Fish and cephalopods (squid and octopus) in the Antarctic are important components of the benthic and pelagic marine ecosystems. They are major prey for higher predators, including whales and seals and seabirds.
The Antarctic fish fauna is unusual in being dominated by the radiation of small number of groups. The most striking radiation is that of the so-called Antarctic cods (not related to true cods), the Notothenioids, which dominate the continental shelves. Antarctic Nototheniid fish, living in close proximity to ice, have evolved a glycoprotein antifreeze in their body fluids to prevent freezing. In deeper waters there are also significant radiations of snail-fishes (Liparidae) and eel-pouts (Zoarcidae).
The Antarctic fish fauna contains the unique vertebrate group the Channichthyidae or icefish (so called because of their pale colouration). These fish are the only group of vertebrates which have no red blood pigment (haemoglobin). Oxygen is transported instead in solution in the blood plasma. The mackerel icefish (Champsocephalus gunnari) is important prey for Antarctic fur seals, and is the subject of a closely regulated commercial fishery.
Fish in the Southern Ocean have been or are subject to commercial exploitation. Since 1990 the most important species of fish commercially has been the Patagonian toothfish (Dissostichus eleginoides), which is taken on long lines set in around 1,000 metres at the shelf break. Unfortunately, this long-line fishery is responsible for a high incidental mortality of albatrosses and petrels.
Squid range in size from the small (15cm) Brachioteuthis to the enormous (4 metres) Mesonychoteuthis, which has large hooks as well as suckers on its arms and tentacles for capturing prey. The octopuses are less well known. Despite the fact they are very common, there are undoubtedly many species in Antarctic benthic ecosystems that are currently unknown to science.
Large fisheries for squid occur in waters adjacent to the Antarctic. Commercially exploitable squid live in Antarctic waters and exploratory fishing for them has already taken place. If full-scale fishing develops, it will require management under precautionary principles by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) because of the risk to dependent predators.