Executive Summary

Hatchery, nursery, farming and post-harvest handling techniques used to produce flat oysters in central and southern NSW over the past three years and in Port Phillip Bay, Victoria between 1986 and 1992, were reviewed in some detail.

Practical experience to date is that there are few if any serious technical barriers to reliable production of seed juveniles. Flat oysters can be grown to optimum domestic and European export market size of 70 mm (80 g) in one and a half to two years in inter-tidal tray culture, and perhaps less in floating trays as demonstrated at Bermagui or suspended deep water culture as demonstrated in Port Philip Bay. Optimum growing height for inter-tidal tray culture on existing leases is indicatively 25 to 30 cm below that of Sydney rock oysters. Flat oysters grown this way have shown low susceptibility to mud worm and bio-fouling especially if air dried in the shade for two to three days each month during the high bio-fouling season from late Spring (November) to late Autumn (May).

By far the greatest difficulties encountered to date by the eleven NSW oyster growers involved in trial farming of flat oysters has been post harvest and marketing problems. Foremost of these has been very short (two to three days) shelf life when handled the same way as Sydney rock oysters, highly variable meat quality between consignments and presence of gravid black-sick and grey-sick brooders among consignments as far apart as June and February. Major factors known to reduce flesh quality are farming protocols, especially; growing height, excessive stocking densities and bio-fouling occlusion of mesh, in tray and basket reared oysters and seasonal factors especially spawning and low temperatures.

Bonamiasis was clearly exposed as the greatest potential risk to the long-term sustainability of flat oyster farming and to the export potential of this species. However off-bottom culture and harvesting of flat oysters prior to first spawning were identified as possible ways to minimise these risks. Likewise, surveys to identify disease-free production areas, certification of these areas and adoption of farming techniques involving quality assurance programs to safeguard the health of consumers were identified as possible ways of overcoming barriers to export.

Although flat oysters will need to compete against locally produced and imported rock oysters they do have a competitive edge in appearance and greater apparent potential for export. The most important marketing message was the need for growers (not marketers) to collectively develop and ensure orderly marketing of flat oysters that are safe for consumers, are of a standard size and uniform good flesh quality and go by a single universally recognised and attractive name such as Angasi or Belon. The next most important factor is the adoption of long shelf life packing and chilled storage methods already developed and documented by the Marine and Freshwater Research Institute (MAFRI) in Victoria.