timing of sexual differentiation in fish

H.Wada hwada at UTS2.S.U-TOKYO.AC.JP
Thu Dec 7 21:23:30 EST 1995


At  8:52 95.12.07 -0800, Chuck Miller wrote:
>I am posting this message for colleagues of mine. Replies can be directed
>to this news group or to me. The request is-----
>
>"We have been searching the literature for information regarding the timing
>of organ commitment to form ovary or testes in fish, but so far we haven't
>found much. Specifically , we are interested in this info. for the Japanese
>Medaka--but info. on any fish species will be useful." 

        I think it is a very interesting problem.  In the Medaka fish, a stable sex determination with male heterogamety (XY chromosomal) was demonstrated. Yamamoto showed that sex can be reversed by the oral administration of steroid hormones after hatching and he considered  the gonad of hatched fry was undifferentiated. But Satoh and Egami showed that primordial germ cells were distinguishable between sexes in 3 days after fertilization (before hatching). They described that in female embryos there were much numbers of germ cells and some of these were already in meiotic phase. Please check the refferences;

Yamamoto (1953)  J. exp. Zool. 123, 571-594
Yamamoto (1958)  J. exp. Zool. 137, 227-264
Yamamoto (1969) Sex differentiation. In Fish Physiology, vol.III, pp.117-175. Academic Press
Satoh and Egami (1972) J. Embryol. exp. Morph. 28, 385-395

Best wishes,

Hironori Wada
Zoological Institute, School of Science
University of Tokyo
e-mail: hwada at uts2.s.u-tokyo.ac.jp





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