Nototheniidae
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.
Nototheniidae was described as a family in 1861 by the German-born British ichthyologist Albert Günther with the type genus being Notothenia which had been described in 1844 by Sir John Richardson with the species Notothenia coriiceps which Richardson had also described in 1844 subsequently being designated as the type in 1862 by Theodore Nicholas Gill.[2] The name Notothenia means “coming from the south”, a reference to the Antarctic distribution of the genus.[3] They are traditionally placed in the order Perciformes together with their relatives,[4] Phylogenetic analysis of morphological characters has revealed that the family Bovichtidae may not be a monophyletic group.[5] but like every lineage in the order, actual phylogenetic relationships among these species have not yet been determined with certainty.[6]
Nototheniidae fishes have fusiform or elongate and oblong bodies. They typically have two dorsal fins, the first having 3 to 11 spines and the second having 25-42 segmented fin rays. The anal fin is similar to the second dorsal fin and has 22 to 40 segmented rays. All but the last dorsal and anal fin rays are branched. The caudal fin is rounded to forked and the pectoral fins are large. The mouth is terminal and may be horizontal or angled with a protrusible upper jaw. There are no teeth on the roof of the mouth. in most species there are no spines on the preoperculum or operculum. Any scales are usually ctenoid although the spinules may be reduced or absent. They have between 1and 3 lateral lines.[8] They vary in size from. Total length of 11 cm (4.3 in) in Patagonotothen cornucola to 215 cm (85 in) in the Patagonian toothfish (Dissostichus eleginoides).[7]
Nototheniidae species are largely found in the Southern Ocean and are particularly abundant off the shores of Antarctica.[8] As the dominant Antarctic fish taxa, they occupy both sea-bottom and water-column ecological niches.[9]
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] The spleen may be used to remove ice crystals from circulating blood.[10][11] As the chilly Antarctica and sub-Antarctic waters of the Southern Ocean average −1 to 4 °C (30–39 °F),[12] most species of these regions produce antifreeze glycoproteins to prevent the formation of ice crystals in blood and other body fluids.[13]
Some species exhibit polymorphism, for example, the circum-Antarctic Trematomus newnesi exists as two morphs in the Ross Sea, the typical morph and a large-mouthed/broad-headed morph.[14]
