Two hundred species of fish have been recorded south of the Antarctic Convergence. Many of them, especially those of the coastal waters, are endemic to the region, occurring nowhere else and adapted to the extreme conditions. They tend to be slow-growing. Five families in the order Notothenioidea make up 75% of the Antarctic fish fauna, four of them found only south of the Convergence, isolated there for millions of years. The Antarctic cod Notothenia coriiceps is the largest fish in this region, as long as 1.5m (5ft) and with an average weight of over 25kg (55lb), although large specimens may reach 70kg (154lb). They are found in the deep waters of the Ross Sea.
Plunder fish tend to be small, within the 10–30cm (4–12in) range. They are scaleless, with characteristically long barbells on the lower jaw. Most of them live near the bottom on the continental shelf. The Antarctic spiny plunder fish Harpagifer antarcticus is found in shallow water round the northern end of the peninsula but is common in tide pools in South Georgia. The dragon fish are elongate animals up to 50cm (20in) long, with snouts like pike and lacking the first dorsal fin. Most have been caught near the bottom in deep water.
One genus, Pleurogramma, includes the Antarctic herring, the only truly pelagic plankton-eating fish. Antarctic fish have developed extreme adaptations to the near-freezing water. (One species, Trematomus bernacchii, actually lives under the fast-ice.) They have glycoproteins – antifreeze proteins – in the blood and body tissues.
One large and predatory group, the ice fish, is unique in having no red blood cells. Lacking the oxygen carried by haemoglobin and myoglobin, they manage because the cold Antarctic water is well oxygenated. The clear blood and pale anaemic flesh of these fish give them their family name; even the gills are cream coloured, in contrast to the red gills of most fish.