Were are two main reasons for the development of cultivation techniques of new bivalve species. First, the risk exists that traditionally reared species may be ereadicated or severely depleted by pathogenic agents. For example the Portuguese 0yster Crassostrea angulata. disapeared from the French coasts in the early 1970's and worldwide production of the flat oyster, Oslrea edulis has been dramatically reduced by the effects of Bonamia. Secondly, in some countries production may he self-Iimiting by the size and availabilily of national and international markets and a wider species range could offer some promising new economic opportunities for aquaculturists. In particular this applies to species where there are identifiable market shortfalls.