Fertilization of the eggs of bivalve mollusks with different insemination conditions.

Eggs of the bivalve mollusks Ostrea gigas, Spisula sachalinensis, and Mactra sulcataria taken from the ovary and placed in sea water are capable of maturation: the nuclear membrane dissolves and polar body I is released. The percentage of such spontaneously ripening eggs differs widely in different females and apparently characterizes the degree of roe maturity. The fertilization rate of roe containing a small percentage of spontaneously maturing eggs increases considerably during holding in sea water and remains at a high level for several hours. Maximum percentage fertilization can be obtained only over a narrow range of sperm concentrations in suspension for the species studied. A concentration of 10-6 or 10-7 sperm/cm-3 is usually optimum; a decrease or increase in sperm concentration by an order of magnitude (in comparison with the optimum level) reduces percentage fertilization. It was shown that sperm in suspensions with concentrations above the optimum level are activated to a lesser extent and their speed of movement is less than at high dilutions.