The western mosquitofish, western gambusia, live-bearing tooth carp or mosquito fish ("Gambusia affinis") is a fish that belongs to the Poeciliidae family. It is from the southern and midwestern United States and east coast of Mexico. Human beings brought it to many other parts of the world, such as Hawaii, Puerto Rico, and Australia, where it has caused problems as an invasive specie. Some scientists say that the western mosquitofish has had the largest effect on the environment of any fish in Poeciliidae.