Notothenioidei

Antarctic icefish belong to the perciform suborder Notothenioidei and are the largely endemic, dominant fish taxa in the cold continental shelf waters surrounding Antarctica. At present, the suborder includes eight families with 43 genera and 122 species. Although the Southern Ocean is relatively well sampled, new species of notothenioids are still being described.

The majority of notothenioids live at seawater temperatures between −2 and 4 °C (28 and 39 °F), but some subpolar species inhabit waters that may be as warm as 10 °C (50 °F) around New Zealand and South America. Seawater temperatures below the freezing point of fresh water (0 °C or 32 °F) are possible due to the dissolved salts. Notothenioids have a depth range of about 0–1,500 m (0–4,921 ft).

The notothenioids are a relatively rare example of a marine fish species flock.

Members of the family Channichthyidae (crocodile icefish), which is part of Notothenioidei, are the only known vertebrates that do not produce red blood cells and consequently their blood lacks the normal red colour. Other families in the suborder, such as the Nototheniidae (cod icefish), do have red blood cells and studies comparing the two families have revealed genes needed to make these.