The XX-XY sex-determination system in Oryzias luzonensis and O. mekongensis revealed by the sex ratio of the progeny of sex-reversed fish

Zoolog Sci. 2004 Oct;21(10):1015-8. doi: 10.2108/zsj.21.1015.


The sex-determining gene in Oryzias latipes and O. curvinotus has been proved to be DMY. Although O. curvinotus has the DMY gene on the Y chromosome which is homologous to the Y chromosome of O. latipes, the sex-determining mechanism of other Oryzias fishes has not been identified. In order to uncover the sex-determining mechanism of O. luzonensis and O. mekongensis, which are most closely related species to O. latipes and O. curvinotus, we analyzed the sex ratio of the progeny of sex-reversed fish. We were able to obtain sex-reversed males by the administration of methyltestosterone, and found that these yielded all-female offspring in both species. These results indicate that O. luzonensis and O. mekongensis have the XX-XY sex-determination system.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Estradiol / pharmacology
  • Gonads / anatomy & histology
  • Gonads / drug effects
  • Hermaphroditic Organisms*
  • Histological Techniques
  • Methyltestosterone / pharmacology
  • Oryzias / physiology*
  • Phylogeny
  • Sex Chromosomes / physiology*
  • Sex Determination Processes*
  • Sex Ratio*


  • Estradiol
  • Methyltestosterone