The early life stages of the growth of bivalve molluscs being now controlled, at least for oysters and clams, it is possible to obtain seeds in large amounts and at given times. Reproduction may be obtained at any period of the year and the survival rates range from 5 to 50 % these values being considerable compared to those of natural reproduction in the sea. However the cost of the spat increases very sharply with size because of energy input (heating, pumping and phytoplancton production).