Effect of 17β‐Estradiol on Growth of Oocytes in Cultured Ovarian Fragments of the Starfish, Asterina Pectinifera

The development of growing oocytes of the starfish, Asterina pectinifera, was divided into five stages according to their histological features. Specimens collected monthly from Rishiri Island throughout a year were used. The effect of 17 β‐estradiol on oocyte growth was investigated. When ovarian fragments taken from April females were cultured in artificial seawater containing Medium 199 and streptomycin sulfate for 3 days, oocytes within such fragments did not show any changes in diameter. However, when similar ovarian fragments were cultured in the presence of 10−5M 17 β‐estradiol, the oocyte diameters increased significantly. It is concluded that 17 β‐estradiol enhances the growth of starfish oocytes in cultured ovarian pieces.