The cod icefishes are a family, Nototheniidae, of Perciform fishes, containing about 50 species in 12 genera. They are largely found in the Southern Ocean and off the coast of Antarctica. As the dominant Antarctic fish taxa, they occupy both sea bottom and water column ecological niches. Although lacking a gas bladder, they have undergone a depth-related diversification, such as increase in fatty tissues and reduced mineralization of the bones, resulting in a body density approaching neutral, to fill a variety of water column niches. It is thought that the spleen may be used to remove ice crystals from circulating blood. As the chilly subantarctic waters averages –1 to 4 degrees Celsius, most Antarctic species have antifreeze glycoproteins in their blood and other body fluids.
As the major fish resource in the Southern Ocean, nototheniids are under increasing pressure from commercial fishing.