A unique family of membrane progestin receptors (mPRα, mPRβ, and mPRγ) that mediates rapid, nongenomic actions of progestins has been identified and characterized in several fish species as well as in Xenopus, sheep, rats, and humans. Most of the previous studies have focused on the functions and signalling of mPRα. In contrast, the physiological functions and signalling mechanisms of mPRβ have been poorly described. Previously, we expressed and characterized the receptor binding and rapid signalling of zebrafish mPRα and mPRβ in mammalian cell lines. In the present study, the expression of both mPRα and mPRβ in zebrafish oocytes and their functions were investigated.