Australia is the driest inhabited continent so it is no surprise that it has fewer species of freshwater fish than any other continent, with the obvious exception of Antarctica. Australia has the lowest rainfall in proportion to its land area and the least surface runoff.
There are only about 302 different species of freshwater fish native to Australia.
The Western Plateau of Australia includes the Gibson and the Great sandy deserts and covers about 2,700,000 square kilometres. Fish are unknown in this vast area.
Tasmania, Australia’s island state, is geographically and politically part of Australia, but geologically is completely different. While Australia is the flattest continent, Tasmania is one of the most mountainous islands in the world.
The mountains that perhaps should have been part of Australia are in the island of New Guinea. Politically, the western part of New Guinea is the independent State of Papua New Guinea and the western part is Irian Jaya, owned by Indonesia.
Unlike the Australian continent, both Tasmania and New Guinea are wet places with plenty of fish.
The ancestors of most of Australia’s fish were marine fish only a few million years ago, but Australia has a few fish of extremely ancient linage, including the Queensland Lungfish, Neoceratodus foreteri. This fish seems morphologically surprisingly similar to lung fish fossils from 380 million years ago. The ancestor of the terrestrial vertebrates was probably rather like this fish.
The name rainbow fish has been used for many different fish. The rainbow fish of Australia and New Guinea are small colourful fish from the Melanotaenlidae family. There are sixty-six species from seven genera. They mainly come from New Guinea and the northern parts of Australia, with the notable exception of the Murray River Rainbow fish, Melanotaenia fluviatilis. This fish is found much further south than any other species of Australian Rainbow Fish.