Reference Guide > Montana Fish Field Guide > Livebearers > Freshwater Drum
Western Mosquitofish - Gambusia affinis
Exotic Species (not native to montana)
Global Rank: G5
State Rank: SNA
Agency Status
USFWS: none
USFS: none
BLM: none
CFWCS Tier: 4
General Description
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.
Diagnostic Characteristics
Color is light olive to dull silver. Lateral line is absent.
Distribution
Montana Range
Resident Year Round
Habitat
Year round survival in Montana is restricted to waters with thermal influences (Elser et al. 1980).
Food Habits
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).
Ecology
Females larger than males.
Reproductive Characteristics
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).
Citations & Sources
Holton, G. D. 2003. A field guide to Montana fishes. Mont. Dept. Fish, Wildl. Parks, 95 pp.
Citation for data on this website:
Western Mosquitofish — Gambusia affinis. Montana Field Guide. Retrieved on February 2, 2009, from http://FieldGuide.mt.gov/detail_AFCNC02010.aspx
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