O'Connor, S., O'Connor, W., Bolch, C. and Moltschaniwskyj, N., 2011. Advances in hatchery production of flat oysters Ostrea onyosi. Presentation given at the 4th International Oyster Symposium, 15 – 18 September 2011, Hobart, Tasmania.

Summary

Increased domestic demand coupled with potential export markets has renewed interest in farming of the native flat oyster, Ostrea angasi, in the southern states of Australia. But low numbers and unreliable wild catch of native flat oyster spat has meant the flat oyster industry has become reliant on hatchery produced spat. One important economic development has been the hatchery production of single seed or culchless oyster spat (spat that are not attached to a substrate).

During the early stage of an oyster life cycle, oyster larvae are free swimming for several weeks before changing to an oyster spat and settling on a suitable substrate. This transformation from swimming to benthic (i.e., bottom dwelling) is termed metamorphosis. To produce single seed spat from the hatchery, several chemicals were investigated to see if they could induce metamorphosis of O. angasi larvae without the resulting spat attaching to a substrate. Treatment of O. angasi larvae with 10-3 M epinephrine bitartrate or 10-4 M epinephrine for 1 h was successful in producing single seed spat and has been adopted for routine commercial production.

Epinephrine was then used as a “tool” to examine the effects larval rearing conditions on larval development. The effect of different algal diets, temperature and salinity on survival, growth and development of larvae was investigated. Algal diets composed of Isochrysis sp. (T. Iso) and Tetraselmis chuii in combination with either P. lutheri or N. oculata promoted the greatest larval growth, survival and development. Optimal larval growth, survival, and development was observed at temperatures of 26 – 29oC and salinities of 30 – 35. Studies are now underway to better understand catecholamine settlement induction.

Additional improvements in hatchery production have also been achieved by quantifying the seasonal availability of larvae at 4 sites on the NSW coast (Merimbula Lake, Bermagui River, Wagonga inlet and Gogleys Lagoon). Variation in the length of the spawning season was evident, with the northern most location having brooding oysters (i.e., oysters retaining larvae) for the longest duration. The use of magnesium chloride to “anesthetise” both oysters and any larvae they may be retaining has meant larvae can be routinely collected from sites up to 12 h travelling time away and brought to the hatchery for culture.