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