Notothenioidei is one of 19 suborders of the order

Perciformes Perciformes (), also called the Percomorpha or Acanthopteri, is an order or superorder of ray-finned fish. If considered a single order, they are the most numerous order of vertebrates, containing about 41% of all bony fish. Perciformes means ...

. The group is found mainly in Antarctic and

Subantarctic The sub-Antarctic zone is a region in the Southern Hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° and 60° south of the Equator. The subantarctic region includes many islands ...

waters, with some species ranging north to southern Australia and southern

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

. Notothenioids constitute approximately 90% of the fish biomass in the continental shelf waters surrounding

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

Evolution and geographic distribution

The

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...

has supported fish habitats for 400 million years; however, modern notothenioids likely appeared sometime after the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

epoch. This period marked the cooling of the Southern Ocean, resulting in the stable, ice-cold conditions that have persisted to the present day. Another key factor in the evolution of notothenioids is the preponderance of the Antarctic Circumpolar Current (ACC), a large, slow-moving current that extends to the seafloor and precludes most migration to and from the Antarctic region. These unique environmental conditions in concert with the key evolutionary innovation of Antifreeze glycoprotein promoted widespread radiation within the suborder, leading to the rapid development of new species. Their adaptive radiation is characterized by depth related diversification. Comparison studies between non-Antarctic and Antarctic species have revealed different ecological processes and genetic differences between the two groups of fish, such as the loss of

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyt ...

(in the family

Channichthyidae The crocodile icefish or white-blooded fish comprise a family (Channichthyidae) of notothenioid fish found in the Southern Ocean around Antarctica. They are the only known vertebrates to lack hemoglobin in their blood as adults. Icefish populatio ...

) and changes in buoyancy. They are distributed mainly throughout the

around the coasts of

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

, southern

, and

. An estimated 79% of species reside within the Antarctic region. They primarily inhabit seawater temperatures between −2 and 4 °C (28 and 39 °F); however, some of the non-Antarctic species inhabit waters that may be as warm as 10 °C (50 °F) around New Zealand and South America. Seawater temperatures below the freezing point of freshwater (0 °C or 32 °F) are possible due to the greater salinity in the Southern Ocean waters. Notothenioids have an estimated depth range of about 0–1,500 m (0–4,921 ft).

Anatomy

Notothenioids display a

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

that is largely typical of other coastal

perciform Perciformes (), also called the Percomorpha or Acanthopteri, is an order or superorder of ray-finned fish. If considered a single order, they are the most numerous order of vertebrates, containing about 41% of all bony fish. Perciformes means " ...

fishes. They are not distinguished by a single physical trait, but rather a distinctive set of morphological traits. These include the presence of three flat

pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

radials, nostrils located laterally on each side of the head, the lack of a swim bladder, and the presence of multiple lateral lines. Because notothenioids lack a swim bladder, the majority of species are benthic or demersal in nature. However, a depth-related diversification has given rise to some species attaining increased buoyancy, using

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...

deposits in tissues and reduced

ossification Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in ...

of bony structures. This reduced ossification of the skeleton (observed in some notothenioids) changes the weight and creates neutral buoyancy in the water, where the fish neither sinks nor floats, and can thus adjust its depth with ease.

Physiology

Notothenioids have a variety of physiological and biochemical

adaptations In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the ...

that either permit survival in, or are possible only because of, the generally cold, stable seawater temperatures of the Southern Ocean. These include highly unsaturated

membrane lipids Membrane lipids are a group of compounds (structurally similar to fats and oils) which form the double-layered surface of all cells (lipid bilayer). The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol. Lipid ...

and metabolic compensation in enzymatic activity. Many notothenoids have lost the nearly universal heat shock response (HSR) due to evolution at cold and stable temperatures. Many notothenioid fishes are able to survive in the freezing, ice-laden waters of the Southern Ocean because of the presence of an antifreeze glycoprotein in blood and body fluids. Although many of the Antarctic species have antifreeze proteins in their body fluids, not all of them do. Some non-Antarctic species either produce no or very little antifreeze, and antifreeze concentrations in some species are very low in young, larval fish. While the majority of animal species have up to 45% of

(or other oxygen-binding and oxygen-transporting pigments) in their blood, the notothenioids of the family

do not express any

globin The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. These proteins all incorporate the globin fold, a series of eight alpha helical segments. Two prominent members include myogl ...

proteins in their blood. As a result, the oxygen-carrying capacity of their blood is reduced to less than 10% that of other fishes. This trait likely arose due to the high oxygen solubility of the Southern Ocean waters. At cold temperatures, the oxygen solubility of water is enhanced. The loss of hemoglobin is partially compensated in these species by the presence of a large, slow-beating heart and enlarged blood vessels that transport a large volume of blood under low pressure to enhance cardiac output. Despite these compensations, the loss of globin proteins still results in reduced physiological performance.

Systematics

Naming

Notothenioidei was first described as a separate grouping, as a "division" he named Nototheniiformes, by the British ichthyologist Charles Tate Regan in 1913., this subsequently has been considered as a suborder of the Percifomes. The name is based on the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

''Notothenia'', a name coined by Sir John Richardson in 1841 and which means “coming from the south”, a reference to the Antarctic distribution of the genus.

Families

This classification follows Eastman and Eakin, 2000 and includes references to additional classified species.Froese, Rainer, and Daniel Pauly, eds. (2013). Species of ''Channichthys'' in FishBase. February 2013 version. Most species are restricted to the vicinity of Antarctica. * Family Bovichtidae

Gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

, 1862 ** Genus ''

Bovichtus ''Bovichtus'' is a genus of fish in the family Bovichtidae found in the Atlantic, Indian and Pacific Ocean. Taxonomy ''Bovichtus'' was formally described as a genus in 1832 by the French zoologist Achille Valenciennes with ''Callionymus diacanth ...

Valenciennes Valenciennes (, also , , ; nl, label=also Dutch, Valencijn; pcd, Valincyinnes or ; la, Valentianae) is a commune in the Nord department, Hauts-de-France, France. It lies on the Scheldt () river. Although the city and region experienced a ...

, 1832 ** Genus ''

Cottoperca ''Cottoperca'' is a genus of marine ray-finned fishes belonging to the family Bovichtidae, the temperate icefishes or thornfishes. They are found in the southeastern Pacific, southwestern Atlantic and northern Southern Oceans off southern South A ...

'' Steindachner, 1875 ** Genus ''

Halaphritis The flathead congoli (''Halaphritis platcephala'') is a species of marine ray-finned fish, belonging to the family Bovichtidae, the thornfishes or temperate icefishes. It is native to the seas off southeastern Australia. This species is the onl ...

Last A last is a mechanical form shaped like a human foot. It is used by shoemakers and cordwainers in the manufacture and repair of shoes. Lasts typically come in pairs and have been made from various materials, including hardwoods, cast iron, an ...

, Balushkin & Hutchins, 2002 * Family

Pseudaphritidae The congoli (''Pseudaphritis urvillii''), also known as the freshwater flathead, marble fish, marbled flathead, sand trout, sanding, sandy, sandy whiting or tupong. is a species of marine ray-finned fish and it is the only species of fish in t ...

McCulloch McCulloch is a Scottish surname. It's a variation of the Northern Irish surname McCullough. It's commonly found in Galloway. Notable people with the surname include: *Alan McCulloch (politician), New Zealand politician *Alan McLeod McCulloch ( ...

, 1929 ** Genus ''

Pseudaphritis The congoli (''Pseudaphritis urvillii''), also known as the freshwater flathead, marble fish, marbled flathead, sand trout, sanding, sandy, sandy whiting or tupong. is a species of marine ray-finned fish and it is the only species of fish in t ...

'' Castelnau, 1872 * Family Eleginopsidae Gill, 1893 ** Genus ''

Eleginops The Patagonian blennie (''Eleginops maclovinus''), also known as the rock cod, is a species of marine ray-finned fish, belonging to the monotypic family Eleginopidae and monotypic genus ''Eleginops''. It is found in coastal and estuarine habitat ...

'' Gill, 1862 * Family

Nototheniidae : ''In some scientific literature, the term "cod icefish" is used to identify members of this family. This should not be confused with the term "icefish," which refers to the "white-blooded" fishes of the family Channichthyidae. See Icefish (disam ...

Günther, 1861 ** Genus '' Aethotaxis'' H. H. DeWitt, 1962 ** Genus '' Cryothenia'' Daniels, 1981 ** Genus ''

Dissostichus ''Dissostichus'', the toothfish, is a genus of marine ray-finned fish belonging to the family Nototheniidae, the notothens or cod icefish. These fish are found in the Southern Hemisphere. Toothfish are marketed in the United States as Chilean ...

'' Smitt, 1898 ** Genus '' Gobionotothen'' Balushkin, 1976 ** Genus '' Gvozdarus'' Balushkin, 1989 ** Genus '' Lepidonotothen'' Balushkin, 1976 ** Genus '' Lindbergichthys'' Balushkin, 1979 ** Genus ''

Notothenia ''Notothenia'' is a genus of marine ray-finned fishes belonging to the family Nototheniidae, the notothens or cod icefishes with the species in this genus often having the common name of rockcod. They are native to the Southern Ocean and other wa ...

'' Richardson, 1844 ** Genus '' Nototheniops'' Balushkin, 1976 ** Genus '' Pagothenia''

Nichols Nichols may refer to: People *Nichols (surname) *Nichol, a surname Places Canada * Nichols Islands, Nunavut United States * Nichols, California, an unincorporated community * Nichols Canyon, Los Angeles, California * Nichols, Connecticut * Nich ...

& La Monte, 1936 P ** Genus '' Paranotothenia'' Balushkin, 1976 ** Genus '' Patagonotothen'' Balushkin, 1976 ** Genus ''

Pleuragramma The Antarctic silverfish (''Pleuragramma antarctica''), or Antarctic herring, is a species of marine ray-finned fish belonging to the Family (biology), family Nototheniidae, the notothens or cod icefishes. It is native to the Southern Ocean and t ...

'' Balushkin, 1982 ** Genus ''

Trematomus ''Trematomus'' is a genus of marine ray-finned fishes, belonging to the Family (biology), family Nototheniidae, the notothens or cod icefishes. These fishes occur in the Southern Ocean. Taxonomy ''Trematomus'' was first described as a genus in 1 ...

'' Boulenger, 1902 * Family Harpagiferidae Gill, 1861 ** Genus '' Harpagifer'' Richardson, 1844 * Family Artedidraconidae Andriashev, 1967 ** Genus '' Artedidraco'' Lönnberg, 1905 ** Genus '' Dolloidraco'' Roule, 1913 ** Genus '' Histiodraco'' Regan, 1914 ** Genus '' Pogonophryne'' Regan, 1914 * Family Bathydraconidae Regan, 1913 ** Genus '' Acanthodraco'' Skóra, 1995 ** Genus '' Akarotaxis'' DeWitt & Hureau, 1980 ** Genus '' Bathydraco'' Günther, 1878 ** Genus '' Cygnodraco'' Waite, 1916 ** Genus '' Gerlachea'' Dollo, 1900 ** Genus '' Gymnodraco'' Boulenger, 1902 ** Genus '' Parachaenichthys'' Boulenger, 1902 ** Genus '' Prionodraco'' Regan, 1914 (one species) ** Genus '' Psilodraco'' Norman. 1937 ** Genus '' Racovitzia'' Dollo, 1900 ** Genus '' Vomeridens'' DeWitt & Hureau, 1980 * Family

Gill, 1861 ** Genus '' Chaenocephalus'' Richardson, 1844 ** Genus ''

Chaenodraco ''Chaenodraco wilsoni'', the spiny icefish, is a species of marine ray-finned fish belonging to the family Channichthyidae, the crocodile icefishes. It is native to the Southern Ocean. This species is the only known member of its genus. It is of m ...

'' Regan, 1914 ** Genus '' Champsocephalus'' Gill, 1861 (two species) ** Genus '' Channichthys'' Richardson, 1844 ** Genus '' Chionobathyscus'' Andriashev & Neyelov, 1978 ** Genus '' Chionodraco'' Lönnberg, 1905 ** Genus '' Cryodraco'' Dollo, 1900 ** Genus '' Dacodraco'' Waite, 1916 ** Genus ''

Neopagetopsis Jonah's icefish (''Neopagetopsis ionah'') is a benthopelagic species of marine ray-finned fish belonging to the family Channichthyidae, the crocodile icefishes. It is the only member of the monotypic genus ''Neopagetopsis''. It is found in the Sou ...

'' Nybelin, 1947 ** Genus '' Pagetopsis'' Regan, 1913 ** Genus '' Pseudochaenichthys'' Norman, 1937