What is "xenotoca"

Xenotoca is a genus of fish within the goodeid family, Goodeidae. They belong to the subfamily Goodeinae. Like all members of this subfamily, they are livebearers. However, the goodeid method of mating is somewhat different from more common livebearers, such as guppies and swordtails. Rather than a gonopodium, goodeid males transmit sperm to the females using an andropodium, a notched anal fin which gives the fish the common name "splitfin".

All members of the genus Xenotoca live in the highlands of Mexico. While no goodeid is a very common aquarium fish, the Redtail Splitfin (X. eiseni), is one of the most common aquarium goodeids. Its bright colors - blue body and red tail - offset its reputation for nipping the fins of its tankmates.