Xenotoca is a genus of livebearing splitfins in family Goodeidae, endemic to central Mexico. Like other goodeids, they are viviparous, giving birth to free-swimming young nourished in the womb through a placenta-like structure rather than a yolk sac, and most species are confined to small, isolated springs, streams, and lakes on the Mexican highland plateau.
The redtail splitfin (Xenotoca eiseni) is the genus's best-known aquarium species, long kept for its peaceful schooling behavior and the males' vivid orange-red tail band, and it remains a mainstay of the livebearer and goodeid-keeping hobby. The rest of the genus - the San Marcos redtail splitfin (X. doadrioi), Tamazula redtail splitfin (X. lyonsi), black splitfin (X. melanosoma), and jeweled splitfin (X. variata) - is far more range-restricted and far more threatened: the atlas tallies two Critically Endangered and two Endangered species against a single Least Concern one, with four species flagged for CARES conservation priority. That pattern reflects a broader goodeid decline across the Mexican highlands, driven by spring depletion, introduced predatory fish, and habitat loss.