Western Mosquitofish

Scientific Name: Gambusia affinis


Robert McDowallCopyright Info

Identification: The western mosquitofish is dull grey or brown in color and has a rounded tailfin. Its body is short, its head is flattened, and its mouth points upward for surface feeding.


Size: This species is 2.5 inches (6.5 cm) in length.


Native Range: The western mosquitofish is native to coastal drainages from southern New Jersey to Mexico and to the Mississippi River Basin from central Indiana and Illinois south to the Gulf of Mexico.


Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, 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 Gambusia affinis are found here.

Full list of USGS occurrences

State/ProvinceYear of earliest observationYear of last observationTotal HUCs with observations†HUCs with observations†
Michigan196120133Detroit; Great Lakes Region; Lake Erie
Ohio194720092Black-Rocky; Lower Maumee

Table last updated 10/4/2018

† Populations may not be currently present.


Means of Introduction: This species has been stocked in temperate and tropical areas around the world because of its reputation as a mosquito-control agent. The western mosquitofish was first distributed in the United States in the early 1900s. It was widely introduced during the following decades because this species was thought to be an effective and inexpensive means of combating malaria, a mosquito-borne disease. Many state and local health departments continue to view the use of western mosquitofish as an attractive alternative to insecticides. However, in some areas, western mosquitofish has spread to sites far from where it was originally introduced.


Status: The western mosquitofish has been stocked and established in most states outside of their native range. Its establishment and spread in northern states is greatly restricted because the western mosquitofish does not tolerate cold weather. In most cases, surviving the winter in colder regions requires isolated habitats where water is warmer.


Author: Illinois-Indiana Sea Grant


Contributing Agencies:
NOAA Sea Grant GLRI Logo


Revision Date: 9/25/2012


Citation for this information:
Illinois-Indiana Sea Grant, 2019, Western Mosquitofish: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatLakes/FactSheet.aspx?SpeciesID=846&Potential=N&Type=1&HUCNumber=, Revision Date: 9/25/2012, Access Date: 8/23/2019

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.