This species was deliberately introduced under government control in an attempt to control mosquito numbers and to help prevent the spread of some human diseases. Unfortunately, gambusia have an extremely effective breeding strategy, being live bearers, out compete native fish especially in degraded systems and harass and nip the fins of other small fish. Gambusia has been implicated in the decline of several small native species. On top of all that, it is highly debatable that the gambusia is even as good a predator of mosquitoes as the fish it has displaced!
Gambusia are a declared noxious species in Victoria and it is illegal to hold or translocate the fish.