Histological and Ultrastructural Studies of Ovarian Development and Micropyle Structure of Zebra Sea Bream Diplodus cervinus cervinus (Lowe, 1838)

This study was designed to assess the histological and ultrastructural stages of the female sparid, zebra sea bream (Diplodus cervinus cervinus) sexual maturity, while publications that paid attention to the reproductive biology of this protandrous species is almost lacking. In the present study, it is suggested that oogenesis is classified into four stages: oogonia proliferation (the presence of oogonia is a typical feature of this stage), oocyte growth (is characterized by the formation of follicular layers around the oocyte. large nucleus and scattered nucleoli), vacuolization (is described by the appearance of marginal vacuoles) and final maturation (in which ovaries decreased in size, appeared with collapsed features, exhibited empty follicle and were provided with many blood vessels). D. cervinus cervinus is a partially ovipositing species having a multiple spawning character with asynchronous oocyte development. Transmission electron micrographs of the ripe oocyte demonstrated that it was characterized by the appearance of five ideal ovarian layers (theca, follicular epithelial, zona radiata externa, zona radiata interna and cortical alveoli). In teleost fish, eggs allow the entry of sperm from only a single site known as `the micropyle`, which is a narrow canal in the chorion of the egg. The morphology and classification of Diplodus micropyle were also investigated by scanning electron microscopy. During the spawning season, the full-grown Diplodus eggs collected from adult gravid females possess a single micropyle at the animal pole. This micropyle is a conical shaped with no pit, characterized by a tapering opening having only a deep, constricted canal. Several thickened annuli with little knobs strengthened the inside of the canal. In conclusion, this study provides a comprehension on the reproductive biology of D. cervinus cervinus which is important for the culture and sustainable seed production of this species.