Oocyte-expressed fertilization factor that mediates sperm-egg binding and is essential for sperm entry into the egg (PubMed:30190407). Necessary and sufficient to mediate species-specific gamete recognition and fertilization, which is essential for vertebrate species performing external fertilization (PubMed:30190407). External fertilization cannot guarantee that only conspecific sperm reaches the egg by precopulatory mate choice: proteins such as Bouncer can therefore support the selection of conspecific sperm (PubMed:30190407). Expressed in oocytes (PubMed:30190407). Not expressed in testis (PubMed:30190407). Zebrafish oocytes expressing O.latipes protein Bouncer can be fertilized by O.latipes, but not zebrafish, sperm. Belongs to the SPACA4/bouncer family. Silent walls - Issue 210 of January 2019