Xiphophorus nigrensis, the Panuco swordtail, is a species of fish in the family Poeciliidae[2] that is endemic to a small part of the Pánuco River basin in Mexico.[1][3][4]
| Xiphophorus nigrensis | |
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| Male | |
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| Female | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Cyprinodontiformes |
| Family: | Poeciliidae |
| Genus: | Xiphophorus |
| Species: | X. nigrensis
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| Binomial name | |
| Xiphophorus nigrensis D. E. Rosen, 1960
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Taxonomy
editBeing a small swordtail, Xiphophorus nigrensis was originally considered a subspecies of X. pygmaeus.[5] Today it is recognized, along with X. multilineatus, as the closest related species to X. pygmaeus.[6] The three species form a clade within the larger clade of northern swordtails.[7] The similarity of the large males of X. nigrensis to the small males of X. cortezi, another northern swordtail, points to a close evolutionary relationship between these two species.[5]
Description
editThe body of Xiphophorus nigrensis is larger and deeper than that of X. pygmaeus. The males possess on their caudal fin a moderately to well-developed sword set off by a black line, from which the specific epithet nigrensis (niger meaning black and ensis sword in Latin) is derived. Pregnant females exhibit a dusky gravid spot on their bellies. Larger individuals are deeper-bodied and develop brilliant iridescent blue on their sides and flanks, which may somewhat conceal their midlateral black stripe.[5]
Populations regularly contain both large (up to 40 mm) and small adult males (down to 18 mm).[5] Large males possess swords, while small males do not. Small males are slender and of solid gold color.[7]
Distribution and habitat
editXiphophorus nigrensis is found in Rio Choy.[7] The species inhabits clear, deep, fast-flowing waters along undercut slopes of river and stream beds. The depth can be as great as 3 m (9.8 ft).[5]
Reproduction
editXiphophorus nigrensis readily hybridizes with X. pygmaeus; in fact, females of the latter species prefer X. nigrensis males to those of their own species because large X. nigrensis males court females while X. pygmaeus males merely sneak up and chase them instead. Small X. nigrensis males also exhibit sneak-chase behavior.[8]
References
edit- ^ a b Vega-Cendejas, M. (2019). "Xiphophorus nigrensis". IUCN Red List of Threatened Species. 2019: e.T191790A2003276. doi:10.2305/IUCN.UK.2019-2.RLTS.T191790A2003276.en. Retrieved 19 November 2021.
- ^ Froese, Rainer; Pauly, Daniel (eds.). "Xiphophorus nigrensis". FishBase. August 2019 version.
- ^ "Xiphophorus nigrensis". Retrieved 12 Sep 2012.
- ^ Kang, J.H.; M. Schartl; R.B. Walter; A. Meyer (2013). "Comprehensive phylogenetic analysis of all species of swordtails and platies (Pisces: Genus Xiphophorus) uncovers a hybrid origin of a swordtail fish, Xiphophorus monticolus, and demonstrates that the sexually selected sword originated in the ancestral lineage of the genus, but was lost again secondarily". BMC Evolutionary Biology. 13 (25): 25. Bibcode:2013BMCEE..13...25K. doi:10.1186/1471-2148-13-25. PMC 3585855. PMID 23360326.
- ^ a b c d e Donn Eric Rosen (1960). "Middle-American poeciliid fishes of the genus Xiphophorus". Bulletin of the Florida State Museum. Biological Sciences. 5 (4). University of Florida: 100–102, 187.
- ^ "Livebearers". Tropical Fish Hobbyist. Vol. 54, no. 5–8. 2006. p. 108.
- ^ a b c 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.
- ^ 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. Bibcode:1989BEcoS..24..341R. doi:10.1007/bf00293262. S2CID 20181010.