Electron microscopy of the male phase of the ovotestis of Amphiprion ,frenafus, a protandric hermaphrodite, showed no connective tissue between male and female areas and, as the basal lamina was lacking both along the seminiferous tubules and round the previtellogenic oocytes, the male and female germ cells were only separated by their respective surrounding somatic cells (Sertoli and follicle cells). Besides previtellogenic oocytes, oocytes in meiotic prophase and very small (young) previtellogenic oocytes, were detected in the ovarian part, as spermatogenesis proceeded, revealing oogenetic activity. Degeneration of some previtellogenic oocytes and their follicle cells was discernible.
SynopsisHeterosexual gonad development in a sparid species, Lithognathus mormyrus, was studied by histological and cytological examination, during the first three years of life . Gonad bisexuality is achieved after two months of development, according to the cytological dynamics known in sparids . In one-year-old fishes, a variability in the gonad morphology of the juvenile ovotestis is shown : three different types of ovotestis have been identified within the same cohort : ovotestes with testicular prevalence (25%), testicular and ovarian equivalence (20%), and ovarian prevalence (55%) . This morphological variability of the juvenile ovotestes was consistent with the histocytological analysis of the sexual structure of the adult stock at the first sexual maturity, which constituted 55 .5% of functional males (stemming from the first two types of ovotestis) and 44.5 % of primary females (from the third type) . The plasticity of sexual expression in sparids is emphasized, revealing the potentialities of the ovotestis .
In Amphiprion frenatus, a protandric hermaphrodite, male sex inversion is characterized by a decrease of spermatogenic activity in the ovotestis followed by a degeneration of male gevm cells and an increase of oogenic activity. Among female germ cells, undifferentiated primordial germ cells (PGCs) were identified; their participation in building up the ovary is suggested. In addition, the unusual association of juveniles with a single adull member or juvenile groupings lacking the presence of a monogamous pair, induced in juveniles the anticipated sex differentiations (in either male or female orientation) in which not only spermatogonia and oogonia but also PGCs are involved.
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