The Antarctic toothfish, also known as the Antarctic cod, is a large, black or brown fish found in very cold (subzero) waters of the Southern Ocean near Antarctica. It is the largest fish in the Southern Ocean, feeding on shrimp and smaller fish, and preyed on by whales, orcas, and seals. It is caught for food and marketed as Chilean sea bass together with its sister species, the more northerly Patagonian toothfish. Often mistakenly called "Antarctic cod", the Antarctic toothfish belongs to the notothen family (Nototheniidae), a family of fish genera that are abundant near Antarctica.

The Patagonian toothfish, also known as Chilean sea bass, mero, icefish, and Antarctic cod, is a species of notothen found in cold waters between depths of 45 and 3,850 m in the southern Atlantic, Pacific, and Indian Oceans and Southern Ocean on seamounts and continental shelves around most Subantarctic islands.