Stages of oocyte development in the pipefish, Syngnathus scovelli.

Oocyte development occurs in a temporal and spatial pattern in the ovary of the pipefish, Syngnathus scovelli. Cytological observations combined with [3 H]thymidine uptake and cell culture were used as criteria to identify six stages of oocyte development in this species. Stage I-Oogonia, found within the germinal ridge. Stage II-Oocytes in primary growth, subdivided into (1) chromatin-nucleolus oocytes in early prophase I of meiosis, also found within the germinal ridge, and (2) perinucleolar oocytes, which possess multiple nucleoli and are within definitive follicles (the Balbiani vitelline body is the main cytoplasmic component in these latter oocytes). Stage III-Oocytes distinguished by the appearance of cortical alveoli, the vitelline envelope, and lipid. Stage IV-Vitellogenic oocytes, which accumulate yolk proteins and possess primary, transitional, and mature yolk spheres. Stage V-Maturational oocytes, which are competent to undergo final meiotic maturation in vivo and in response to the steroid 17 α-hydroxy-20β-dihydroprogesterone in vitro. Stage VI-Ovulated mature eggs, which are present in the ovary lumen and are capable of being fertilized. These studies provide a staging series for oogenesis and oocyte development in the pipefish and relate these stages to the unusual ovary in this animal.