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Splitfins, are a family, Goodeidae, of fish endemic to Mexico and some areas of the United States. This family contains 40 species within 18 genera^1][2]. The family is named after ichthyologist George Brown Goode.

Range and Geographic Distribution

The family is divided into two subfamilies, the Goodeinae and the Empetrichthyinae. The Goodeinae are endemic to shallow freshwater habitats in Mexico, particularly along the Mesa Central area, west of Mexico City, with some species found in brackish fringes at both the Atlantic and Pacific coasts. There are 36 species of Goodeinae in 16 genera. The Empetrichthyinae are typically found in the southwestern Great Basin of the United States, and contains 4 species in two genera.

Physical Information

The name "Splitfins" comes from the fact that, in the male fish, the anterior rays of the anal fin are partly separated from rest of the fin. Splitfins can be up to 20 cm in length, though most species are much smaller, around 5cm. Goodeid fish have internal fertilisation, with males positioning themselves with a flexible part of the front anal fin, separated by a notch, which makes up the andropodium. Embryos hatch out of the egg within the womb, and possess trophotaenia, a ribbon-like structure unique to Goodeids, positioned in front of the anal fin on the dorsal surface of the juvenile. These allow the absorption of nutrients within the womb (matrotrophy), and are shed by juveniles shortly after birth. Female Goode ids do not store sperm, and so a copulation event must precede each pregnancy^[3].

Conservation Status

In recent years there has been a significant reduction in the range and size of Goodeid populations in this region, mainly due to anthropogenic disturbances, such as pollution, eutrophication, habitat modification and desiccation; recent estimates put habitat loss at 80% compared to historic ranges ^[4]. The low economic importance of Goodeid fish to Mexican fisheries and industry has led to this family being largely ignored by conservation efforts, but their small size and the dedication of a small number of aquaria hobbyists has led to a recent increase in the amount of research dedicated to the family. These investigations have highlighted the implications for conservation efforts concerning other global freshwater ichthyofauna.

Several species are threatened or extinct according to the IUCN^[5] and the U.S. Fish and Wildlife Service^[6]:

• Vulnerable - Bold characodon, Darkedged splitfin, Goodea gracilis, Allotoca dugesii
• Endangered - Bluetail splitfin, Rainbow characodon, Relict splitfin, Tequila splitfin, Allotoca diazi, Manse Spring killifish
• Critically Endangered - Blackspot allotoca, Chapultepec splitfin, Highland splitfin, Balsas splitfin
• Extinct in the Wild - Butterfly splitfin, Golden skiffia
• Extinct - Ash Meadows killifish, Parras characodon, Raycraft poolfish, Pahrump Ranch poolfish

Life Cycle and Evolution

The majority of Goodeid fish are viviparous, typically giving birth to live young. The family includes a number of popular aquarium fish, for example the redtail splitfin Xenotoca eiseni. Recent phylogenetic studies have put the age of this family at approximately 16.5 million years, with the majority of divergence occurring in the Miocene period. The speciosity of this family can be attributed to historical volcanic and geological disturbance in this region, which created suitable conditions for allopatric speciation of the fish ^[2].

Species

There are 40 species in 18 genera:[1]

• Subfamily Empetrichthyinae
  • Genus Crenichthys
    • Crenichthys baileyi
      • Crenichthys baileyi albivallis Williams & Wilde, 1981.
      • White River springfish, Crenichthys baileyi baileyi Gilbert, 1893.
      • Crenichthys baileyi grandis Williams & Wilde, 1981.
      • Crenichthys baileyi moapae Williams & Wilde, 1981.
      • Crenichthys baileyi thermophilus Williams & Wilde, 1981.
    • Railroad Valley springfish, Crenichthys nevadae Hubbs, 1932.
  • Genus Empetrichthys
    • Empetrichthys latos Miller, 1948.
      • Raycraft poolfish, Empetrichthys latos concavus Miller, 1948.
      • Manse Spring killifish, Empetrichthys latos latos Miller, 1948.
      • Pahrump ranch poolfish, Empetrichthys latos pahrump Miller, 1948.
    • Ash Meadows killifish, Empetrichthys merriami Gilbert, 1893.
• Subfamily Goodeinae
  • Genus Allodontichthys
    • Whitepatched splitfin, Allodontichthys hubbsi Miller & Uyeno, 1980.
    • Finescale splitfin, Allodontichthys polylepis Rauchenberger, 1988.
    • Tuxpan splitfin, Allodontichthys tamazulae Turner, 1946.
    • Bandfin splitfin, Allodontichthys zonistius Hubbs, 1932.
  • Genus Alloophorus
    • Bulldog goodeid, Alloophorus robustus Bean, 1892.
  • Genus Allotoca
    • Catarina allotoca, Allotoca catarinae de Buen, 1942.
    • Patzcuaro allotoca, Allotoca diazi Meek, 1902.
    • Opal allotoca, Allotoca dugesii Bean, 1887.
    • Banded allotoca, Allotoca goslinei Smith & Miller, 1987.
    • Blackspot allotoca, Allotoca maculata Smith & Miller, 1980.
    • Zirahuen allotoca, Allotoca meeki Alvarez, 1959.
    • Allotoca regalis +++
    • Zacapu allotoca, Allotoca zacapuensis Meyer, Radda & Domínguez, 2001.
  • Genus Ameca
    • Butterfly splitfin, Ameca splendens Miller & Fitzsimons, 1971.
  • Genus Ataeniobius
    • Bluetail goodea, Ataeniobius toweri Meek, 1904.
  • Genus Chapalichthys
    • Barred splitfin, Chapalichthys encaustus Jordan & Snyder, 1899.
    • Polka-dot splitfin, Chapalichthys pardalis Alvarez, 1963.
    • Alien splitfin, Chapalichthys peraticus Alvarez, 1963.
  • Genus Characodon
    • Bold characodon, Characodon audax Smith & Miller, 1986.
    • Parras characodon, Characodon garmani Jordan & Evermann, 1898.
    • Rainbow characodon, Characodon lateralis Günther, 1866.
  • Genus Girardinichthys
    • Darkedged splitfin, Girardinichthys multiradiatus Meek, 1904.
    • Chapultepec splitfin, Girardinichthys viviparus Bustamante, 1837.
  • Genus Goodea
    • Blackfin goodea, Goodea atripinnis Jordan, 1880.
    • Goodea gracilis Hubbs & Turner, 1939.
  • Genus Hubbsina
    • Highland splitfin, Hubbsina turneri de Buen, 1940.
    • Girardinichthys ireneae Radda & Meyer, 2003.
  • Genus Ilyodon
    • Freckled splitfin, Ilyodon cortesae Paulo-Maya & Trujillo-Jiménez, 2000.
    • Goldbreast splitfin, Ilyodon furcidens Jordan & Gilbert, 1882.
    • Balsas splitfin, Ilyodon whitei-lennoni Meek, 1904.
    • Limones splitfin, Ilyodon xantusi Hubbs & Turner, 1939.
  • Genus Neoophorus
    • Balsas Goodeid, Neoophorus regalis Alvarez, 1959.
  • Genus Neotoca
    • Balsas Allotoca, Neotoca bilineata Bean, 1887.
  • Genus Skiffia
    • Twoline skiffia, Skiffia bilineata Bean, 1887.
    • Golden skiffia, Skiffia francesae Kingston, 1978.
    • Olive skiffia, Skiffia lermae Meek, 1902.
    • Spotted skiffia, Skiffia multipunctata Pellegrin, 1901.
  • Genus Xenoophorus
    • Relict splitfin, Xenoophorus captivus Hubbs, 1924.
  • Genus Xenotaenia
    • Leopard splitfin, Xenotaenia resolanae Turner, 1946.
  • Genus Xenotoca
    • Redtail splitfin, Xenotoca eiseni Rutter, 1896.
    • Black splitfin, Xenotoca melanosoma Fitzsimons, 1972.
    • Jeweled splitfin, Xenotoca variata Bean, 1887.
  • Genus Zoogoneticus
    • Picotee goodeid, Zoogoneticus quitzeoensis Bean, 1898.
    • Tequila splitfin, Zoogoneticus tequila Webb & Miller, 1998.