oysters is fast outpacing that of triploid and this gap could be a risk for the industry in the future. While there are several breeding models available for diploid oysters and other aquaculture species, these do not account for the added genetic complexity of tetraploid oysters. This work addresses the knowledge gap between diploid and triploid oysters to effectively manage and improve polyploid oysters.
Final report
The commercial production of triploid Pacific Oysters (Crassostrea gigas) has grown rapidly in recent years. There is now a push to move away from commonly used mass spawning techniques towards single pair cross selective breeding programs in an effort to improve growth and disease resistance within the triploid product. Before this can be achieved, there is a need to understand some of the fundamental genetics behind polyploid production and to develop molecular tools and techniques that can be used in establishing breeding programs.
This thesis developed and utilised suites of microsatellite markers to determine the baseline diversity of native, naturalised and cultured diploid oysters. It was found that the high diversity within naturalised oysters may provide a genetic reservoir for future breeding programs. The same microsatellite markers were used to determine diversity and pedigree assignment within a mass spawned tetraploid population across two successive generations. The first generation showed a high diversity, which significantly decreased in the second generation produced via mass spawning.
Family selection breeding programs for the production of commercial triploids is the way of the future for the Pacific oyster aquaculture industry. This research provided some of the fundamental information required for the establishment of such a program and developed some of the genetic tools and techniques that will aid in its implementation.
