Proportion of sperm and eggs for maximal in vitro fertilization in haliotis asinina and the chronology of early development

Abstract

To obtain the highest yield during in vitro fertilization of tropical abalone Haliotis asinina, optimal proportion of the gametes, the timing of sperm-egg interaction, and subsequent development were investigated. The highest yield of fertilization (75%) with fewest abnormal eggs was obtained when incubating eggs and sperm at the ratio of 1:100 in seawater with a salinity of 27.5 ppt, a pH of 7.8, and a temperature range from 2729°C. After incubation, sperm swim through the eggjelly coat and become bound to the vitelline envelope within 30 sec, followed by an acrosomal reaction at 1 min. The fertilized egg extrudes the first and second polar bodies at 810 min, and then the zygote begins cleavage at 1520 min. This is followed by the second cleavage, and development through the stages of blastula, gastrula, trochophore, veliger, and early creeping larvae, which were completed within 3 days. Noticeably, occurrence of egg jelly condensation after penetration of the first sperm would not allow other sperm bind to the egg jelly and to penetrate through its vitelline envelope. This event is thought to be a weak blocking against polyspermy, because the classic cortical reaction initiated by cortical granule exocytosis could not be observed in this species.