Why Australia is not an island?
Australia (continent)
The continent includes a continental shelf overlain by shallow seas which divide it into several landmasses—the Arafura Sea and Torres Strait between mainland Australia and New Guinea, and Bass Strait between mainland Australia and Tasmania. When sea levels were lower during the Pleistocene ice age, including the Last Glacial Maximum about 18,000 BC, they were connected by dry land. During the past 10,000 years, rising sea levels overflowed the lowlands and separated the continent into today's low-lying arid to semi-arid mainland and the two mountainous islands of New Guinea and Tasmania.[2]
Freshwater fish of Australia
The small number of species found in Australian inland waters is partly because Australia is the driest continent on earth. Rainfall is sporadic over much of the continent, and fish cannot live in many of the desert regions of South Australia and Western Australia. Most freshwater species are found in tropical or subtropical regions.