Ophidion barbatum is an oviparous fish species, with external fertilization. In females, a single-lobed ovary is followed by a short oviduct that opens directly out through the genital opening. Ovarian development is asynchronous. In a mature ovary and during the breeding season, oocytes in various stages of development can be observed simultaneously. Six stages are described in the oogenesis from the oogonia to the mature egg, using different histological techniques and based on differences of staining, of size and on the nucleus and cytoplasm structure, as viewed through a light microscope. Three of them correspond to the previtellogenic phase and the other three to the vitellogenic phase. Atretic degeneration of eggs is also described. © 1993 Kluwer Academic Publishers.