Notothenioidei
Encyclopedia
The Antarctic icefish belong to the perciform suborder Notothenioidei and are the largely endemic
, dominant fish taxa in the cold continental shelf waters surrounding Antarctica. At present, the suborder includes 8 families with 43 genera
and 122 species. Although the Southern Ocean
is relatively well sampled, new species of notothenioids are still being described.
The majority of Notothenioids live at seawater temperatures between of –2°C and 4°C, but some sub-polar species inhabit waters that may be as warm as 10°C around New Zealand
and South America
. It is possible to have seawater temperatures below the freezing point of fresh water (0°C) because dissolved salts lower the freezing point of a solution in a colligative manner. Notothenioids have a depth range of about 1500 metres.
The notothenioids all lack a swimbladder, and the majority of species are therefore benthic or demersal in nature. However, a depth-related diversification has given rise to some species attaining increased buoyancy, using lipid
deposits in tissues and reduced ossification
of bony structures. Reduced ossification of the skeleton in the Notothenioids changes their weight and henceforth has created a sort of neutral balance in the water, where the notothenioid does not sink nor float, and can thus adjust depth easier.
Notothenioids have evolved a variety of interesting 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
. Many Notothenioid fish 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 the Antarctic species do. Some sub-polar 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 haemoglobin (or other oxygen-binding and oxygen-transporting pigments) in their blood, the Notothenioids of the family Channichthyidae
have only 1%. They can still flourish in part because of the high oxygen content of the cold waters of the Southern Ocean and in part because oxygen is absorbed and distributed directly by the plasma. These fish must expend twice as much energy in cardiac output per second than the notothenioids with higher hemoglobin concentration.
The notothenioids are generally considered the only marine fish species flock
.
Comparing the genomes of Notothenioidei, which lack red blood cell
s, to close relatives such as the Antarctic rockcod has revealed genes needed to make these blood cells.
Endemic (ecology)
Endemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...
, dominant fish taxa in the cold continental shelf waters surrounding Antarctica. At present, the suborder includes 8 families with 43 genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
and 122 species. Although the Southern Ocean
Southern Ocean
The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...
is relatively well sampled, new species of notothenioids are still being described.
The majority of Notothenioids live at seawater temperatures between of –2°C and 4°C, but some sub-polar species inhabit waters that may be as warm as 10°C around New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. It is possible to have seawater temperatures below the freezing point of fresh water (0°C) because dissolved salts lower the freezing point of a solution in a colligative manner. Notothenioids have a depth range of about 1500 metres.
The notothenioids all lack a swimbladder, and the majority of species are therefore benthic or demersal in nature. However, a depth-related diversification has given rise to some species attaining increased buoyancy, using lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
deposits in tissues and reduced ossification
Ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...
of bony structures. Reduced ossification of the skeleton in the Notothenioids changes their weight and henceforth has created a sort of neutral balance in the water, where the notothenioid does not sink nor float, and can thus adjust depth easier.
Notothenioids have evolved a variety of interesting 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
Southern Ocean
The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...
. Many Notothenioid fish are able to survive in the freezing, ice-laden waters of the Southern Ocean
Southern Ocean
The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...
because of the presence of an antifreeze glycoprotein
Antifreeze protein
Antifreeze proteins or ice structuring proteins refer to a class of polypeptides produced by certain vertebrates, plants, fungi and bacteria that permit their survival in subzero environments. AFPs bind to small ice crystals to inhibit growth and recrystallization of ice that would otherwise be...
in blood and body fluids. Although many of the Antarctic species have antifreeze proteins in their body fluids, not all of the Antarctic species do. Some sub-polar 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 haemoglobin (or other oxygen-binding and oxygen-transporting pigments) in their blood, the Notothenioids of the family Channichthyidae
Channichthyidae
The crocodile icefish or white-blooded fish are a family of perciform fish found in the cold waters around Antarctica and southern South America. Water temperature can drop below 0°C in the Antarctic sea but stays rather constant. There are sixteen known species of crocodile icefish...
have only 1%. They can still flourish in part because of the high oxygen content of the cold waters of the Southern Ocean and in part because oxygen is absorbed and distributed directly by the plasma. These fish must expend twice as much energy in cardiac output per second than the notothenioids with higher hemoglobin concentration.
The notothenioids are generally considered the only marine fish species flock
Species flock
In evolutionary biology, a species flock is a diverse, primarily monophyletic, group of closely related species in an isolated area.A species flock may arise when a species penetrates a new geographical area and diversifies to occupy a variety of ecological niches; this process is known as...
.
Comparing the genomes of Notothenioidei, which lack red blood cell
Red blood cell
Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...
s, to close relatives such as the Antarctic rockcod has revealed genes needed to make these blood cells.
Classification
This classification follows Eastman and Eakin, 2000.- Family Bovichtidae
- Genus Bovichtus (9 species, 8 non-Antarctic)
- Genus Cottoperca (1 species, non-Antarctic)
- Family Pseudaphritidae
- Genus Pseudaphritis (1 species, non-Antarctic)
- Family EleginopidaeEleginopidaeEleginops maclovinus, commonly known as the Patagonian blenny, Falkland's mullet or rock cod, is a species of icefish found in coastal and estuarine habitats around southernmost South America, ranging as far north as Valparaíso on the Pacific side, and Uruguay on the Atlantic side. It is also found...
- Genus Eleginops (1 species, non-Antarctic)
- Family NototheniidaeNototheniidaeThe cod icefishes or nothothens are the family Nototheniidae of acanthopterygian fishes, containing about 50 species in 13 genera. They are traditionally placed in the perciform assemblage together with their relatives, but like every lineage in the "Perciformes" their actual relationships are not...
- Genus Aethotaxis (1 species)
- Genus Cryothenia (2 species)
- Genus DissostichusDissostichusDissostichus is genus of fish found in southern oceans. Individuals may live for over fifty years, reaching lengths over two metres and weigh over 200 kilograms.The genus contains two species...
(2 species) - Genus Gobionotothen (4 species)
- Genus Gvozdarus (1 species)
- Genus Lepidonotothen (6 species, 1 non-Antarctic)
- Genus NototheniaNototheniaNotothenia is a genus of cod icefishes, ray-finned fish in the family Nototheniidae. They inhabit the cold Southern Ocean and other waters around Antarctica...
(5-7 species, 2-3 non-Antarctic) - Genus PagotheniaPagotheniaPagothenia is a genus of cold-water fish. Members of the genus include the bald notothen, which inhabits the waters of the Southern Ocean....
(2 species) - Genus Paranotothenia (2 species)
- Genus Patagonotothen (14 species, all non-Antantarctic)
- Genus Pleuragramma (1 species)
- Genus Trematomus (11 species)
- Family HarpagiferidaeHarpagiferidaeHarpagiferidae, also known as Spiny Plunderfishes, are a type of living, vertebrata fish. This fish carries an IUCN Red List status of "Not Evaluated".-References:*http://www.discoverlife.org/mp/20q?search=Harpagiferidae*http://www.eol.org/pages/5315...
- Genus Harpagifer (6 species)
- Family ArtedidraconidaeArtedidraconidaeArtedidraconidae is a family of marine perciform fishes comprising four genera. Artedidraconidae are endemic to deep waters off Antarctica. The operculum carries a hook-shaped spine and there are four or five hypurals. Artedidraconidae have 33 to 41 vertebrae...
- Genus Artedidraco (6 species)
- Genus Dollodidraco (1 species)
- Genus Histiodraco (1 species)
- Genus Pogonophryne (22 species)
- Family BathydraconidaeBathydraconidaeThe Antarctic dragonfishes are a family, Bathydraconidae, of deep-sea perciform fishes.They are benthopelagic fishes found in Antarctic waters...
- Genus Acanthodraco (1 species)
- Genus Akarotaxis (1 species)
- Genus Bathydraco (5 species)
- Genus Cygnodraco (1 species)
- Genus Gerlachea (1 species)
- Genus Gymnodraco (1 species)
- Genus Parachaenichthys (2 species)
- Genus Prionodraco (1 species)
- Genus Psilodraco (1 species)
- Genus Racovitzia (1 species)
- Genus Vomeridens (1 species)
- Family ChannichthyidaeChannichthyidaeThe crocodile icefish or white-blooded fish are a family of perciform fish found in the cold waters around Antarctica and southern South America. Water temperature can drop below 0°C in the Antarctic sea but stays rather constant. There are sixteen known species of crocodile icefish...
- Genus Chaenocephalus (1 species)
- Genus Chaenodraco (1 species)
- Genus Champsocephalus (2 species)
- Genus Channichthys (1 species)
- Genus Chionobathyscus (1 species)
- Genus Chionodraco (3 species)
- Genus Cryodraco (1 species)
- Genus Dacodraco (1 species)
- Genus Neopagetopsis (1 species)
- Genus Pagetopsis (2 species)
- Genus Pseudochaenichthys (1 species)
- Genus Brulenthius (1 species)
- Brulenthius communis