Notothenioidei is one of 19 suborders of the order Perciformes. The group is found mainly in Antarctic and Subantarctic 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 souther ...

. 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 co ...

Evolution and geographic distribution

The Southern Ocean 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 (in the family Channichthyidae) and changes in buoyancy. They are distributed mainly throughout the Southern Ocean 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 List of islands of New Zealand, smaller islands. It is the ...

, 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 that is largely typical of other coastal perciform 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 radials, nostrils located laterally on each side of the head, the lack of a

swim bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled Organ (anatomy), organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their curren ...

, and the presence of multiple

lateral lines Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...

. 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 incl ...

deposits in tissues and reduced ossification 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 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 and metabolic compensation in enzymatic activity. Many notothenoids have lost the nearly universal

heat shock response The heat shock response (HSR) is a cell stress response that increases the number of molecular chaperones to combat the negative effects on proteins caused by stressors such as increased temperatures, oxidative stress, and heavy metals. In a n ...

(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 hemoglobin (or other oxygen-binding and oxygen-transporting pigments) in their blood, the notothenioids of the family Channichthyidae do not express any globin 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 n ...

''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, 1862 ** Genus '' Bovichtus'' Valenciennes, 1832 ** Genus '' Cottoperca''

Steindachner Franz Steindachner (11 November 1834 in Vienna – 10 December 1919 in Vienna) was an Austrian zoologist, ichthyologist, and herpetologist. He published over 200 papers on fishes and over 50 papers on reptiles and amphibians. Steindachner describ ...

, 1875 ** Genus '' Halaphritis'' Last, Balushkin & Hutchins, 2002 * Family Pseudaphritidae McCulloch, 1929 ** Genus '' Pseudaphritis'' Castelnau, 1872 * Family Eleginopsidae Gill, 1893 ** Genus '' Eleginops'' Gill, 1862 * Family Nototheniidae Günther, 1861 ** Genus ''

Aethotaxis The longfin icedevil (''Aethotaxis mitopteryx''), also known as the threadfin pinhead, is a species of marine ray-finned fish belonging to the family Nototheniidae, the notothens or cod icefishes. It is native to the Southern Ocean where it can b ...

'' H. H. DeWitt, 1962 ** Genus '' Cryothenia'' Daniels, 1981 ** Genus '' Dissostichus'' Smitt, 1898 ** Genus ''

Gobionotothen ''Gobionotothen'' is a genus of marine ray-finned fishes belonging to the family Nototheniidae, the notothens or cod icefishes. They are native to the Southern Ocean. Taxonomy ''Gobionotothen'' was first formally described in 1976 by the Russian ...

'' Balushkin, 1976 ** Genus ''

Gvozdarus ''Gvozdarus'' is a genus of marine ray-finned fishes belonging to the family Nototheniidae, the notothens or cod icefishes. It is native to the Southern Ocean. Taxonomy ''Gvozdarus'' was first formally described as a genus in 1989 by the Soviet ...

'' Balushkin, 1989 ** Genus ''

Lepidonotothen The grey rockcod (''Lepidonotothen squamifrons''), also known as the grey notothen, stripe-eyes notothen or stripe-eyed rockcod, is a species of marine ray-finned fish belonging to the family Nototheniidae, the notothens or cod icefishes. It is n ...

'' Balushkin, 1976 ** Genus ''

Lindbergichthys ''Lindbergichthys'' is a genus of marine ray-finned fishes belonging to the family Nototheniidae, the notothens or cod icefishes. Froese, R. and D. Pauly. Editors. (2021). FishBase. Lindbergichthys Balushkin, 1979. Accessed through: World Reg ...

'' Balushkin, 1979 ** Genus '' Notothenia''

Richardson Richardson may refer to: People * Richardson (surname), an English and Scottish surname * Richardson Gang, a London crime gang in the 1960s * Richardson Dilworth, Mayor of Philadelphia (1956-1962) Places Australia *Richardson, Australian Capi ...

, 1844 ** Genus ''

Nototheniops ''Nototheniops'' is a genus of marine ray-finned fishes belonging to the family Nototheniidae, the notothens or cod icefishes. The species in this genus are native to the Southern Ocean. Taxonomy ''Nototheniops'' Was first formally described as ...

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

Patagonotothen ''Patagonotothen'' is a genus of marine ray-finned fishes, belonging to the family Nototheniidae, the notothens or cod icefishes. They are native to the southeast Pacific Ocean, southern Atlantic Ocean and the Southern Ocean. Taxonomy ''Patagono ...

'' Balushkin, 1976 ** Genus '' Pleuragramma'' Balushkin, 1982 ** Genus '' Trematomus''

Boulenger Boulenger is a surname. Notable people with the surname include: * Benjamin Boulenger (born 1990), French footballer * Edward George Boulenger (1888–1946), British zoologist, director of aquarium at London Zoo * George Albert Boulenger (1858–1 ...

, 1902 * Family Harpagiferidae Gill, 1861 ** Genus ''

Harpagifer ''Harpagifer'', the spiny plunderfishes is a genus of marine ray-finned fishes, belonging to the family Harpagiferidae, it is the only genus in this monotypic family. They are found in the Southern Ocean. Taxonomy The genus ''Harpagifer'' was de ...

'' Richardson, 1844 * Family Artedidraconidae Andriashev, 1967 ** Genus '' Artedidraco'' Lönnberg, 1905 ** Genus '' Dolloidraco'' Roule, 1913 ** Genus '' Histiodraco''

Regan The family name Regan, along with its cognates O'Regan, O Regan, Reagan, and O'Reagan, is an Anglicized form of the Irish surname Ó Riagáin or Ó Ríogáin, from Ua Riagáin. The meaning is likely to have originated in ancient Gaelic ''ri' ...

, 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 ''Gerlachea'' is a monotypic genus of marine ray-finned fish belonging to the family Bathydraconidae, the Antarctic dragonfishes, its only species is ''Gerlachea australis''. It is found at depths of from over the Antarctic continental shelf. T ...

'' Dollo, 1900 ** Genus '' Gymnodraco'' Boulenger, 1902 ** Genus '' Parachaenichthys'' Boulenger, 1902 ** Genus ''

Prionodraco ''Prionodraco'' is a monotypic genus of marine ray-finned fish belonging to the family Bathydraconidae, the Antarctic dragonfishes, its only species is ''Prionodraco evansii''. These fishes are native to the Southern Ocean. Taxonomy ''Prionodra ...

'' Regan, 1914 (one species) ** Genus '' Psilodraco'' Norman. 1937 ** Genus '' Racovitzia'' Dollo, 1900 ** Genus ''

Vomeridens ''Vomeridens'' is a monotypic genus of marine ray-finned fish belonging to the family Bathydraconidae, the Antarctic dragonfishes, its only species is ''Vomeridens infuscipinnis''. These fishes are native to the Southern Ocean. Taxonomy ''Vomer ...

'' DeWitt & Hureau, 1980 * Family Channichthyidae Gill, 1861 ** Genus '' Chaenocephalus'' Richardson, 1844 ** Genus '' Chaenodraco'' 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'' Nybelin, 1947 ** Genus '' Pagetopsis'' Regan, 1913 ** Genus '' Pseudochaenichthys'' Norman, 1937