Eastern Gambusia has been declared a controlled fish under the Inland Fisheries Act 1995. Controlled fish may not be imported, moved or kept in this State and there are heavy fines for doing so. This fish, which is also known as Mosquito fish, is considered a noxious pest in most states of Australia. It has the potential to spread into new habitats, forming dense populations and impacting heavily on native fish, invertebrates and frog populations.
Upturned mouth. No lateral line. Single dorsal fin. Eyes are large. Female is deeper in the body with a much deeper stomach and a large black blotch at the rear of the belly. The male is clearly distinguished by the very long rays of the anal fin.
Upper body colour is dark brown to bluish-brown or greenish, sides are grey and the belly is white.
Females grow to a maximum length of 6cm, males rarely exceed 3.5cm.
These fish are native to North America and were introduced to Australia in 1925 to assist with mosquito control. Unfortunately, they are not effective at controlling mosquitoes and have the potential to impact heavily on other fish species. The main reasons for the latter are: that they have an effective breeding strategy, bearing live young not eggs; they are particularly aggressive for a small fish and will predate upon and compete for food with native fish species; and they are hardy, being able to withstand a wide range of water temperatures (3 to 41oC), oxygen levels and salinities. Gambusia have been implicated in the decline of several small native fish species, and there is evidence to suggest that they can have a significant impact on frog populations.
In 1991, an established population was discovered in a farm dam in the Tamar River catchment. The IFS attempted to eradicate the population using fish poison, however, by 2001 the population had re-established itself and was discovered in two nearby locations.