Developmental Stages in the Wild Medaka, Oryzias latipes

Unfertilized eggs of wild type medaka, Oryzias latipes, were artificially inseminated and incubated at 26± 1℃. Careful observation of the process of embryonic development by light microscopy allowed division of the process into 39 stages based on the same diagnostic features of the developing embryos as in the orange-red type medaka（Zool. Sci. , 11: 825-839, 1994）. The principal diagnostic features are the number and size of blastomeres, form of the blastoderm, extent of epiboly, development of the central nervous system, number and form of somites, optic and otic development, development of the notochord, heart development, blood circulation, the size and movement of the body, development of the tail, membranous fin（fin fold）development, and development of such viscera as the liver, gall bladder, gut tube, spleen and swim（air）bladder. Wild medaka embryos exhibited the same diagnostic features as orange-red type embryos, except for the appearance and behavior of melanophores. After hatching, development of the larvae（fry）and young can be divided into five stages based on such diagnostic features as the fins, scales and secondary sexual characteristics. The developmental figures were made by modifying the original figures that were published by the present author in Zoological Science, vol.11, pp.825-839（1994）under the title of “Stages of normal development in the medaka Oryzias latipes”（copyright holder: The Zoological Society of Japan）.