Western Mosquitofish - Gambusia affinis
The only livebearer species widely distributed, the mosquitofish, is established in a thermal spring east of the Divide and can be found in other non-thermal waters in the eastern drainages during the summer. The wider summer distribution is the result of the State Board of Health planting them in mosquito-infested areas. Mosquitofish are planted because they eat crustaceans and insects on or near the water's surface, including a high number of mosquito larvae when available. Mosquitofish thus serve as a biological control for mosquitoes. Mosquitofish do not overwinter in Montana in non-thermal waters. This species shows marked sexual differences with females becoming larger than males. Females can reach about 3 inches in length.
Color is light olive to dull silver. Lateral line is absent.
Resident Year Round
Western Hemisphere Range
Observations in Montana Natural Heritage Program Database
Number of Observations:
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
(Observations spanning multiple months or years are excluded from time charts)
Year round survival in Montana is restricted to waters with thermal influences (Elser et al. 1980).
Includes all kinds of tiny aquatic plants and animals. Usually feeds at surface in very shallow water where mosquito larvae are typically found (Brown 1971).
Females larger than males.
Sexually mature in 4-6 wks. Internal fertilization. The eggs hatch internally and young emerge as free-swimming individuals. Fry produce March - Oct. in one Montana pond studied (Brown 1971).
- Literature Cited AboveLegend: View Online Publication
- Brown, C.J.D. 1971. Fishes of Montana. Montana State University, Bozeman, MT. 207 pp.
- Elser A., C. Clancy, L. Morris, M. Georges 1980 (revised). Aquatic habitat inventory of the Beaver Creek drainage and selected tributaries of the Yellowstone River. BLM report: YS-512-CT7-74. 86 pp.
- Additional ReferencesLegend: View Online Publication
Do you know of a citation we're missing?
- Land & Water Consulting, Inc., Missoula, MT., 2002, Montana Dept. of Transportation Wetland Mitigation Monitoring Report, Year 2001: Beaverhead Gateway, Dillon, Montana. Proj. No. 130091.011. July 2002. In 2001 Wetland Mitigation Monitoring Reports, Vol. I.
- Mulla, M.S. 1963. Toxicity of organochlorine insecticides to the mosquito fish Gambusia affinis and the bullfrog Rana catesbeiana. Mosquito News 23(4): 299-303.
- Additional Sources of Information Related to "Fish"