Poecilia butleri

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Pacific molly
Poecilia butleri trio (cropped).jpg
A male (bottom left) with females
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cyprinodontiformes
Family: Poeciliidae
Genus: Poecilia
Species:
P. butleri
Binomial name
Poecilia butleri
Jordan, 1889

Poecilia butleri, the Pacific molly, is a species of poeciliid fish native to the estuaries, lagoons, bays, and slow flowing fresh waters of the Pacific slope of Mexico and El Salvador. It belongs to the shortfin molly species complex. Pacific mollies feed mainly on cyanobacteria and detritus.

Contents

Taxonomy and description

Poecilia butleri was originally described in 1889 by Jordan, who named it after his friend, the naturalist Amos Butler. [2] Rosen and Bailey reduced it to a synonym of P. sphenops . [3] Schultz and Miller disagreed and in 1971 restored P. butleri to species rank on the grounds of partial reproductive and geographic isolation. [4] P. butleri belongs to the Mollienesia subgenus [5] and P. sphenops (shortfin molly) species complex. The two species often occur together in nature. They easily hybridize in the laboratory to produce fertile offspring, but only one such hybrid has been recorded in the drainage of the Papagayo River, where the two mollies live together. This paucity points to reproductive barriers that have not yet been identified. [4]

Young Pacific mollies have faint dark bars, while adults are uniformly olive in color. [4] The fish inhabiting the Papagayo River drainage have four or five rows of orange spots on their flanks. [4] The caudal fin features few black spots, but they are numerous in the dorsal fin of both sexes. [2] The largest known specimen reached 93 mm in standard length. [6]

Distribution and habitat

P. butleri occurs along the Pacific drainage of Mexico and El Salvador, from the Fuerte River basin in Sonora southward to the mouth of the Comasagua River west of La Libertad, El Salvador; its true southern limit remains uncertain and it likely extends farther west in El Salvador. While it occurs in freshwater in northwestern Mexico, east of the Río Balsas it is primarily found in brackish and marine coastal habitats, and it is expected to inhabit many coastal lagoons of El Salvador. The species is abundant across much of its range. [6] Its range extends further north than that of P. sphenops. In the part of the range it shares with P. sphenops, P. butleri inhabits slower-flowing streams and is therefore more common near the coast. P. butleri and, on the Atlantic slope, P. mexicana , are the only shortfin molly species found in brackish lagoons and river mouths. [4]

Poecilia butleri is common in the upper reaches of the Ameca and Coahuayana rivers in Jalisco, where those populations appear to be introduced. [6] Its ovoviparity and preference for estuarine and freshwater habitats may facilitate its spread into Baja California, where it appears to have been accidentally introduced from Sinaloa in 1995 via containers for breeding Pacific white shrimp. The establishment of mollies in this area might affect native mullets, snappers, grunts, and snooks, which rely on salt marsh habitats for reproduction. [7]

Poecilia butleri occupies a wide range of coastal and inland shallow waters, including low-gradient streams, slow stretches of larger rivers, lagoons, estuaries, ocean bays and coastal pools, tolerating fresh to fully saline conditions. Water clarity ranges from clear to turbid or muddy, currents from still to moderate, and depths generally do not exceed 1 m. Substrates recorded include sand, silt, mud, gravel, rock and boulder, and the species occurs among diverse vegetation types—filamentous algae, Chara , Potamogeton , Eichhornia , Pistia , Typha , Juncus , Nasturtium , Salvinia —as well as in mangrove stands. [6] In the Papagayo River drainage, the Pacific molly occurs together with the characin Astyanax fasciatus , a Cichlasoma cichlid, and the goby Sicydium multipunctatum in slowly flowing waters over green algae-covered rocks and boulders; P. sphenops is also present in small numbers, apparently invading from the upper reaches. [4]

Ecology

Poecilia butleri is herbivorous and detrivorous; [5] [8] a gut analysis of specimens from the Quelite River and a mangrove swamp near Tecoman showed that the fish had fed exclusively on cyanobacteria. [5] It might also take dipterous larvae. [7] Its predators include the boat-billed heron. [9] The species may carry parasites such as trematodes, cestodes, and nematodes. [10]

Poecilia butleri reaches sexual maturity at five or six months. After a gestation of 28 days, the female gives birth to 20 to 60 young. [11] Reproductive season appears to be extended: juveniles 7.0–11 mm standard length have been collected from February through late July. [6]

References

  1. ↑ Maiz-Tome, L.; Daniels, A. (2019). "Poecilia butleri". IUCN Red List of Threatened Species . 2019 e.T191743A2002077. doi: 10.2305/IUCN.UK.2019-2.RLTS.T191743A2002077.en . Retrieved 30 November 2025.
  2. 1 2 Jordan, David Starr (1889). "List of fishes collected by Alphonse Forrer about Mazatlan, with descriptions of two new species, Heros beani and Poecilia butleri". Proceedings of the United States National Museum. 11: 330.
  3. ↑ Rosen, Donn E.; Bailey, Reeve M. (1963). "The poeciliid fishes (Cyprinodontiformes), their structure, zoogeography and systematics". Bulletin of the American Museum of Natural History. 126 (1): 49.
  4. 1 2 3 4 5 6 Schultz, R. Jack; Miller, Robert Rush (1971). "Species of the Poecilia sphenops Complex (Pisces: Poeciliidae) in México". Copeia. 1971 (2). American Society of Ichthyologists and Herpetologists (ASIH), Allen Press: 282–290. ISSN   0045-8511. JSTOR   1442828 . Retrieved 2025-11-26.
  5. 1 2 3 Sanchez, Jessica L.; Bracken-Grissom, Heather; Trexler, Joel C. (2019). "Freshwater-to-marine transitions may explain the evolution of herbivory in the subgenus Mollienesia (genus Poecilia, mollies and guppies)". Biological Journal of the Linnean Society. 27 (4): 753. Retrieved 20 August 2023.
  6. 1 2 3 4 5 Miller, Robert Rush (2005). Freshwater fishes of México. Chicago, Illinois, United States: University of Chicago Press. p. 232.
  7. 1 2 Palacios-Salgado, Diana S.; Ramirez-Valdez, Antonio; Ruiz-Campos, Guadalupe (2011). "First record and establishment of an exotic molly (Poecilia butleri) in Baja California Peninsula, Mexico". California Fish and Game. 97 (2): 98–103.
  8. ↑ Medina-Nava, Martina; Schmitter-Soto, Juan J.; Mercado-Silva, Norman; Rueda-Jasso, Rebeca A.; Ponce-Saavedra, Javier; Pérez-Munguía, Ricardo M. (2011). "Ecological guilds of fishes in streams of an arid subtropical drainage in western Mexico". Journal of Freshwater Ecology. 26 (4): 579–592.
  9. ↑ Biderman, John O.; Dickerman, Robert W. (1978). "Feeding Behavior and Food Habits of the Boat-billed Heron (Cochlearius cochlearius)". Biotropica. 10 (1). [Association for Tropical Biology and Conservation, Wiley]: 33–37. ISSN   0006-3606. JSTOR   2388102 . Retrieved 3 December 2025.
  10. ↑ Salgado-Maldonado, Gilberto (2006). "Checklist of helminth parasites of freshwater fishes from Mexico". Zootaxa. 1324: 1–357.
  11. ↑ Wischnath, Lawrence (1993). Atlas of livebearers of the world. Neptune City, New Jersey, USA: T. F. H. Publications.
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