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Molly
Male molly
Conservation status
Least Concern  (IUCN 3.1)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cyprinodontiformes
Family:	Poeciliidae
Genus:	Poecilia
Species:	P. sphenops
Binomial name
Poecilia sphenops (Valenciennes, 1846)
Synonyms
Synonymy Mollienisia sphenops (Valenciennes, 1846) Poecilia thermalis Steindachner, 1863 Gambusia modesta Troschel, 1865 Gambusia plumbea Troschel, 1865 Poecilia chisoyensis Günther, 1866 Poecilia dovii Günther, 1866 Poecilia spilurus Günther, 1866 Platypoecilus mentalis Gill, 1877 Poecilia boucardii Steindachner, 1878 Platypoecilus nelsoni Meek, 1904 Platypoecilus tropicus Meek, 1907 Poecilia tenuis Meek, 1907 Poecilia spilonota Regan, 1908 Poecilia caudata Meek, 1909 Mollienesia macrura Hubbs, 1935 Mollienesia vantynei Hubbs, 1935 Mollienesia altissima Hubbs, 1936 Mollienesia pallida de Buen, 1943 Lembesseia parvianalis Fowler, 1949

Poecilia sphenops, called the Mexican molly or simply the molly, is a species of poeciliid fish from Central America. It was once understood as a widespread species with numerous local variants ranging from Mexico to Venezuela, but these variants are today considered distinct species belonging to the P. sphenops complex and P. sphenops itself as being native to Mexico, Guatemala, and Honduras. Due in part to its popularity as an aquarium fish, the species has been introduced outside of its native range, but many records may in fact refer to P. mexicana or other species from the complex. P. sphenops has been crossbred with other mollies, notably P. latipinna and P. velifera, to produce fancy mollies for the ornamental fish trade.

Taxonomy

P. sphenops is placed in the subgenus Mollienesia (mollies) according to the prevailing taxonomic classification of species within the genus Poecilia, and more precisely within the shortfin molly clade, so named because they have a shorter dorsal fin than the sailfin mollies.

All shortfin mollies were once considered local variants of a highly polytypic P. sphenops species distributed from the Río Grande basin in north-eastern Mexico to the coast of Venezuela, but currently prevailing view is that the shortfin mollies constitute the P. sphenops species complex of around 13 distinct species. The P. sphenops complex is sometimes further divided into a P. sphenops complex comprising species from the Atlantic slope and a P. mexicana complex from the Pacific slope. P. sphenops is frequently confused with P. mexicana; the two species, as well as the respective complexes, differ in the shape of their inner jaw teeth, which are tricuspid in P. sphenops and unicuspid in P. mexicana.

Description

P. sphenops can grow to 8.4 cm (3.3 in) standard length or 10 cm (3.9 in) total length, but is usually smaller. The species is dimorphic, with females growing around 1 cm (0.39 in) larger than males. Males, which are the more intensely colored sex, grow little or not at all after their gonopodium fully develops.

Distribution and habitat

P. sphenops occurs in both the Atlantic and Pacific slope of Mexico and the northern parts of Central America. On the Atlantic side it ranges from the Palma Sola River in the north to the basin of the Coatzacoalcos River and the headwaters of the Grijalva River in the south. On the Pacific slope it is distributed from the middle of the Río Verde basin in the state of Oaxaca to western Honduras and northern Guatemala. P. sphenops frequently occurs together with P. mexicana, but in short coastal streams the former tends to occupy upstream and the latter downstream habitats.

P. sphenops has been introduced outside of its native range through escapes and intentional releases by aquarists and fish farms. It is considered naturalized in the US states of Montana and Nevada as well as in Puerto Rico and reported from California and Arizona, but some or all of these populations may turn out to represent another species of the P. sphenops complex. Conversely, introductions attributed to P. mexicana may represent P. sphenops. Once established in an area, the species tends to disperse and colonize new sites without human intervention.

P. sphenops inhabits freshwater and brackish habitats, with typical habitats including rivers, ponds, lagoons, roadside ditches, and creeks. It is particularly widespread in creeks, and may be found in both lowlands and uplands. It occurs in stagnant water as well as in waters with slight and moderate flow. Such waters may be clear, turbid, or muddy, and are typically not deeper than 1 m (3 ft 3 in). The habitats may feature substrates of marl, clay, silt, mud (which is often deep), rock or bedrock. Some of the habitats are devoid of vegetation, while in others algae (e.g. Chara) and plants such as Lemna, Nasturtium, fine-leaved Potamogeton, Sagittaria, and Typha species are abundant. P. sphenops survives in temperatures ranging from 10.8–11.8°C to 38.8–39.5°C when acclimated in a range of 20–35°C.

Diet

P. sphenops is highly adaptable in terms of diet, utlizing a variety of food sources in different habitats. Algae and diatoms form a significant part of the diet. Different populations of the species have been recorded browsing on filamentous algae, filtering phytoplankton, rotifers, and crustaceans, preying on protozoa and insect larvae, or feeding chiefly on detritus. Because of their larger size, females can feed on a wider array of prey than males. In the aquarium the species browses on green algae and readily accepts dried food.

Reproduction

P. sphenops is a livebearer, producing up to 150 young after a month-long gestation. Young fish have been captured from January to August, indicating that the species reproduces throughout much of the year. In rivers the adults congregate close to the banks, while the fry stay in very shallow water. As with other members of its species complex, P. sphenops does not exhibit courtship display; instead, males sneak up to females and force copulation.

Males do not live long after reaching sexual maturity. As in other poeciliids, populations tend to contain more females than males. Males are more susceptible to stress and metabolic aging, less resistant to adverse environmental conditions, and predated on more easily due to their smaller size and more conspicuous colors.

Commercial value

Fish marketed as Poecilia sphenops are among the most popular subjects in ornamental fish trade worldwide. The black molly is commonly defined in aquarium literature as a black breeding form of P. sphenops, but black mollies comprise fish with different pedigrees. Ichthyologist Eugene K. Balon attributed the origin of the black molly to the crossbreeding of P. sphenops with the sailfin P. latipinna. The exact origin of the fancy mollies remains disputed.

The commercial value of Poecilia sphenops in the fisheries of Mexico is very low. The fish are exploited in artesian fisheries for human consumption in parts of the state of Oaxaca, and are suitable for aquaculture because of their thermal adaptability.

References

1. Matamoros, W.A. (2019). "Poecilia sphenops". IUCN Red List of Threatened Species. 2019: e.T191753A2002434. doi:10.2305/IUCN.UK.2019-2.RLTS.T191753A2002434.en. Retrieved 19 November 2021.
2. Froese, Rainer; Pauly, Daniel (eds.). "Poecilia sphenops". FishBase. June 2024 version.
3. ^ Alda, Fernando; Reina, Ruth G.; Doadrio, Ignacio; Bermingham, Eldredge (2013). "Phylogeny and biogeography of the Poecilia sphenops species complex (Actinopterygii, Poeciliidae) in Central America". Molecular Phylogenetics and Evolution. 66 (3): 1011–1026. doi:10.1016/j.ympev.2012.12.012.
4. ^ Gómez-Márquez, José L.; Peña-Mendoza, Bertha; Guzmán-Santiago, José L. (2016). "Reproductive biology of Poecilia sphenops Valenciennes, 1846 (Cyprinidontiformes: Poeciliidae) at the Emiliano Zapata Reservoir in Morelos, Mexico" (PDF). Neotropical Ichthyology. 14 (2). doi:10.1590/1982-0224-20140127. ISSN 1679-6225. Retrieved 7 January 2025.
5. ^ Miller, R.R.; Minckley, W.L.; Norris, S.M. (2005). Freshwater Fishes of México. University of Chicago Press. pp. 238–239. ISBN 978-0-226-52604-1. Retrieved 2025-01-07.
6. ^ Nico, Leo; Schofield, Pamela J.; Neilson, Matt; Loftus, Bill (24 October 2016). "Mexican Molly (Poecilia sphenops)". USGS Nonindigenous Aquatic Species Database. Retrieved 7 January 2025.
7. ^ Palacios, Maura; Voelker, Gary; Arias Rodriguez, Lenin; Mateos, Mariana; Tobler, Michael (2016). "Phylogenetic analyses of the subgenus Mollienesia (Poecilia, Poeciliidae, Teleostei) reveal taxonomic inconsistencies, cryptic biodiversity, and spatio-temporal aspects of diversification in Middle America". Molecular Phylogenetics and Evolution. 103: 230–244. doi:10.1016/j.ympev.2016.07.025. Retrieved 2025-01-07.
8. Bagley, Justin C.; Alda, Fernando; Breitman, M. Florencia; Bermingham, Eldredge; van den Berghe, Eric P.; Johnson, Jerald B. (2015-04-07). "Assessing Species Boundaries Using Multilocus Species Delimitation in a Morphologically Conserved Group of Neotropical Freshwater Fishes, the Poecilia sphenops Species Complex (Poeciliidae)". PLOS ONE. 10 (4): e0121139. doi:10.1371/journal.pone.0121139. ISSN 1932-6203. PMC 4388586. PMID 25849959.
9. Dill, W.A.; Cordone, A.J. (1997). "History and status of introduced fishes in California, 1871-1996" (PDF). Fish Bulletin. California Department of Fish and Game. Retrieved 7 January 2025.
10. Lee, David S.; Gilbert, Carter R.; Hocutt, Charles H.; Jenkins, Robert E.; McAllister, Don E.; Stauffer Jr., Jay R. (1980). Atlas of North American Freshwater Fishes. North Carolina State Museum of Natural History. p. 651. ISBN 0917134036.
11. Hernández-Rodríguez, Mónica; Bückle-Ramirez, L. Fernando (2010). "Preference, tolerance and resistance responses of Poecilia sphenops Valenciennes, 1846 (Pisces: Poeciliidae) to thermal fluctuations". Latin American Journal of Aquatic Research. 38 (3): 427–437. doi:10.3856/vol38-issue3-fulltext-7. ISSN 0718-560X.
12. ^ Trujillo-Jiménez, Patricia; Beto, Héctor Toledo (1 July 2007). "(PDF) Diet of the tropical freshwater fish Heterandria bimaculata (Haeckel) and Poecilia sphenops Valenciennes (Cyprinidontiformes: Poeciliidae)". Revista de Biologia Tropical. 55 (2). Universidad de Costa Rica: 603–15. ISSN 0034-7744. PMID 19069770. Retrieved 7 January 2025.
13. Riehl, R.; Baensch, H.A. (1991). Aquarien Atlas (in German). Vol. 1. Melle: Mergus, Verlag für Natur-und Heimtierkunde. p. 992.
14. Wischnath, L. (1993). Atlas of livebearers of the world. T.F.H. Publications, Inc. p. 336.
15. Warren, M.L.; Burr, B.M.; Tomelleri, J.R.; Echelle, A.A.; Kuhajda, B.R.; Ross, S.T. (2020). Freshwater Fishes of North America: Volume 2: Characidae to Poeciliidae. Johns Hopkins University Press. p. 726. ISBN 978-1-4214-3512-1. Retrieved 9 January 2025.
16. ^ Schäfer, Frank (19 August 2022). "Wer kennt das Volk der Mollienser?". aqualog.de (in German). Retrieved 8 January 2025.
17. Balon, Eugene K. (1 April 2006). "The oldest domesticated fishes, and the consequences of an epigenetic dichotomy in fish culture". Aqua: Journal of Ichthyology & Aquatic Biology. 11 (2). Aquapress Publisher: 47–87. ISSN 0945-9871. Retrieved 7 January 2025.
18. Hernández, M; Bückle, L F; Espina, S (13 September 2002). "Temperature preference and acclimation in Poecilia sphenops (Pisces, Poeciliidae)". Aquaculture Research. 33 (12). Wiley: 933–940. doi:10.1046/j.1365-2109.2002.00744.x. ISSN 1365-2109. Retrieved 8 January 2025.
19. Hernández-Rodríguez, Mónica; Bückle-Ramirez, L. Fernando (1 January 2010). "(PDF) Preference, tolerance and resistance responses of Poecilia sphenops Valenciennes, 1846 (Pisces: Poeciliidae) to thermal fluctuations". Latin American Journal of Aquatic Research. 38 (3). Pontificia Universidad Catolica de Valparaiso. doi:10.3856/vol38-issue3-fulltext-7. ISSN 0718-560X. Retrieved 8 January 2025.

• IUCN Red List least concern species
• Poecilia
• Freshwater fish of Mexico
• Fish of Guatemala
• Fish of Honduras
• Fish described in 1846
• Taxa named by Achille Valenciennes