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.

Heterandria formosa
Heterandria formosa
(Least Killifish)
Native Transplant

Copyright Info
Heterandria formosa Girard, 1859

Common name: Least Killifish

Synonyms and Other Names: dwarf livebearer

Taxonomy: available through www.itis.govITIS logo

Identification: Menhinick (1991); Page and Burr (1991); Mettee et al. (1996).

Size: females to 3.0 cm SL

Native Range: Lower Coastal Plain from South Carolina to southern Louisiana (Rosen 1979; 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 Heterandria formosa are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
FL198819881Vero Beach
NJ190519051Great Egg Harbor
NC197820112Cape Fear; Northeast Cape Fear
SC201920191Coastal Carolina

Table last updated 2/20/2024

† Populations may not be currently present.

Ecology: Heterandria formosa is one of the smallest freshwater fish species in North America, with females maturing at 15 mm SL (Bennett and Conway 2010). Inhabits still waters of pools and slow-moving streams in areas of dense vegetation (Boschung and Mayden 2004). Dwarf killifish are omnivorous, generally consuming aquatic invertebrates (ostracods, copepods, and cladocerans) but will also consume plant materal as well (Boschung and Mayden 2004).

Means of Introduction: In 1905 about 10,000 Heterandria and Gambusia were stocked into New Jersey for mosquito control purposes (Seal 1910). The reason for the North Carolina stocking is not known.

Status: The New Jersey population apparently did not survive; the species is established in North Carolina.

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: Seal (1910) did not provide the locality or localities in New Jersey where he stocked fish, although he did mention that at least one of the sites was some 90 miles from Cape May. Krumholz (1948) indicated that the fish stocked in New Jersey came from North Carolina, but that information does not appear in Seal (1910). The isolated population near Wilmington, North Carolina, is similar to the distribution of Lucania goodei, another species listed by Menhinick (1991) as introduced. These similar distributions could indicate a shared transport event, or conversely, a shared refugium (Starnes, personal communication).

References: (click for full references)

Bennett, M.G., and K.W. Conway. 2010. An overviwe of North America's diminutive freshwater fish fauna. Ichthyological Exploration of Freshwaters. 21(1):63-72.

Boschung, H.T., Jr. and R.L. Mayden. 2004. Fishes of Alabama. Smithsonian Books, Washington, D.C.

Krumholz, L. A. 1948. Reproduction in the western mosquito fish, Gambusia affinis affinis (Baird and Girard), and its use in mosquito control. Ecological Monographs 18:1-43.

Menhinick, E. F. 1991. The freshwater fishes of North Carolina. North Carolina Wildlife Resources Commission. 227 pp.

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.

Seal, W. P. 1910. Fishes in their relation to the mosquito problem. Bulletin of the U.S. Bureau of Fisheries 28(1908):831-838.

Other Resources:
FishBase Summary

Author: Leo Nico, Pam Fuller, and Matt Neilson

Revision Date: 6/27/2011

Peer Review Date: 6/27/2011

Citation Information:
Leo Nico, Pam Fuller, and Matt Neilson, 2024, Heterandria formosa Girard, 1859: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=852, Revision Date: 6/27/2011, Peer Review Date: 6/27/2011, Access Date: 2/20/2024

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 [2/20/2024].

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