Gambusia holbrooki Girard, 1859
The Eastern Gambusia can be recognised by its dorsally flattened head, small, upturned mouth, large eyes, rounded tail and single dorsal fin.
It is green to brown on the back, grey with a bluish sheen on the sides and silvery-white on the belly.
Adult females are much larger than males. The female grows to 60 mm in length and often has a black mark on the side of the belly above the vent. Males grow to 35 mm and have a large gonopodium. This structure (clearly visible in both images) is formed by the thickened anal fin rays, and is used for sperm transfer to the female.
The Eastern Gambusia is native to the rivers of south-eastern America, but was introduced into Australia in the 1920s. Its reputation as a mosquito eater is responsible for one of its common names, Mosquitofish. In Australia, however the Eastern Gambusia appears no more effective at controlling mosquito populations than native fishes.
Its wide range of food items include ants, flies, aquatic bugs and beetles.
This species is now widespread in fresh coastal and inland waters of New South Wales, Victoria, and South Australia. It is also recorded from coastal drainages of Queensland and parts of the Northern Territory and Western Australia.
http://www.amonline.net.au/fishes/fishfacts/fish/gholbrooki.htm
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