Effects of gamete concentration on the in vitro fertilization of manually extracted gametes of the oyster ( Crassostrea rhizophorae)

A number of experiments were undertaken to better understand and characterize the effects of different gamete concentrations on the efficiency of in vitro fertilization in Crassostrea rhizophorae. Maximum fertilization efficiency was achieved with a broad range of sperm concentrations, thus minimizing the importance of sperm concentration in successful in vitro fertilizations. However, a linear and inverse relationship was found between egg concentration and fertilization efficiency. This suggests that egg concentration is an important parameter for successful in vitro fertilizations. No evidence was found to support oxygen depletion or the physical crowding of eggs as the cause for the deleterious effect of high egg concentrations. The deleterious effect was counteracted by continually washing the fertilized eggs, suggesting the presence of a water-soluble substance, originating from the zygote, as the cause of the egg effect. In addition, maximizing the total number of viable larvae/ml was found not to be strictly correlated with fertilization efficiency. Lastly, support is presented for the use of concentrations, instead of ratios, in determining optimal gamete numbers.