Pacific oysters (Crassostrea gigas) are one of the most widely cultivated oyster species in the world, and are farmed extensively in many regions, including Asia, Europe, and North America. In Australia, it is currently one of the largest aquaculture species after Tasmanian Atlantic salmon. Selective breeding has been an essential tool for improving the production and disease management of Pacific oysters in Australia. Australian Seafood Industries (ASI) is an industry-owned selective breeding program focused on increasing resistance to Pacific Oyster Mortality Syndrome (POMS), improving commercial traits (such as meat condition, shell shape, and growth), and increasing overall survival.
Breeding for POMS-resistant oysters began in 2012, with the deployment of existing families from the 2011-year class in New South Wales, Australia. Families specifically selected for POMS resistance were produced for the first time in November 2012 through the spawning of the 2012-year class. POMS outbreak in Tasmania (TAS) disrupted breeding in early 2016. Subsequently, the breeding goal in TAS shifted from adult (12-month-old) to spat (2–3-month-old) POMS resistance. Spat resistance and adult resistance for POMS were similar but not identical traits (0.6 correlation). Trials were conducted using two populations: TAS and South Australia (SA). Research focused on the TAS population as SA farming regions were free of POMS, and trials required exposure to the disease for in-family selection. The trials included ten-year classes (2012-2022), 1502 families, 83 field trials, and over one million individual oysters.
Adult resistance increased from 12% to 100% mean estimated breeding value (EBV), and spat resistance increased from -35% to 67% mean EBV within the TAS population. However, POMS resistance in adults remains a work in progress in SA. In 2022, TAS POMS-resistant stock was bred with SA stock after eight generations of genetic divergence caused by biosecurity barriers. This resulted in increased adult POMS resistance by 24% predicted EBV. The latest commercially available stock, exhibiting high resistance to POMS, has been released for commercial hatcheries, with farmers expected to procure it in the coming year. Further selection is necessary to produce highly resistant brood stock for both spat and adult resistance in TAS and SA. Outcomes to date indicate feasibility and the significance of selective breeding for POMS resistance in safeguarding the industry from potential losses in the future.