The redtail splitfin or redtail goodeid (''Xenotoca eiseni'') is a species of goodeid fish from the family

Goodeidae Goodeidae is a family of teleost fish endemic to Mexico and some areas of the United States. Many species are known as splitfins. This family contains about 50 species within 18 genera. The family is named after ichthyologist George Brown Goode ...

and subfamily

Goodeinae Goodeinae is a subfamily of splitfins from Mexico, part of the family Goodeidae. They are small fish which mostly live in fresh water, especially around Mesa Central, west of Mexico City. Members of the subfamily are also found in brackish water ...

. Like other members of Goodeinae, the redtail splitfin is native to Mexico and a livebearer. However, the goodeid mating system differs in several ways from the more common livebearing fish from the family

Poeciliidae The Poeciliidae are a family of freshwater fishes of the order Cyprinodontiformes, the tooth-carps, and include well-known live-bearing aquarium fish, such as the guppy, molly, platy, and swordtail. The original distribution of the family was t ...

that includes

guppies The guppy (), also known as millionfish and rainbow fish, is one of the world's most widely distributed tropical fish and one of the most popular freshwater aquarium fish species. It is a member of the family Poeciliidae and, like almost all ...

and

swordtail ''Xiphophorus'' is a genus of euryhaline and freshwater fishes in the family Poeciliidae of order Cyprinodontiformes, native to Mexico and northern Central America. The many ''Xiphophorus'' species are all known as platyfish (or platies) and s ...

s. While no goodeid species is a very popular aquarium fish, the redtail splitfin is one of the most popular. Only the male has the red-orange tail for which it is named. Its specific name honours the collector of the type, Gustav Eisen (1847–1940) who was Curator of Marine Invertebrates at the

California Academy of Sciences The California Academy of Sciences is a research institute and natural history museum in San Francisco, California, that is among the largest museums of natural history in the world, housing over 46 million specimens. The Academy began in 1853 ...

San Francisco, California San Francisco (; Spanish for " Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the fourth most populous in California and 17th ...

Range and habitat

The redtail splitfin comes from west-central

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

in the Grande de Santiago River basin and waters near

Compostela, Nayarit Compostela is the name of both a municipality and of a town in it that serves as the seat; both are in the Mexican state of Nayarit. The municipality had 62,925 (2005 census) in a total area of 1,848 km² (713.5 sq mi). The town and its mun ...

. It might also occur in the uppermost Ameca and

Armería River The Armería River is a river in western Mexico. It originates in central Jalisco, and flows southward through Jalisco and Colima to empty into the Pacific Ocean. See also *List of rivers of Mexico *List of rivers of the Americas by coastline ...

basins, but the taxonomic position of these populations remains unclear. Two additional populations, one from an

endorheic An endorheic basin (; also spelled endoreic basin or endorreic basin) is a drainage basin that normally retains water and allows no outflow to other external bodies of water, such as rivers or oceans, but drainage converges instead into lakes ...

basin in the

Etzatlán Etzatlán is a town and municipality, in Jalisco in central-western Mexico. The municipality covers an area of 306.27 km2. As of 2005, the municipality had a total population of 17,564. It is home to the world’s largest crochet canopy ...

region and another from the Coahuayana River, were formerly included in this species, but in 2016 they were described as '' X. doadrioi'' and '' X. lyonsi'' respectively. The redtail splitfin inhabits springs, pools, lakes, creeks and rivers, typically in places with little or no aquatic vegetation. It prefers shallow waters.

Description

The redtail splitfin is a deep-bodied fish, and males have a hump behind the head. The hump gets larger as the males get older. Adult males have a red-orange tail and tail-base. The upper part of the body and head are olive-brownish to dusky. A broad, poorly defined bluish-black band runs from the

gill cover The operculum is a series of bones found in bony fish and chimaeras that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding. Anatomy The opercular series contains four bon ...

to the tail, but it virtually disappears on the mid-body region. The throat and belly or yellowish to whitish. Females lack the red-orange and are overall more plainly colored. Females are generally slightly larger than males. Females grow to 7 centimeters (2.8 inches) while males grow to 6 centimeters (2.4 inches)

total length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish ...

. Among goodeids, the distinct red-orange tail and tail-base is unique to the males of the redtail splitfin and its close relatives ''X. doadrioi'' and ''X. lyonsi''.

Breeding

Male goodeids like the redtail splitfin have a notched anal fin that gives the fish the name "splitfin", instead of the

gonopodium Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

of poeciliids. This notched anal fin, or

andropodium Fins are distinctive anatomical features composed of bony spine (zoology), spines or Ray (fish fin anatomy), rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bon ...

, is used to transmit sperm to the female. The female nourishes the unborn young via trophotaeniae, which function like an

umbilical cord In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologi ...

in mammals. Females give birth about every 2 months to 10 to 50 fry. The newborn redtail splitfin fry are relatively large compared to most newborn livebearer fry, at about 15 millimeters (2/3 of an inch) long. In the wild, both male and female redtail splitfins prefer to mate with fish of similar size. This limits the sexual advantage to males that grow especially large. This minimizes the sexual dimorphism in the size of the fish between males and females.

Aquarium keeping

The redtail splitfin is not a very common aquarium fish, but it is one of the most common goodeids to be kept in the aquarium. They are not very demanding in the aquarium, although they prefer hard, alkaline water. They can tolerate a wide range of water temperatures, from 15 to 30 degrees Celsius (59 to 86 degrees Fahrenheit). They accept a wide range of foods, but do require some vegetable matter in their diets. Although they are generally peaceful, they are known to occasionally nip the fins of fellow aquarium residents. This behavior can be reduced by keeping the redtail splitfin in schools.

References

{{Taxonbar, from=Q806299 Goodeinae Freshwater fish of Mexico Endemic fish of Mexico Natural history of Jalisco Natural history of Nayarit Fish described in 1896 Taxa named by Cloudsley Louis Rutter Río Grande de Santiago