A tiny fish up to only 5cm in length. Very widespread and abundant throughout southern Australia including the Murray Darling basin and Gulf drainages, preferring still, warm waters adjacent aquatic vegetation. Was introduced into Australia in the 1920's for mosquito control, but proved to less effective in the control of mosquitos than many native fishes (The species is sometimes referred to as Mosquitofish, but due to its poor performance in regards to predating upon mosquito's and that it is a threat to native species this common name is no longer preferred.).

The Eastern gambusia is from a large and diverse family called Poeciliidae. All of which are characterised by their habit of giving birth to live young, rather than laying eggs. Following birth the fish grows very rapidly and can mature in less than two months. Furthermore, the species is able to breed several times a year. The result being that populations can grow very rapidly.

The Eastern gambusia is considered a threat to many other native fishes because it predates upon the eggs and young fish. It is also known to intimidate other native fishes by nipping at their fins thus affecting behaviour and contributing to mortality by increasing susceptibility to disease.