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 formosa
Poecilia formosa
(Amazon Molly)
Native Transplant

Copyright Info
Poecilia formosa (Girard, 1859)

Common name: Amazon Molly

Taxonomy: available through www.itis.govITIS logo

Identification: Distinguishing characteristics were given in Miller (1983), Hubbs et al. (1991), and Page and Burr (1991); other names used in the past for this species include Mollienesia formosa and Limia formosa (Hubbs 1955; Miller 1983). It was included in Miller's (1983) key to the Mexican Poecilia. A photograph appeared in Dawes (1991).

Size: 9.6 cm.

Native Range: Rio Grande drainage, extreme southern Texas; also in Mexico south to Veracruz (Miller 1983; Page and Burr 1991).

Native range data for this species provided in part by NatureServe NS logo
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 formosa are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
TX1953201713Aransas; Lavaca; Lower Brazos; Lower Guadalupe; Lower Nueces; Lower San Antonio; Medina; Middle Guadalupe; Mission; San Marcos; South Corpus Christi Bay; Upper San Antonio; West Matagorda Bay

Table last updated 6/15/2024

† Populations may not be currently present.

Ecology: Prefers sluggish streams and ditches. Found sympatrically with P. latipinna and P. mexicana, Amazon mollies are thought to be a hybrid of these two species (see Remarks).

Means of Introduction: Unknown.

Status: Several introduced populations have been documented in Texas (e.g, Hubbs et al. 1991; Page and Burr 1991); as such, it can be assumed that the species is, at a minimum, locally established.

Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

Remarks: Poecilia formosa is a gynogenetic, unisexual (all-female) molly of hybrid origin between sailfin (P. latipinna) and shortfin (P. mexicana) mollies (Hubbs 1955; Miller 1983). The spermatozoa from a related species stimulate egg development but do not contribute any genetic material (Meffe and Snelson 1989). There is some doubt concerning the positive identification of this and some of the other molly species taken in Texas and as to whether certain populations are actually nonnative or possibly hybrids (Howells 1992a).

References: (click for full references)

Conner, J. V., and R. D. Suttkus. Zoogeography of freshwater fishes of the western Gulf slope of North America. 413-456 in C.H. Hocutt and E.O. Wiley, eds. The zoogeography of North American freshwater fishes. John Wiley and Sons, New York, NY.

Dawes, J. A. 1991. Livebearing Fishes. A Guide to Their Aquarium Care, Biology and Classification. Blandforn, London, England.

Drewry, G. E., E. A. Delco Jr., and C. Hubbs. 1958. Occurrence of the Amazon Molly, Mollienesia formosa, at San Marcos, Texas. Texas Journal of Science 5(4):489-490.

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.L., 1955. Hybridization between fish species in nature. Systematic Zoology 4:1-20.

Hubbs, C., T. Luciere, G.P. Garret, R.J. Edwards, S.M. Dean, and E. Marsh. 1978. Survival and abundance of introduced fishes near San Antonio, Texas. Texas Journal of Science 30(4):369-376.

Hubbs, C., R. J. Edwards, and G. P. Garrett. 1991. An annotated checklist of freshwater fishes of Texas, with key to identification of species. Texas Journal of Science, Supplement 43(4):1-56.

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.

Meffe, G. K., and F. F. Snelson, Jr., editors. 1989. Ecology and evolution of livebearing fishes (Poeciliidae). Prentice Hall, Englewood Cliffs, NJ.

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

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.

Other Resources:
Texas Freshwater Fishes - Texas State University San Marcos

FishBase Summary

Author: Leo Nico, and Matt Neilson

Revision Date: 6/28/2019

Peer Review Date: 8/23/2011

Citation Information:
Leo Nico, and Matt Neilson, 2024, Poecilia formosa (Girard, 1859): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=856, Revision Date: 6/28/2019, Peer Review Date: 8/23/2011, Access Date: 6/15/2024

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.


The data represented on this site vary in accuracy, scale, completeness, extent of coverage and origin. It is the user's responsibility to use these data consistent with their intended purpose and within stated limitations. We highly recommend reviewing metadata files prior to interpreting these data.

Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [6/15/2024].

Contact us if you are using data from this site for a publication to make sure the data are being used appropriately and for potential co-authorship if warranted.

For general information and questions about the database, contact Wesley Daniel. For problems and technical issues, contact Matthew Neilson.