The Tasmanian giant freshwater crayfish (Astacopsis gouldi) is the largest freshwater invertebrate in the world. The species is only found in Tasmania (an Australian island), and is listed as an endangered species due to habitat loss and over fishing. It is also severely threatened by siltation and de-snagging of streams as decaying wood forms the favourite part of its diet. It is not known if the animals are nourished by the wood, the bacteria, algae or invertebrates living in the rotting logs. They also eat leaves, fish and other meat, including other freshwater invertebrates.
Individuals of over 5 kilograms (11 lb) in weight and over 80 centimetres (31 in) long have been known in the past, but now, even individuals over 2 kilograms (4.4 lb) are rare. The species is only found in Tasmanian rivers flowing north into the Bass Strait (with the exception of the Tamar) below 400 metres (1,300 ft) above sea level, and is listed as an endangered species on the IUCN Red List. The specific epithet gouldi commemorates the Australian naturalist John Gould.

These crustaceans inhabit dark, slow-moving rivers and streams with high water quality and little suspended sediment, as well as still, deep pools with logs and overhanging banks to shelter beneath. The water needs to be below 18°C with high oxygen content.

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