STUDIES ON TRIPLOID OYSTERS IN AUSTRALIA .1. THE FARMING POTENTIAL OFTRIPLOID SYDNEY ROCK OYSTERS SACCOSTREA-COMMERCIALIS (IREDALE AND ROUGHLEY)

A two-and-a-half-year study was conducted to compare the performance o f sibling diploid and triploid Sydney rock oysters Saccostrea commerci alis (Iredale and Roughley) at three intertidal and one subtidal site in Port Stephens, New South Wales (N.S.W.). The triploid Sydney rock o ysters were on average 41% heavier than their diploid siblings after 2 .5 years of growth. The triploid oysters also maintained higher dry me at weight and higher condition index (CI) values than their diploid si blings at all sites during the final 10 months' growth to market size (40 to 60 g whole weight). The triploid oysters at the subtidal site h ad the highest CI values recorded in this study. When exposed to the p rotistan parasite Mikrocytos roughleyi which causes winter mortality d isease, no differences in mortality between diploid and triploid group s occurred. These findings have major implications for the N.S.W. oyst er industry as triploid Sydney rock oysters can reach market size 6-18 months faster and maintain better meat condition than diploid oysters without an increased risk of winter mortality.