Zosterisessor ophiocephalus is subject to remarkable fishing effort even during the reproductive period. Therefore, basic knowledge of its biology is an essential preliminary to any attempt to manage either natural or artificial reproductive stocks. This study is meant to provide a basis for identifying reproductive stages and for relating them to the natural seasonal cycle or to the effect of treatments for promoting maturation. Oocyte staging was performed on conventional thick and TEM sections. Previtellogenic, vitellogenic and maturative stages were further subdivided according to the classic criteria such as meiotic chromosome pairing, nucleus and nucleolus appearance and position, Balbiani's body formation, occurrence and storage of yolk granules as summarized in Table I. Development of theca and granulosa cells was also taken into account. Attaching filament formation and chorionic micropylar specializations are described by TEM and SEM. The results are compared with a previous approximate LM description in this species and with the more recent ultrastructural features reported in gobies and in other teleosteans.
