Observations on the Spermatozoon, Egg and Fertilization Process of Centropristis striata Using the Electronic Microscopic Technique

Abstract:

To explore the fertilization mechanism of Centropristis striata and improve the fertilization rate, the ultrastructure of spermatozoon and egg and the fertilization process were observed using the scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the sperm of C. striata was mainly composed of the following three parts: 1) head; mainly consisted with nucleus and without the acrosomal structure; 2) midpiece; consisted with mitochondrion, centriolar complex (including proximal centriole and matrix) and sleeve structure; and 3) tail; consisted with axoneme that is surrounded by plasma membrane. The axoneme of C. striata was consistent with the typical “9+2” structure in most fish. The eggs were spherical, colorless, and transparent with the diameter at (0.950±0.039) mm, which belonged to pelagic eggs. A big grain of oil ball (0.182 ± 0.011mm in diameter) was observed in the egg. Overlapping curves were observed on the surface of the eggs, on which the tiny holes with different sizes (0.246±0.103 µm) were evenly distributed. A completely-opened fertilization hole was in the central part of the funneled area at the animal pole. The shell of the egg included plasma membrane, vitelline membrane and shell membrane. The shell was filled with cytoplasm. The fertilization process of C. striata was short. The sperm penetrated into the egg through the micropyle in 10 seconds after insemination. The morphological feature of the fertilized egg changed after that, and the fertilization cone and fertilization plug were observed. Finally, about 60 s after insemination, the fertilization hole closed to prevent the penetration of other sperms. This study may provide theoretical foundation to improve the fertilization rate of C. striata artificial breeding.