A spawning female‐specific substance reactive to anti‐chorion (egg envelope) glycoprotein antibody in the teleost, Oryzias latipes

A substance with high immunoreactivity to rabbit anti‐chorion (egg envelope) glycoprotein antibody was found in liver and blood plasma as well as ovary of the spawning female medaka, while it was absent in the male and the non‐spawning female fish. This substance disappeared first from the hepatic cells of the female fish when it ceased spawning, whereas the immunoreactivity still remained in ovary and blood plasma. The relative electrophoretic mobility of the antigenic substance derived from these tissues was identical. The molecular weight and isoelectric point (pI) of the substance, as determined by polyacrylamide electrophoresis with varied gel concentrations and isoelectric focusing method, were about 60,000 and about 4.5, respectively. The substance was evidently distinct from the unreactive band of probable vitellogenin (ca 420,000 and pI, ca 3.8–4.0) which was found in blood plasma of the spawning female. In ovary sections, cytoplasm of the oocyte at the initial stage of chorion formation, containing neither vitellogenin nor egg yolk, showed a strong immunoreactivity. Cytoplasm of the oocytes, later than the vitellogenic stage, exhibited little immunoreactivity. Changes of this substance in connection with the spawning cycle strongly suggest that this substance is related to oogenesis.