Morphological alterations of all stages of spermatogenesis and acrosome reaction in Chinese mitten crab Eriocheir sinensis.

The Chinese mitten crab (Eriocheir sinensis) is a seasonally breeding species and its reproductive system comprises paired symmetrical structures: testes, vasa deferentia, seminal vesicles, accessory glands and ejaculatory ducts. Histological examination of the testis of mature males reveals regression of the gonads and inhibition of the process of spermatogenesis during December to April of the following year, the regeneration of the gonads during June to July and the occurrence of the highest level of spermatogenesis during August to October. Microscopic assessments and hematoxylin and eosin (H&E) staining were used to describe all spermatogenic stages (spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoids). To observe the morphological changes during spermiogenesis, we successfully initiated primary cell culture using testis tissue of E. sinensis, which will lay a solid foundation for further work on the immortalization of crab cells. During the interaction between the sperm and oocyte, the fertilizing spermatozoon must undergo a series of terminal morphological changes, called the acrosome reaction (AR). This study also provides a detailed description of the structural alterations of the acrosome reaction of E. sinensis. The acrosome complex and cup-shaped nucleus are located at the anterior and posterior of the spermatozoon, respectively. Male germ cell development involves a tightly controlled sequence of differentiation switches. The purpose of this study is to increase our knowledge of the morphological alterations during spermatogenesis and the acrosome reaction, whose changes are a fundamental requirement for fertilization of E. sinensis.