The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Poecilia mexicana
Poecilia mexicana
(Shortfin Molly)

Copyright Info
Poecilia mexicana Steindachner, 1863

Common name: Shortfin Molly

Synonyms and Other Names: (Mexican molly, Atlantic molly, orangefin molly).

Taxonomy: available through www.itis.govITIS logo

Identification: Distinguishing characteristics were given by Miller (1983) and Page and Burr (1991); the species is included in identification keys of Miller (1983) and Greenfield and Thomerson (1997). It is part of the P. sphenops complex. Photographs appeared in Bussing (1987), Dawes (1991), and Wischnath (1993).

Size: 11 cm.

Native Range: Atlantic Slope from Rio San Juan, Mexico, to Guatemala, possibly south to Nicaragua (Miller 1983; Page and Burr 1991).

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Poecilia mexicana are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
AZ196519902Lower Colorado Region; Lower Salt
CA196619761Salton Sea
CO196519862Alamosa-Trinchera; San Luis
FL201720181Tampa Bay
MT196919902Beaverhead; Ruby
NV196320196Havasu-Mohave Lakes; Lake Mead; Las Vegas Wash; Muddy; Upper Amargosa; White

Table last updated 7/25/2024

† Populations may not be currently present.

* HUCs are not listed for states where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Means of Introduction: Most introductions presumably were due to fish farm escapes or aquarium releases.

Status: Locally established in California (Swift et al. 1993), Colorado (Zuckerman and Behnke 1986), Idaho (Courtenay et al. 1988), and Nevada (Deacon and Williams 1984; Scoppottone et al. 1998). Reported from Arizona (Courtenay and Meffe 1989) and Texas (Howells 1992a); extirpated from Montana (Courtenay and Meffe 1989). It has become the most abundant fish species in Ash Springs, Nevada (Sigler and Sigler 1987).

Impact of Introduction: This species may prey upon native larval fishes (Scoppettone 1993). Species from the P. sphenops complex (specifically the Mexican molly) have negatively affected Moapa dace Moapa coriacea and White River springfish Crenichthys baileyi in Nevada (Lee et al. 1980 et seq.; U.S. Fish and Wildlife Service 1983). The Moapa dace is listed as federally endangered, and the Moapa White River springfish is being considered for listing (Scoppettone 1993; U.S. Fish and Wildlife Service 1994). Hoffman and Schubert (1984) reported that the parasitic copepod of the genus Pseudocaligus was transferred to Hawaii by way of P. mexicana.

Shortfin mollies, and other introduced poeciliids, have been implicated in the decline of native damselflies on Oahu, Hawaii. Often the distributions of the damselflies and introduced fishes were found to be mutually exclusive, probably resulting from predation of the fish on the insects (Englund 1999).

Remarks: There is considerable confusion surrounding U.S. records of this and other members of the P. sphenops complex. For instance, Howells (1992a) expressed doubt as to the authenticity of the report of this species in Texas because of the common difficulty in distinguishing it from other members of the species complex, as well as from various molly hybrids.  Maciolek (1984) and Devick (1991b) reported this species from Oahu, Hawaii; however, a recent report by Mundy (2005) indicates these fish are in fact a hybrid including both P. mexicana and P. sphenops (see account for Poecilia sp.).  There is a file report indicating that this species was collected in July 1984 in Kelly Warm Springs, Teton County, Wyoming; however, that record is apparently in error (Courtenay, personal communication). There is no mention of this species being found in Kelly Warm Springs by Courtenay et al. (1988) although another introduced poeciliid, P. reticulata, was reported from the site. Wischnath (1993) reported that natural hybrids with P. latipinna are known from the Rio Mante Canal in Mexico.

Voucher specimens: Colorado (MSB, uncataloged); Nevada (UF 91917).

References: (click for full references)

Bradley, W. G. and J. E. Deacon. 1967. The biotic communities of southern Nevada. Nevada State Museum Anthropological Papers No. 13, Part 4. 201-273.

Brown, C. J. D. 1971. Fishes of Montana. Montana State University, Bozeman, MT.

Bussing, W. A. 1987. Peces de las aguas continentales de Costa Rica. Editorial de la Universidad de Costa Rica, San Jose. 221 pp.

Courtenay, W. - Florida Atlantic University, Boca Raton, FL.

Courtenay, W. R., Jr., and J. E. Deacon. 1983. Fish introductions in the American southwest: a case history of Rogers Spring, Nevada. Southwestern Naturalist 28:221-224.

Courtenay, W. R., Jr., and G. K. Meffe. 1989. Small fishes in strange places: a review of introduced poeciliids. Pages 319-331 in G. K. Meffe, and F. F. Snelson, Jr., editors. Ecology and evolution of livebearing fishes (Poeciliidae). Prentice Hall, Englewood Cliffs, NJ.

Courtenay, W. R., Jr., D. A. Hensley, J. N. Taylor, and J. A. McCann. 1984. Distribution of exotic fishes in the continental United States. Pages 41-77 in W. R. Courtenay, Jr., and J. R. Stauffer, Jr., editors. Distribution, biology and management of exotic fishes. Johns Hopkins University Press, Baltimore, MD.

Courtenay, W. R., Jr., D. P. Jennings, and J. D. Williams. 1991. Appendix 2: exotic fishes. Pages 97-107 in Robins, C. R., R. M. Bailey, C. E. Bond, J. R. Brooker, E. A. Lachner, R. N. Lea, and W. B. Scott. Common and scientific names of fishes from the United States and Canada, 5th edition. American Fisheries Society Special Publication 20. American Fisheries Society, Bethesda, MD.

Cross, J. N. 1976. Status of the native fish fauna of the Moapa River (Clark County, Nevada). Transactions of the American Fisheries Society 105:503-508.

Deacon, J. E., and W. G. Bradley. 1972. Ecological distribution of fishes of Moapa (Muddy) River in Clark County, Nevada. Transactions of the American Fisheries Society 101(3):408-419.

Deacon, J. E., C. Hubbs, and B. J. Zahuranec. 1964. Some effects of introduced fishes on the native fish fauna of southern Nevada. Copeia 1964(2):384-388.

Devick, W. S. 1991b. Patterns of introductions of aquatic organisms to Hawaiian freshwater habitats. Pages 189-213 in new directions in research, management and conservation of Hawaiian freshwater stream ecosystems. Proceedings of the 1990 symposium on freshwater stream biology and fisheries management, Division of Aquatic Resources, Hawaii Department of Land and Natural Resources.

Englund, R.A. 1999. The impacts of introduced poeciliid fish and Odonata on the endemic Megalagrion (Odonata) damselflies of Oahu Island, Hawaii. Journal of Insect Conservation 3:225-243.

Hahn, D. E. 1966. An introduction of Poecilia mexicana (Osteichthyes: Poeciliidae) into Colorado. Southwestern Naturalist 11:296-312.

Hoffman, F.L., and G. Schubert. 1984. Some parasites of exotic fishes. Pages 233-261 in W.R. Courtenay, Jr., and J.R. Stauffer, Jr., (eds). Distribution, biology, and management of exotic fishes. The Johns Hopkins University Press, Baltimore, Maryland.

Holton, G. D. 1990. A field guide to Montana fishes. Montana Department of Fish, Wildlife and Parks, Helena, MT. 104 pp.

Howells, R. G. 1992a. Annotated list of introduced non-native fishes, mollusks, crustaceans and aquatic plants in Texas waters. Texas Parks and Wildlife Department, Management Data Series 78, Austin, TX. 19 pp.

Hubbs, C., and J. E. Deacon. 1964. Additional introductions of tropical fishes into southern Nevada. Southwest Naturalist 9:249-251.

Hubbs, C. L., W. I. Follett, and L. J. Dempster. 1979. List of the fishes of California. California Academy Science Occasional Papers 133. 51 pp.

Lee, D. S., C. R. Gilbert, C. H. Hocutt, R. E. Jenkins, D. E. McAllister, and J. R. Stauffer, Jr. 1980 et seq. Atlas of North American freshwater fishes. North Carolina State Museum of Natural History, Raleigh, NC.

Maciolek, J. A. 1984. Exotic fishes in Hawaii and other islands of Oceania. Pages 131-161 in W. R. Courtenay, Jr., and J. R. Stauffer, Jr., editors. Distribution, biology, and management of exotic fishes. The Johns Hopkins University Press, Baltimore, MD.

Mearns, A. J. 1975. Poeciliopsis gracilis (Heckel), a newly introduced poeciliid fish in California. California Fish and Game 61(4):251-253.

Miller, R. R. 1983. Checklist and key to the mollies of Mexico (Pisces: Poecilidae, Poecilia, subgenus Mollienesia) Copeia 1983(3):817-822.

Minckley, W. L. 1973. Fishes of Arizona. Arizona Fish and Game Department. Sims Printing Company, Inc., Phoenix, AZ.

Minckley, W. L., and J. E. Deacon. 1968. Southwestern fishes and the enigma of "endangered species." Science 159:1424-1432.

Moyle, P. B. 1976a. Inland fishes of California. University of California Press, Berkeley, CA.

Mundy, B. C.  2005.  Fishes of the Hawaiian Archipelago.  Bishop Museum Bulletins in Zoology, Number 6.

Page, L. M., and B. M. Burr. 1991. A field guide to freshwater fishes of North America north of Mexico. The Peterson Field Guide Series, volume 42. Houghton Mifflin Company, Boston, MA.

Scoppettone, G. G. 1993. Interactions between native and nonnative fishes of the upper Muddy River, Nevada. Transactions of the American Fisheries Society 122:599-608.

Scoppettone, G.G., P.H. Rissler, M.B. Nielsen, and J.E. Harvey. 1998. The status of Moapa coriacea and Gila seminuca and status information on other fishes of the Muddy River, Clark County, Nevada. Southwestern Naturalist 43:115-122.

Shapovalov, L., A. J. Cordone, and W. A. Dill. 1981. A list of freshwater and anadromous fishes of California. California Fish and Game 67(1):4-38.

Silvey, W. - Arizona Game & Fish.

St. Amant, J. A. 1966. Addition of Tilapia mossambica Peters to the California fauna. California Fish and Game 52:54-55.

Swift, C. C., T. R. Haglund, M. Ruiz, and R. N. Fisher. 1993. The status and distribution of the freshwater fishes of southern California. Bulletin of the Southern California Academy of Science 92(3):101-167.

U.S. Fish and Wildlife Service. 1983. The Moapa dace recovery plan. Prepared in cooperation with the Nevada Department of Wildlife. 32 pp.

U.S. Fish and Wildlife Service. 1994. Endangered and threatened wildlife and plants: animal candidate review for listing as endangered or threatened species. 50 CFR 17.11 & 17.12. Federal Register, November 15, 1994. 59(219):58982-589028. U.S. Department of the Interior, Washington, DC.

Woodling, J. 1985. Colorado's little fish: a guide to the minnows and other lesser known fishes in the state of Colorado. Colorado Division of Wildlife, Denver, CO. 77 pp.

Zuckerman, L. D., and R. J. Behnke. 1986. Introduced fishes in the San Luis Valley, Colorado. Pages 435-452 in R. H. Stroud, editor. Fish culture in fisheries management. Proceedings of a symposium on the role of fish culture in fisheries management at Lake Ozark, MO, March 31-April 3, 1985. American Fisheries Society, Bethesda, MD.

FishBase Summary

Author: Leo Nico, and Pamela J. Schofield

Revision Date: 4/15/2019

Peer Review Date: 9/6/2011

Citation Information:
Leo Nico, and Pamela J. Schofield, 2024, Poecilia mexicana Steindachner, 1863: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=861, Revision Date: 4/15/2019, Peer Review Date: 9/6/2011, Access Date: 7/25/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


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Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [7/25/2024].

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