Oogenesis: From Oogonia to Ovulation in the Flagfish, Jordanella floridae Goode and Bean, 1879 (Teleostei: Cyprinodontidae)

Abstract

We provide histological details of the development of oocytes in the cyprinodontid flagfish, Jordanella floridae. There are six stages of oogenesis: Oogonial proliferation, chromatin nucleolus, primary growth (previtellogenesis [PG]), secondary growth (vitellogenesis), oocyte maturation and ovulation. The ovarian lamellae are lined by a germinal epithelium composed of epithelial cells and scattered oogonia. During primary growth, the development of cortical alveoli and oil droplets, are initiated simultaneously. During secondary growth, yolk globules coalesce into a fluid mass. The full-grown oocyte contains a large globule of fluid yolk. The germinal vesicle is at the animal pole, and the cortical alveoli and oil droplets are located at the periphery. The disposition of oil droplets at the vegetal pole of the germinal vesicle during late secondary growth stage is a unique characteristic. The follicular cell layer is composed initially of a single layer of squamous cells during early PG which become columnar during early vitellogenesis. During primary and secondary growth stages, filaments develop among the follicular cells and also around the micropyle. The filaments are seen extending from the zona pellucida after ovulation. During ovulation, a space is evident between the oocyte and the zona pellucida. Asynchronous spawning activity is confirmed by the observation that, after ovulation, the ovarian lamellae contain follicles in both primary and secondary growth stages; in contrast, when the seasonal activity of oogenesis and spawning ends, after ovulation, the ovarian lamellae contain only follicles in the primary growth stage. J. Morphol. 277:1339-1354, 2016. © 2016 Wiley Periodicals, Inc.

Ovarian structure, folliculogenesis and oogenesis of the annual killifish Millerichthys robustus (Cyprinodontiformes: Cynolebiidae)

“…The germinal epithelium of M. robustus was observed to be active as indicated by the presence of oogonia in mitosis, distributed along or in cell nests as reported by Lo Nostro, Grier, Andreone and Guerrero () in Synbranchus marmoratus ; Grier, Uribe and Parenti () in Oncorhynchus mykiss ; in Jordanella floridae (Uribe et al, ) and formation of primary oocytes in CN stage with the beginning of meiosis, coinciding with that mentioned by Grier () and Grier et al (). Our results show that folliculogenesis in M. robustus was completed after the synthesis of the cortical alveoli in the oocytes when these oocytes also have nucleoli around the germinal vesicle periphery.…”

“…During primary growth (PGod) of M. robustus , abundant oil droplets in the ooplasm were seen similar to those described in F. heteroclitus (Wallace & Selman, ) , Crenichthys bailey , Empetrichthys latos (Uribe, Grier, & Parenti, ) and Jordanella floridae (Uribe et al, ). The inclusion of oil droplets in the oocyte is associated with the increment of insulin‐like growth factor (IGF‐1), and derived molecules of FSH and E 2 .…”

“…The female reproductive system of M. robustus is similar to those described for most other teleosts, consisting of two ovaries of cystovarian condition (Yamamoto & Yamazaki, ; Nagahama, ; Devlin & Nagahama, ; Uribe, Grier, García‐Alarcón, & Parenti, ). The gonoduct was identified as having a similar morphology as described by Campuzano‐Caballero and Uribe (, ) in Poecilia reticulata and Poeciliopsis gracilis .…”

“…These characteristics are a strategy allowing them to maximize fecundity, considering the small size of the body cavity which limits the number of eggs that can be spawned in each reproductive event. However, in many cyprinodontiforme species, the developing oocytes vary considerably in size (Uribe et al, ). Thus, this is a fundamental trait which allows annual killifishes to maximize the production of viable embryos in a small period of time that last flood periods in their extreme environments.…”

“…The origin of the cortical alveoli has been reported near the germinal vesicle (Selman, Wallace, & Barr, ; Tyler & Sumpter, ; Grier et al, ; Uribe et al, ), associated with regions of the Balbiani body (Domínguez‐Castanedo et al, ). Some organelles related to the synthesis of cortical alveoli are the same that conform the Balbiani body (endoplasmic reticulum, Golgi complex and mitochondria; Guraya, ; Bazzoli & Godinho, ; Quagio‐Grassiotto, Wildner, & Guimarӑes‐Bassoli, ); it is possible to suggest that the Balbiani body is involved in the synthesis of the cortical alveoli.…”