Formation of zona radiata and ultrastructural analysis of egg envelope during oogenesis of Chinese perch Siniperca chuatsi.

During oocyte maturation, egg envelope undergoes a series of changes in structure and function. We investigated the follicular envelope, zona radiata and plasmalemma of Chinese perch, Siniperca chuatsi at five different developmental stages by light, scanning and transmission electron microscopy. An octopus-like structure in the zona radiata was observed for the first time. The increasing thickness of zona radiata during these stages suggests the microvilli's functional transition from transferring vital materials for the protection of the oocyte. That the egg envelope fully matures later than the oocyte is well supported by the disappearance of the follicular envelope. We have discovered several characteristic structures in the semi-floating egg and propose that the octopus-like structure is essential for oocyte migration and fertilization.

Ultrastructural observation on genesis and morphology of cortical granules in Macrobrachium nipponense (Crustacea, Caridea).

Cortical granules are secretory vesicles in oocytes that develop from the Golgi complex. In the freshwater shrimp, Macrobrachium nipponense, mitochondria participates in the formation of cortical granules. We investigated the structural changes of mitochondria and the distribution cortical granules in different stages of oocyte development. Transmission electron microscopy provided evidence for the involvement of mitochondria and a particular spiral lamellar organization and an electron-lucent area in internal cortical granules. The ooplasm provided material for the cortical granules in early oocyte development. We demonstrated that mitochondria play a role in coalescence and maturation of cortical granules in this species. Additionally, a concept of cortical granules regarded as a functional integration is put forward. The genesis of shrimp cortical granules exhibited a particular pathway of maturation. The outer shape and inner organization considering different taxa suggested general as well as specific features of the development of cortical granules.