Over the past few decades, Medaka (Oryzias latipes) has become a model animal in teleost species research due both to its short reproductive cycle and efficient proliferate capacity. Unfortunately, however, systematic data of its sexual differentiation and development have yet to be obtained. In the present study, we observed Medaka gonad development from the earliest recognizable stages through differentiation to maturation under a light microscope, after paraffin sectioning and hematoxylin-eosin staining. The results showed that among juveniles aged 5 to 10 days, the gonad located on the right side of the dorsal abdominal cavity and the germ cells was significantly larger than the surrounding somatic cells. Ten days after hatching, sexual differences between females and males became obvious, and germline cysts derived from oogonium division were present in the gonad. At 50 days after hatching, ovarian cavities and mature sperm were observed. Moreover, during the study we also observed the coexistence of two sexual characteristics during a male's development. Together, these observations fill current gaps in developmental and genetic biology that will allow a more efficient use of Medaka as an experimental model.
青鳉(Oryzias latipes)繁殖力强、繁殖周期短,为硬骨鱼类研究领域的模式生物。目前,尚无青鳉性腺分化与发育过程的系统资料。该文以青鳉孵化后不同时期的生殖腺为材料,经石蜡切片和HE染色后,于光学显微镜下观察其性腺的出现、分化及成熟过程。结果显示:孵化后5~10 d,仔鱼腹腔右侧已可见生殖腺,生殖细胞体积明显大于周围的体细胞;孵化后10 d,性腺开始分化,雌、雄性个体性腺出现结构上的差异,雌性个体内可明显观察到生殖包囊结构;随后,雌、雄性个体内先后可见卵子和精子的发生过程和组织学分期;孵化后50 d,首见卵巢腔结构和成熟精子。此外,还观察到性反转现象的特例,即两性特征共存的现象。该结果将为发育生物学、遗传生物学提供基础资料。
Keywords: Histological observation; Medaka; Paraffin sectioning; Sex reversal; Sexual differentiation and development.