Paving the way for continued raid development of the flat (angasi) oyster (Ostrea angasi) farming industry in New South Wales
|Paving the way for continued rapid development of the flat (angasi) oyster (Ostrea angasi) farming industry in New South Wales
This project aimed to help continued expansion of flat oyster (Ostrea angasi) farming in NSW. The value of this new and emerging industry is about $100,000 per annum. Flat oysters, also known as angasi, bluff, mud and belon oysters, are being farmed alongside Sydney rock oysters on the south coast of NSW. These oysters reach market size in about 18 months or half the time of Sydney rock oysters. They are also receiving a high farm-gate price of about $9 per dozen and are the preferred traditional oyster of people from Western Europe, Asia and New Zealand.
Seed from flat oysters have been supplied to farmers by the NSW Fisheries oyster hatchery at Port Stephens over the past 5 years from breeding stock collected from the wild. This project tackled two major concerns to continued expansion of this industry. The first is a disease called Bonamia that has devastated flat oyster fisheries and farming elsewhere in Australia and the rest of the world. The second is possible genetics problems linked to the use of hatchery-produced seed.
To assess the incidence of Bonamia disease, diving surveys were made of wild flat oyster populations at five locations on the south coast of NSW. Flat oysters were collected from hard substrates projecting above sand, silt or mud sediments or from other vertical substrata, especially oyster farm structures, jetties and natural rocky out-crops, walls and breakwaters, all within a band 1 to 4 metres below the low tide mark. Collections of wild oysters were made at each location in April 2003 to coincide with the highest likely presence of Bonamia infections. A total of 474 oysters were collected: 88 from 7 sites at Bermagui; 102 from 6 sites at Merimbula; 98 from 7 sites at Narooma, 94 from 6 sites at Pambula and 92 from 3 sites at Batemans Bay. Samples of tissues were taken from each oyster. Preserved tissue samples were then sent for expert examination for Bonamia infection and other aspects of their general health and condition. A microscopic parasite, thought to be Bonamia, was detected in an average of 26% oysters from the five locations. The minimum and maximum rates recorded were 13% of oysters collected at Pambula and 44% of oysters from Merimbula. Continued research will confirm the identity of Bonamia and will fast-track the development of a new molecular test for diagnosing Bonamia.
Tissue samples of oysters were used to determine the genetic relationships of the flat oyster throughout its southern Australian range. Results showed that flat oysters are almost identical regardless of where they occur in a range that stretches from southern Queensland, around the southern seaboard of Australia including Tasmania, to the Swan River in Western Australia. Even more surprising is that the Australian flat oyster is probably identical to its 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 suggests that the range of this species has expanded to its current distribution relatively recently in evolutionary terms, perhaps since European settlement, and that dispersal and genetic mixing is widespread. If these results and interpretations are correct, there is no reason to limit translocations of spat among estuaries in NSW or to source breeding stock from particular areas to meet local requirements. As long as the genetic diversity of brood-stock used to produce seed oysters in hatcheries is high and the seed are free of serious disease, there appears to be little danger in moving their offspring between estuaries in NSW and beyond.