抄録
The 4 morphological criteria for a new species of Japanese medaka, “Oryzias sakaizumii” proposed by Asai et al.（2011） were examined in males of 75 closed colonies derived from wild populations caught in the Japan islands and maintained for longer than 30 years in laboratory. Males of 14 colonies from the Northern population medaka （“O. sakaizumii” ） were identified only by one criterion: “dense network of melanophores along each scale margin on body side” , and it was impossible to distinguish the males of the Northern populations from those of the Southern population（O. latipes） by the other 3 criteria. In addition, it has been known that hybrid populations between the Southern and the Northern populations are present in Tajima-Tango area in wild, providing the evidence for crossing of the two medaka populations in Japan in this area. In this report, the author concludes that the Southern and the Northern populations of Japanese medaka are the same species and the Northern population is a geographical subspecies of O. latipes）, since both populations have crossed naturally and the confirmed morphological difference between them is slight, not giving a clear implication that these populations have differentiated into separate species.
