Embryonic stem (ES) cells are undifferentiated cell cultures that are derived from early developing animal embryos. ES cells retain the potential of differentiation into all cell types including germ cells and therefore provide a unique bridge linking in vitro and in vivo genetic manipulations. ES cells have been widely used in the production knockout mice. Attempts have been made to develop ES cells in fish. We used the medaka (Oryzias latipes) to develop the ES cell technology in a second vertebrate model. We have established feeder cell-free culture conditions and obtained several ES cell lines from midblastula embryos. These ES cells show all features of mouse ES cells including a diploid karyotype, the potential for differentiation into various cell types and chimera competence. This review is to use medaka ES cells to highlight the major advances and future prospects for obtaining and utilizing ES cells in model and aquaculture fish species.
