Social familiarity, which is based on the ability to recognize familiar conspecific individuals following social association, influences mating receptivity in various vertebrates from fish to primates. We previously demonstrated that medaka (Oryzias Latipes) females recognize familiar males following prior visual exposure. Medaka females have high receptivity only to the familiar male. Here, we demonstrate that female receptivity is biphasically regulated by gonadotropin-releasing hormone 3-producing (GnRH3) neurons. GnRH3 neurons, comprising a central neuromodulatory system, receive multimodal sensory information and project their axons throughout the entire brain. To address the function of GnRH3 peptides, which are synthesized specifically in GnRH3 neurons, we searched gnrh3 mutant by targeting induced local lesions in genomes (TILLING) method and identified the gnrh3^S27P allele in which a conserved serine residue was changed to proline. Interestingly, the gnrh3^S27P/S27P females exhibited low female mating receptivity, irrespective of the visual exposure prior to mating. Our findings strongly suggest that the GnRH3 peptide is required for switching from low to high female receptivity. Furthermore, electrophysiologic analysis revealed that TN-GnRH3 neurons with a basal level of neural activity suppress female receptivity to any male (default mode). Visual exposure prior to mating facilitates TN-GnRH3 neuron activity (facilitated mode), which correlates with high female receptivity to the familiarized male. gnrh3^S27P/S27P females have a basal level of neural activity irrespective of the visual exposure, suggesting that GnRH3 peptides are required for the mode-switching of GnRH3 neurons via self-priming.