In biology, gonochorism is a sexual system where there are two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric.
Gonochorism contrasts with simultaneous hermaphroditism but it may be hard to tell if a species is gonochoric or sequentially hermaphroditic e.g. parrotfish, Patella ferruginea. However, in gonochoric species individuals remain either male or female throughout their lives. Species that reproduce by thelytokous parthenogenesis and do not have males can still be classified as gonochoric.