Goodeidae

Splitfins
Redtail splitfin, Xenotoca eiseni
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cyprinodontiformes
Family:	Goodeidae
Subfamilies
Empetrichthyinae Goodeinae See text for genera and species.

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

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 5 cm. 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 Goodeids do not store sperm, and so a copulation event must precede each pregnancy.

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. 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 and the U.S. Fish and Wildlife Service:

• 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.

Species

The Goodeidae contain around 45 living (and some recently extinct) species in about 20 genera and 2 subfamilies:

Subfamily Empetrichthyinae – springfishes and poolfishes

• Crenichthys – springfishes (2 species)
• Empetrichthys – poolfishes (1 living species, 1 recently extinct)
  • Empetrichthys latos Miller, 1948
    • Empetrichthys latos concavus – Raycraft Poolfish, Raycraft Ranch Killifish (extinct: mid-late 20th century)
  • Empetrichthys merriami – Ash Meadows Poolfish, Ash Meadows Killifish (extinct: early 1950s)

Subfamily Goodeinae – typical goodeids and splitfins

• Allodontichthys (4 species)
• Alloophorus – Bulldog Goodeid (monotypic)
• Allotoca – typical allotocas (8 species)
• Ameca – Butterfly Splitfin, Butterfly Goodeid (monotypic)
• Ataeniobius – Striped Goodeid, Bluetail Goodea (monotypic)
• Chapalichthys (2-3 species)
• Characodon – characodons (2 living species, 1 recently extinct)
• Girardinichthys (2 species)
• Goodea (2 species)
• Hubbsina (2 species, sometimes included in Girardinichthys)
• Ilyodon (3-5 species)
• Neoophorus – Balsas Goodeid (monotypic)
• Neotoca – Balsas Allotoca (monotypic)
• Skiffia – skiffias (4 species, one extinct in the wild)
• Xenoophorus – Relict Splitfin (monotypic)
• Xenotaenia – Leopard Splitfin (monotypic)
• Xenotoca (3 species)
• Zoogoneticus (2 species)