a small gambusia fish (Gambusia affinis) sometimes introduced into a body of water to control mosquito larvae
or mosquito fish
nounpl. mosquitofish or mos·qui·to·fish·es or mosquito fish or mosquito fish·es
Any of various fishes that feed on the larvae of mosquitoes, especially a small gambusia (Gambusia affinis) native to Mexico and the eastern United States but widely introduced elsewhere for use in controlling mosquitoes.
(plural mosquitofishes or mosquitofish)