Xiphophorus pygmaeus

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Pygmy swordtail
Pygmy Swordtail.jpg
Yellow morph male pygmy swordtail
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cyprinodontiformes
Family: Poeciliidae
Genus: Xiphophorus
Species:
X. pygmaeus
Binomial name
Xiphophorus pygmaeus
(Hubbs & Gordon, 1943)

Xiphophorus pygmaeus, the pygmy swordtail, is a poeciliid fish from northeastern Mexico. It is the smallest of the swordtails. The male's sword is barely visible and the species is often called the swordless swordtail. It is sometimes kept in home aquaria, but is a rather delicate species.

Contents

Taxonomy and evolution

Xiphophorus pygmaeus is the smallest member of the genus Xiphophorus . [2] It is most closely related to X. multilineatus and X. nigrensis , and males in particular look similar to the small males of the latter two species. [3] The three species form a clade within the larger clade of northern swordtails. X. pygmaeus lost large-sized males and male traits associated with larger size: courtship behavior, body depth, and well-developed swords. Large size eventually reappeared in X. pygmaeus but the normally accompanying traits did not. [4]

Description

Females grow to 4.5 cm (1.8 in), while males attain 3.5 cm (1.4 in). The male's sword is only 1-2 mm long. [5] The species was originally thought to consist only of small-sized males (all less than 29 mm long and most less than 24 mm), but in 1994 it was discovered that two populations contain large males. [4]

The base color of the fish is gray-brown. [5] Both small and large males can be yellow, [4] but this color morph is very rare in nature because such flashy individuals are easy prey. No yellow females exist, and the trait appears to be sex-linked: male descendants of yellow males tend to be yellow too. [2] Males are generally more intensely colored than females. [6]

Distribution and habitat

Xiphophorus pygmaeus was discovered in Rio Axtla, a tributary of Río Pánuco, by Myron Gordon in 1939. At the type locality, the fish were found in swift water among a dense stand of a Vallisneria -like plant along a steep bank. X. montezumae and X. variatus are found in the same section of the river, but their preference for shallower and slower water isolated X. pygmaeus from them. [7]

Xiphophorus pygmaeus also inhabits Rio Axtla's tributaries Rio Tancuilin and Rio Huichihuayan. [3] Its preferred habitat is characterized by soft bottoms and large stands of submerged plants [3] such as Sagittaria . [8]

Reproduction

Male (up) and female (below) Xiphophorus pygmaeus.jpg
Male (up) and female (below)

Xiphophorus pygmaeus is unusual among swordtails in that females are not courted by males, [9] neither small nor large. [4] Instead, the males sneak up on females and chase them to enforce copulation. [9] In most Xiphophorus species, including the most closely related, X. nigrensis and X. multilineatus, large males court females, while small males rely on the "sneak-chase" strategy. X. pygmaeus females prefer to be courted, however, and thus choose males of X. nigrensis over males of their own species when they can. [9]

Xiphophorus pygmaeus breeds sparsely, with a female rarely giving birth to more than 10 fry at once. The fry are 6–7 mm (0.24–0.28 in) long at birth and usually not preyed upon by the adults. [2] [5]

In aquarium

Caring for X. pygmaeus in the home aquarium is challenging. The species requires excellent filtration and frequent water changes and does not do well in soft water or temperatures exceeding 24°C. The addition of fine-leaved aquatic plants such as Ceratophyllum demersum is recommended because the fish feed on such plants and algae as well as infusoria growing among them. [2]

Related Research Articles

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Livebearers are aquarium fish that retain the eggs inside the body and give birth to live, free-swimming young. Among aquarium fish, livebearers are nearly all members of the family Poeciliidae and include: guppies, mollies, platies and swordtails.

<span class="mw-page-title-main">Poeciliidae</span> Family of fishes

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 the Southeastern United States to north of Río de la Plata, Argentina, and Africa, including Madagascar. Due to release of aquarium specimens and the widespread use of species of the genera Poecilia and Gambusia for mosquito control, though, poeciliids can today be found in all tropical and subtropical areas of the world. In addition, Poecilia and Gambusia specimens have been identified in hot springs pools as far north as Banff, Alberta.

<span class="mw-page-title-main">Southern platyfish</span> Species of fish

The southern platyfish, common platy, or moonfish is a species of freshwater fish in family Poeciliidae of order Cyprinodontiformes. A live-bearer, it is closely related to the green swordtail and can interbreed with it. It is native to an area of North and Central America stretching from Veracruz, Mexico, to northern Belize.

<i>Xiphophorus</i> Genus of fishes

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 and swordtails. Platyfish formerly were classified in another genus, Platypoecilia, which is now obsolete. The type species is X. hellerii, the green swordtail. Like most other new world Poeciliids, platies and swordtails are live-bearers that use internal fertilization and give birth to live young instead of laying eggs like the bulk of the world's fishes. The name Xiphophorus derives from the Greek words ξίφος (dagger) and φόρος (bearer), referring to the gonopodium on the males. All are relatively small fishes, which reach a maximum length of 3.5–16 cm (1.4–6.3 in) depending on the exact species involved.

<span class="mw-page-title-main">Monterrey platyfish</span> Species of fish

The Monterrey platyfish is a species of freshwater fish in family Poecilidae. A live-bearer, it was native to a very small section of the San Juan River system in the vicinity of the city of Monterrey, Mexico. The specific name refers to the American soldier and naturalist Darius N. Couch (1822–1897) who collected the type on a self financed expedition to Mexico.

<i>Poecilia wingei</i> Species of fish

Poecilia wingei, known to aquarists as Endlers or Endler's livebearer, in the genus Poecilia, is a small fish native to the Paria Peninsula in Venezuela. They are prolific breeders and often hybridize with guppies. These very colorful hybrids are the easiest to find being offered in pet-shops, typically under the name Endler's guppy.

The northern platyfish is a small, endangered species of fish in the family Poeciliidae. It is endemic to the vicinity of Cuatro Ciénegas in the Mexican state of Coahuila. It is restricted to hot-spring heated ditches and marshes of the Laguna Santa Tecla. Its native water is shallow and vegetation-choked, with very stable temperatures that generally are around 27–30 °C (81–86 °F), although captive studies show the species also can live in slightly colder water.

The Chiapas swordtail or upland swordtail is a species of livebearing freshwater fish of family Poeciliidae, and genus Xiphophorus. It is, therefore, in the same genus as the common platy and the swordtail. The Chiapas swordtail was discovered and first described by Donn E. Rosen in 1960, along with four other species of Xiphophorus.

<i>Heterandria formosa</i> Species of fish

Heterandria formosa is a species of livebearing fish within the family Poeciliidae. This is the same family that includes familiar aquarium fishes such as guppies and mollies. Heterandria formosa is not as commonly kept in aquaria as these species. Despite the common name "least killifish", it belongs to the family Poeciliidae and not to one of the killifish families. H. formosa is one of the smallest fish species; the 1991 Baensch Aquarium Atlas listed it as the 7th smallest fish in the world, and as of 2006 it remains the smallest fish species found in North America.

<span class="mw-page-title-main">Green swordtail</span> Species of fish

The green swordtail is a species of freshwater/brackish fish in family Poeciliidae of order Cyprinodontiformes. A live-bearer, it is closely related to the southern platyfish or 'platy' and can crossbreed with it. It is native to an area of North and Central America stretching from Veracruz, Mexico, to northwestern Honduras.

<i>Neoheterandria elegans</i> Species of fish

Neoheterandria elegans or Tiger Teddy is a small live-bearing fish within the family Poeciliidae. This is the same family that includes familiar aquarium fishes such as guppies and swordtails, although Neoheterandria elegans is not nearly as popular as an aquarium fish. The fish is found in the Truando River in Colombia. Males grow to 2.0 centimetres (0.79 in) and females grow to 2.5 centimetres (0.98 in). The front half of the fish is mostly silver but the rear has alternating gold and black vertical bars.

Xiphophorus nigrensis, the Panuco swordtail, is a species of fish in the family Poeciliidae that is endemic to a small part of the Pánuco River basin in Mexico.

Xiphophorus multilineatus is a fish in the family Poeciliidae. It is endemic to a small part of the Pánuco River basin in Mexican.

<i>Xiphophorus montezumae</i> Species of fish

Xiphophorus montezumae, the Montezuma swordtail, is a livebearing freshwater fish of the order Cyprinodontiformes, family Poeciliidae, and genus Xiphophorus. It is in the same genus as the common platy and the swordtail. Xiphophorus means 'sword-tail' in Greek.

<i>Xiphophorus continens</i> Species of fish

Xiphophorus continens, also known as El Quince swordtail or short-sword platyfish, is a live-bearing freshwater fish in the family Poeciliidae. It is endemic to the Pánuco River basin in east-central Mexico. Its name comes from the Greek conto, meaning short, and Latin ensis, meaning "sword". due to the species' sword size in males.

Xiphophorus malinche, also known as highland swordtail, is a live bearing fish in the family Poeciliidae. It is endemic to the Pánuco River basin in east-central Mexico. This species is named after La Malinche, an Indian slave who played a role in the Spanish conquest as the interpreter, secretary, and mistress of Hernando Cortes.

<span class="mw-page-title-main">Poeciliinae</span> Subfamily of fishes

Poeciliinae is a subfamily of killifish from the family Poeciliidae which contains species from the Americas which are collectively known as the livebearers because many, but not all, of the species within the subfamily are ovoviviparous.

<i>Alfaro cultratus</i> Species of fish

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<i>Limia melanogaster</i>

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<i>Xiphophorus milleri</i> Species of fish

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References

  1. ↑ Daniels, A.; Maiz-Tome, L. & Lyons, T.J. (2019). "Xiphophorus pygmaeus". IUCN Red List of Threatened Species . 2019: e.T191791A2003283. doi: 10.2305/IUCN.UK.2019-2.RLTS.T191791A2003283.en . Retrieved 24 April 2023.
  2. 1 2 3 4 Lothar Wischnath (1989). "Livebearers". Tropical Fish Hobbyist. Vol. 38, no. 1–4. p. 17-18.
  3. 1 2 3 "Livebearers". Tropical Fish Hobbyist. Vol. 54, no. 5–8. 2006. p. 108.
  4. 1 2 3 4 Molly R. Morris; Michael J. Ryan (April 1995). "Large body size in the pygmy swordtail Xiphophorus pygmaeus". Biological Journal of the Linnean Society. 54 (4): 383–395. doi:10.1111/j.1095-8312.1995.tb01044.x.
  5. 1 2 3 Herbert R. Axelrod; Lothar Wischnath (1991). Swordtails and Platies. TFH Publications. p. 32. ISBN   0866220909.
  6. ↑ Gary K. Meffe; Franklin F. Snelson (1989). Ecology and Evolution of Livebearing Fishes (Poeciliidae). Prentice Hall. pp. 105, 182. ISBN   9780132227209.
  7. ↑ Myron Gordon (26 August 1953). "The Ecological Niche of the Pygmy Swordtail, Xiphophorus pygmaeus, in the Río Axtla, Mexico". Copeia . 1953 (3): 148–150. doi:10.2307/1439920. JSTOR   1439920 . Retrieved 14 April 2023.
  8. ↑ Donn Eric Rosen (1960). "Middle-American Poeciliid Fishes of the Genus Xiphophorus". Bulletin of the Florida State Museum: Biological Sciences. University of Florida. 5 (4): 159.
  9. 1 2 3 M. J. Ryan; B. A. Causey (1989). ""Alternative" Mating Behavior in the Swordtails Xiphophorus nigrensis and Xiphophorus pygmaeus (Pisces: Poeciliidae)". Behavioral Ecology and Sociobiology. 24 (6): 341–348. doi:10.1007/BF00293262. S2CID   20181010.
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