What are fishes?

Fish are aquatic vertebrates that:

  • breathe using gills
  • lack fully developed limbs
  • swim with the aid of fins (when these are present).

They form by far the largest group of vertebrates in the world. The two main groupings that make up fishes in Australian waters are the Agnatha, or jawless fishes (hagfishes and lampreys) and Gnathostomata, which includes the classes Chondrichthyes (chimaeras, sharks and rays), Sarcopterygii (lungfish), and Actinopterygii (ray-finned fishes). Fishes are found in virtually all aquatic environments, from mountain streams and desert springs, to the deep sea.

There is enormous diversity in the size, shape and mode of reproduction in fishes. Scales, fins, teeth and even eyes may variously be present or absent, depending on species. Some species are found in all oceans of the world, while others may be restricted to a particular habitat within a single stream. The types of habitat fish occupy and their tolerance to extremes in temperature, pH and salinity also varies greatly according to species. Some are capable of living in temperatures below freezing, while others have been recorded in hot springs of more than 40º C.

Australia has a large and highly diverse range of fishes relative to the rest to the world. It is home to an estimated 4,800 of a total of about 32,500 species worldwide.

Queensland Museum's Find out about... is proudly supported by the Thyne Reid Foundation and the Tim Fairfax Family Foundation.