Upwelling
The major upwellings in the ocean are associated with the divergence of currents that bring deeper, colder, nutrient rich waters to the surface. There are at least five types of upwelling: coastal upwelling, large-scale wind-driven upwelling in the ocean interior, upwelling associated with eddies, topographically-associated upwelling, and broad-diffusive upwelling in the ocean interior.
Fauna of Australia
More than 5000 species of fish inhabit Australia's waterways; of these, 24% are endemic. However, because of the relative scarcity of freshwater waterways, Australia has only about 300 species of freshwater fish. Two families of freshwater fish have ancient origins: the arowana or bonytongues, and the Queensland lungfish. The Queensland lungfish is the most primitive of the lungfish, having evolved before Australia separated from Gondwana. One of the smallest freshwater fish, peculiar to the southwest of Western Australia, is the salamanderfish, which can survive desiccation in the dry season by burrowing into mud. Other families with a potentially Gondwanan origin include the Retropinnidae, Galaxiidae, Aplochitonidae and Percichthyidae. Apart from the ancient freshwater species, 70% of Australia's freshwater fish have affinities with tropical Indo-Pacific marine species that have adapted to freshwater. These species include freshwater lampreys, herrings, catfish, rainbowfish, and some 50 species of gudgeon, including the sleepy cod. Native freshwater game fish include the barramundi, Murray cod, and golden perch. Two species of endangered freshwater shark are found in the Northern Territory.
Several exotic freshwater fish species, including brown, brook and rainbow trout, Atlantic and Chinook salmon, redfin perch, common carp, and mosquitofish, have been introduced to Australian waterways. The mosquitofish is a particularly aggressive species known for harassing and nipping the fins of other fish. It has been linked to declines and localised extirpations of several small native fish species. The introduced trout species have had serious negative impacts on a number of upland native fish species including trout cod, Macquarie perch and mountain galaxias species as well as other upland fauna such as the spotted tree frog. The common carp is strongly implicated in the dramatic loss in waterweed, decline of small native fish species and permanently elevated levels of turbidity in the Murray-Darling Basin of south west Australia.