- any of several small, brightly colored, viviparous, freshwater fishes of the genus Xiphophorus, native to Central America, having the lower part of the caudal fin elongated into a swordlike structure: often kept in aquariums.
- any of several small freshwater cyprinodont fishes of the genus Xiphophorus, esp X. helleri, of Central America, having a long swordlike tail
