mosquito fish

:  either of two small, surface-feeding, freshwater fishes (Gambusia affinis and G. holbrooki of the family Poeciliidae) native to Central and North America that are live-bearers and are widely introduced outside their native range to control mosquitoes by feeding on their larvae York County has been populating water sources and backyard ponds with mosquito fish, a small guppy-like swimmer that devours mosquito larvae, for more than 25 years. — Amanda Williams