Non Technical Summary

Triploid oysters have 3 sets of chromosomes compared to 'normal' diploid oysters which have 2 sets es. Triploid oysters are sterile and grow faster than diploids. Although the commercial benefits of triploidy have been evaluated in the Pacific oyster Crassostrea gigas, eastern oyster C. virginica, Sydney rock oyster Saccostrea glomerata and European flat oyster Ostrea edulis, so far this technique has only been commercialised for Pacific oysters.

Commercial production of triploid oysters on the West Coast of North America began in 1985 and has greatly increased since then. The tetraploid (4 sets of chromosomes) males have now been used to fertilise eggs from diploids to produce batches of 100% triploids. In 1999/2000 triploid Pacific oysters made up 30% of all Pacific oysters farmed on the West Coast of North America. Most of these were produced using sperm from tetraploids to fertilise eggs from diploids, instead of using older chemical methods of induction.

Triploid Sydney rock oysters reach market size (40 - 60 g) 6 months earlier than the usual 3½ years for diploids, hold their meat condition longer in autumn and winter and death from winter mortality is reduced by more than half. A slight brown discolouration of the gonad has been noted in some triploid Sydney rock oysters. However, this is less noticeable during the cooler months of winter and spring when the superior condition its of triploids over diploids make them most useful to oyster farmers. Unfortunately these excellent results with Sydney rock oysters cannot be commercialised until current problems with hatchery production are overcome.