Mosquitofish

Gambusia affinis

Gambusia affinis, the western mosquitofish, is a small freshwater livebearer in the family Poeciliidae. Adults are tiny, with females reaching about 7 cm and males only about 3.5 cm. They have an olive-grey body, a slightly upturned mouth adapted for surface feeding, and a rounded caudal fin. Males possess a modified anal fin (gonopodium) for internal fertilization. This species is native to the southeastern United States and northern Mexico at depths of 0-2 meters in freshwater habitats, but has been introduced to over 60 countries worldwide for mosquito control. They inhabit virtually any warm freshwater habitat including ponds, ditches, streams, and marshes. Mosquitofish are voracious predators of mosquito larvae and other small insects at the water surface. As livebearers, females can produce multiple broods without re-mating. While effective at mosquito control, they are considered one of the world's most invasive fish species, often outcompeting native fish.