Paving the way for continued rapid development of the flat (angasi) oyster (Ostrea angasi) farming industry in New South Wales

A diving survey and systematic sampling of live populations of flat oysters was done at 5 locations on the south coast of NSW. These were Merimbula Lake, Pambula Lake, the Bermagui River estuary, Wagonga Inlet at Narooma and the Clyde River estuary at Batemans Bay. At all locations live flat oysters were found on hard substrates projecting above sand, silt or mud sediments or on other vertical substrates especially oyster lease posts and rail structures, jetty piles, natural rocky outcrops and boulders of breakwaters near the mouths of these estuaries. The great majority of live flat oysters collected occurred within a sub-tidal depth band spanning 1 to 4 m below the low water mark. A total of 474 oysters ranging from 80 to 120 mm were collected from the 5 locations. Samples from each oyster were examined to determine their gender, breeding condition and for the presence of disease agents, especially Bonamia that has decimated most wild populations of flat oysters elsewhere in southern Australia and overseas. These and additional flat oysters collected from wild populations in Port Phillip Bay, Victoria, Bicheno, Tasmania, Streaky Bay in South Australia, and Albany, Western Australia, were examined to determine genetic relationships throughout southern Australian distribution of this species. A microscopic parasite, thought to be Bonamia, was detected in wild flat oysters from all 5 southern NSW sites. It occurred in 13% of oysters sampled from Pambula Lake, up to 44% for oysters sampled from Merimbula Lake, with an overall average of 26%. Several other parasites and microbial disease agents were also detected at varying levels. These included a possible viral infection in up to 10% of sampled oysters. Results of the genetics research showed there are little or no differences between populations of flat oysters throughout southern NSW, nor throughout its distribution across southern Australia. Preliminary assessment suggests that the Australian flat oyster is also highly akin to its famous European cousin, the belon oyster. Further investigations into whether Australian and European flat oysters are the same species are underway. The extremely low level of genetic variation detected in this study suggests that the range of the Australian flat oyster has expanded to its current distribution relatively recently in evolutionary terms, perhaps following European settlement. Based on these data, there may be no genetic reason to limit movement of small seed oysters, commonly known as "spat", for culture among estuaries in NSW or to source breeding stock from particular areas to meet local spat requirements. As long as the genetic diversity of broodstock used in hatchery production is high, there should be little or no danger of transporting hatchery produced spat among estuaries in NSW and beyond