see text 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.

[3] They are traditionally placed in the order Perciformes together with their relatives,[4] Actual phylogenetic relationships among species of suborder Notothenioidei have not yet been determined with certainty.

The family comprises about 50 species of fish that are adapted to living in the cold, nutrient-rich waters of the Southern Ocean.

The Nototheniidae family includes some of the most ecologically and evolutionarily important fish in the Antarctic ecosystem, making them a crucial subject for scientific study.

Due to their abundance in the Southern Ocean, Nototheniidae is an important part of the food chain for many marine predators, including seals, whales, and birds.

[citation needed] Nototheniidae species have no swim bladder, however, they have other depth-related adaptations, such as increased fatty tissues and reduced mineralization of the bones, resulting in a body density approaching neutral, to fill a variety of niches.

[9][10] As the chilly Antarctic and sub-Antarctic waters of the Southern Ocean average −1 to 4 °C (30–39 °F),[11] most species of these regions produce antifreeze glycoproteins to prevent the formation of ice crystals in blood and other body fluids.