The yellow swordtail (''Xiphophorus clemenciae'') is a species of freshwater

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

in 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 ...

. It is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the upper

Coatzacoalcos River The Coatzacoalcos is a large river that feeds mainly the south part of the state of Veracruz; it originates in the Sierra de Niltepec and crosses the state of Oaxaca in the region of the Isthmus of Tehuantepec, flowing for toward the Gulf of M ...

basin in southern

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 ...

. It is typically found in brooks and streams with slow current; it is less frequent in areas with strong current. The yellow swordtail is considered a

threatened Threatened species are any species (including animals, plants and fungi) which are vulnerable to endangerment in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of ''critical depensat ...

species by Mexican authorities. It reaches up to in

standard 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 m ...

. Unusually, the yellow swordtail appears to be the result of

hybrid speciation Hybrid speciation is a form of speciation where hybridization between two different species leads to a new species, reproductively isolated from the parent species. Previously, reproductive isolation between two species and their parents was th ...

, and its ancestors a platy species and a

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 ...

species. The southern mountain swordtail (''X. monticolus''), which is found further south in the Coatzacoalcos River basin than the yellow swordtail, is the result of a similar event. The fish is named in honor of Álvarez’ wife Clemencia, without whose help and advice made it possible for him to devote himself to the pursuit of his scientific research.

Sources

Xiphophorus Endemic fish of Mexico Freshwater fish of Mexico Taxa named by Jose Álvarez del Villar Fish described in 1959 Taxonomy articles created by Polbot {{Cyprinodontiformes-stub