Stewardship Overview: The spread of mosquitofish outside its native range should be monitored and necessary steps taken to: (1) understand the competitive edge it has over native species, (2) limit its introduction or invasion into new locations, and (3) evaluate the possible benefit of eradication efforts in locations that can be rehabilitated for native fishes.
Species Impact: Outside their native range, mosquitofish play a role in decreasing populations of native fishes (Miller 1961, Myers 1965, Minckley and Deacon 1968). Due to the number of introductions and corresponding decreases in native fish populations, there can be no doubt of the destructive nature of such introductions. Myers (1965) wrote that almost everywhere introductions have been made, mosquitofish have gradually eliminated or reduced populations of small native fishes. For example, mosquitofish have been instrumental in eliminating native populations of Poeciliopsis occidentalis in the southwestern U.S. (Sublette et al. 1990); P. occidentalis may be effectively eliminated in 1-3 years (Meffe 1984). Evermann and Clark (1931) reported that mosquitofish in the Salton Sea, California, drove out Cyprinodon macularius less than 10 years after introduction to the state. The mechanism for many of these reductions is believed to be predation (Meffe 1985, Courtenay and Meffe 1989). Myers (1965) reported that mosquitofish have even reduced largemouth bass (Micropterus salmoides) and carp (Cyprinus carpio) populations due to predation on larvae. Another problem is caused when mosquitofish hybridize with other Gambusia species (Yardley and Hubbs 1976, Rutherford 1980). Intergradation then corrupts the genome of the native species.
Introduced mosquitofish also prey heavily on amphibian larvae (Goodsell and Kats 1999) and potentially negatively impact salamander and frog populations (Lawler et al. 1999).