Xenotoca is a genus of fish within the goodeid family, Goodeidae

Goodeidae

Splitfins, are a family, Goodeidae, of teleost fish endemic to Mexico and some areas of the United States. This family contains 40 species within 18 genera. The family is named after ichthyologist George Brown Goode.-Range and Geographic Distribution:...

. They belong to the subfamily Goodeinae

Goodeinae

Goodeinae is a taxon of splitfins. It is a small fish which mostly lives in fresh water in Mexico, especially around Mesa Central, west of Mexico City. It is also found in brackish water on both the east and west coasts....

. Like all members of this subfamily, they are livebearers

Vivipary

Vivipary has two different meanings. In animals, it means development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs...

. 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

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

. While no goodeid is a very common aquarium fish, the Redtail Splitfin

Redtail splitfin

The Redtail Splitfin, or Redtail Goodeid, is a species of goodeid fish from the family Goodeidae and subfamily Goodeinae. Like other members of Goodeinae, the Redtail Splitfin is a livebearer. However, the goodeid mating system differs in several ways from the more common livebearing fish from...

 (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.

Species

The genus Xenotoca includes three described species:

• Xenotoca eiseni – Redtail Splitfin
  Redtail splitfin
  The Redtail Splitfin, or Redtail Goodeid, is a species of goodeid fish from the family Goodeidae and subfamily Goodeinae. Like other members of Goodeinae, the Redtail Splitfin is a livebearer. However, the goodeid mating system differs in several ways from the more common livebearing fish from...
  
  , Redtail Goodeid
• Xenotoca melanosoma Fitzsimons, 1972 – Black Splitfin
• Xenotoca variata (Bean
  Tarleton Hoffman Bean
  Tarleton Hoffman Bean was an American ichthyologist, born at Bainbridge, Pennsylvania on 8 October 1846. He died in Albany, New York on 28 December 1916.-FAMILY AND EDUCATION :...
  
  , 1887) – Jeweled Splitfin