Wag Platy Medium Xiphophorus maculatus The southern platyfish, common platy or moonfish (Xiphophorus maculatus) is a species of freshwater fish in the family Poeciliidae of order Cyprinodontiformes. A live-bearer, it is closely related to the green swordtail (X. helleri) and can interbreed with it. It is native to an area of North and Central America stretching from Veracruz, Mexico, to northern Belize. The southern platyfish grows to a maximum overall length of 2.5 inches. Sexual dimorphism is slight, the male’s caudal fin being more pointed. The anal fin of the male fish has evolved into a gonopodium, a stick-shaped organ used for reproduction.