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.

Nototheniidae, the notothens or cod icefishes, is a family of ray-finned fishes, part of the suborder Notothenioidei which is traditionally placed within the order Perciformes. They are largely found in the Southern Ocean.