Transgenic medaka enables easy oocytes detection in live fish.

Easy oocyte detection in living specimens benefits various developmental biology and environmental toxicology studies. One of the earliest markers of sex differentiation in medaka (Oryzias latipes) is oocyte development. Within the field of toxicology, a simple detection method for induced oocyte in the testis (testis-ova) as a result of endocrine disruption is necessary.