Oocyte development and differentiation in pacu, Piaractus mesopotamicus (Holmberg, 1887) (Osteichthyes, Characidae)

Abstract

This work aim is to clarify doubts about the Piaractus mesopotamicus (Osteichthyes, Characidae) oocyte ultrastructural development and differentiation, following the transformations during the ovogenic processes, such as formation and accumulation of various organelles, nucleolar and/or citoplasmic inclusions, and follicular wall (envelope). During the primary growth phase, Balbiani corpuscles are evident, but their role is not clear. The peculiar lamellae structures are also present. The second phase (secondary growth) is initially characterized by cortical alveolus formation. After that, protein yolk granules appear in the peripherical regions, where mitochondria and ribosomes are abundant. Changes in the follicle epitelium (granulosa) are described together with the radiate zone formation, which constitutes the follicular envelope.