''Dissostichus'', the toothfish, is a genus of marine

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

belonging to the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Nototheniidae, the notothens or cod icefish. These fish are found in the Southern Hemisphere. Toothfish are marketed for consumption in the United States as Chilean sea bass (or Chilean seabass) or less frequently as white cod. "Chilean sea bass" is a marketing name coined in 1977 by Lee Lantz, a fish wholesaler who wanted a more attractive name for selling the Patagonian toothfish to Americans. Retrieved on 16 May 2015.G. Bruce Knecht, ''Hooked: Pirates, Poaching, And the Perfect Fish", 2006. . p. 9'' In 1994, the U.S.

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...

(FDA) accepted "Chilean sea bass" as an "alternative market name" for Patagonian toothfish. The toothfish was remarkably successful in the United States, Europe and Asia, and earned the nickname "white gold" within the market. Toothfish are vital to the ecological structure of

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 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is the seco ...

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

s. For this reason, on 4 September a national day is dedicated to the toothfish in

South Georgia South Georgia is an island in the Atlantic Ocean, South Atlantic Ocean that is part of the British Overseas Territories, British Overseas Territory of South Georgia and the South Sandwich Islands. It lies around east of the Falkland Islands. ...

Taxonomy

''Dissostichus'' was first described as a genus in 1898 by the Swedish

zoologist Zoology ( , ) is the scientific study of animals. Its studies include the structure, embryology, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. Zoology is one ...

Fredrik Adam Smitt, he was describing a new species from waters off

Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South America, South American mainland, across the Strait of Magellan. The archipelago consists of the main is ...

, ''Dissostichus eleginoides'', which he placed as the only species in the new genus. Some authorities place this

taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

in the

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...

Pleuragrammatinae, but the 5th edition of ''

Fishes of the World ''Fishes of the World'' is a standard reference for the systematics of fishes. It was first written in 1976 by the American ichthyologist Joseph S. Nelson (1937–2011). Now in its fifth edition (2016), the work is a comprehensive overview of t ...

'' does not include subfamilies in the Nototheniidae. The name of the genus ''Dissostichus'' is a compound of ''dissos'' which means "twofold" or "double" and ''stichus'' which means "row" or "line", an allusion to the two

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelia ...

s of ''D. eleginoides''.

Species

Two species in this genus are recognized: *'' Dissostichus eleginoides'' Smitt, 1898 (Patagonian toothfish) *'' Dissostichus mawsoni'' Norman, 1937 (Antarctic toothfish)

Distribution

The Patagonian toothfish is distributed circumpolarly near the

Antarctic Convergence The Antarctic Convergence or Antarctic Polar Front is a marine belt encircling Antarctica, varying in latitude seasonally, where cold, northward-flowing Antarctic waters meet the relatively warmer waters of the sub-Antarctic. The line separate ...

, spanning the

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

and Indian sectors of the Southern Ocean, with a few populations near the

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martin in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctica. ...

as well as the coasts of

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

and

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. The Antarctic toothfish is distributed around the

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...

and in the

Ross Sea The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, and is the southernmost sea on Earth. It derives its name from the British explorer James Clark Ross who ...

, generally south of 60°S. Both species are benthopelagic as adults. The Patagonian toothfish has been found at depths between 600 and 1500 m, and the Antarctic toothfish tends to be found at depths between 1300 and 1900 m. The Patagonian and Antarctic toothfish populations overlap geographically in the southern Indian Ocean, north of the

and several south Atlantic islands.Roberts, J.; et al. (2011). "The diet of toothfish species" ''Dissostichus eleginoides'' and ''Dissostichus mawsoni'' with overlapping distributions. ''J. Fish Bio.'' 79, 138–154. Since the Southern Ocean has not yet been fully sampled, both species may extend further throughout the region.Collins M.A., et al. (2010). "The Patagonian toothfish: biology, ecology and fishery". ''Adv. Mar. Bio.'' 58, 227–300.

Morphology and body size

The Patagonian toothfish and the Antarctic toothfish are markedly similar in appearance, but can be identified via several morphological features. The Patagonian toothfish has a characteristic scaleless patch between the eyes and a longer visible

. Both species are long-lived and relatively slow-growing. The Patagonian toothfish can live up to at least 50 years of age and the Antarctic toothfish can live to at least 35 years of age.Horn P.L. (2002). "Age and growth of Patagonian toothfish (''Dissostichus eleginoides'') and Antarctic toothfish (''D. mawsoni'') in waters from the New Zealand subantarctic to the Ross Sea, Antarctica". ''Fish. Res.''56, 275–287. Both species show the fastest growth in the first 10 years of life, and reach maximum body size around 20 years of age. The Patagonian toothfish grows at an average rate of 2 cm and 1 kg per year. Toothfishes are large in size, with both species reaching maximum sizes exceeding 100 kg. This trait distinguishes the toothfishes from other notothenioids.

History

The Patagonian toothfish was initially captured in the 1970s as

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

via trawl fishing vessels around

South Georgia Island South Georgia is an island in the Atlantic Ocean, South Atlantic Ocean that is part of the British Overseas Territories, British Overseas Territory of South Georgia and the South Sandwich Islands. It lies around east of the Falkland Islands. ...

and off the coast of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. Most of the individuals caught using this method were juveniles.Constable A.J. et al. (2000). Managing fisheries to conserve the Antarctic marine ecosystem: practical implementation of the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR). ''J. Mar. Sci.'' 57, 778-791. In 1987, the Patagonian toothfish was caught as bycatch via

longline fishing Longline fishing, or longlining, is a commercial fishing angling technique that uses a long ''main line'' with baited hooks attached at intervals via short branch lines called ''snoods'' or ''gangions''. The fish, marketed as "Chilean Sea Bass," became widely successful in restaurants due to its large size and white, oily flesh, which can be cooked in numerous ways. Fish were collected in massive numbers, first in

and later in

after the Chilean population declined abruptly in 1994. Exploratory fisheries for the Antarctic toothfish were established in the Ross Sea in 1996/1997. The fisheries for the two toothfish species are intended to be distinct; however, there is some concern that the species may be indistinguishable to commercial fishermen. In 2013, the FDA eliminated market distinctions between the species, meaning that the Antarctic toothfish, like its congener, could also be marketed as Chilean Sea Bass. Previously, the Antarctic toothfish was sold under the name "toothfish."

Commercial fisheries

All

fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life or, more commonly, the site where such enterprise takes place ( a.k.a., fishing grounds). Commercial fisheries include wild fisheries and fish farm ...

south of the Antarctic Convergence are regulated by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which is a subset of the international

Antarctic Treaty System The Antarctic Treaty and related agreements, collectively known as the Antarctic Treaty System (ATS), regulate international relations with respect to Antarctica, Earth's only continent without a native human population. It was the first arms ...

designed to prevent exploitation of the region’s natural resources. CCAMLR currently oversees thirteen licensed toothfish fisheries, including seven exploratory fisheries and one research fishery.Ccamlr.org. Toothfish fisheries. Accessed 29 January 2019. The five established fisheries target the Patagonian toothfish exclusively, and the exploratory fisheries, mostly concentrated in the

, target the Antarctic toothfish primarily. The research fishery targets both species. The Patagonian toothfish, which has been caught and sold since 1977, is currently being removed legally from the Southern Ocean at an estimated rate of 12,000 to 17,000 tons per year. The Antarctic toothfish, which has been caught and sold since 1988, is currently being removed legally from the Southern Ocean at an estimated rate of 4,000 tons per year. All known Antarctic toothfish and most Patagonian toothfish populations fall within the CCAMLR Convention Area.Lack M. and Sant G. (2001). Patagonian toothfish: Are conservation and trade measures working? ''TRAFFIC Bul.''19, 1-18. Northern Patagonian toothfish populations are managed by the nations that control the respective regions in which the populations reside; however, these nations are required to adhere to CCAMLR regulations.

Illegal, unreported and unregulated fishing

As of 2014, CCAMLR was allowing fisheries to remove the Antarctic toothfish at rates that would reduce the population to 50 percent of its current biomass. However, some scientists are concerned that estimations of toothfish biomass may be inaccurate due to a number of factors, including illegal, unreported and unregulated (IUU) fishing activities.Abrams, P.A. (2014). How precautionary is the policy governing the Ross Sea Antarctic toothfish (''Dissostichus mawsoni'') fishery? ''Antarc. Sci.'' 26, 3-13. IUU activities can be challenging to prevent and prove. However, centralized international collaborative efforts (between

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

, the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

and

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

) to mitigate IUU activities have been reported as successful. As of 2012, measures included CCAMLR’s catch-documentation scheme along with on-sea, satellite and aerial surveillance. A 2012 report indicated that implementation of these measures has reduced IUU activity by 90 percent. However, in 2014 others stated that these numbers may be inaccurate, as IUU fishing in the Southern Ocean is difficult to prove.

Diet and ecological importance

Both species occupy similar

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of Resource (biology), resources an ...

s. They are

piscivorous A piscivore () is a carnivorous animal that primarily eats fish. Fish were the diet of early tetrapod evolution (via water-bound amphibians during the Devonian period); insectivory came next; then in time, the more terrestrially adapted rept ...

at all life stages. Juveniles mostly prey on small notothenioids,

krill Krill ''(Euphausiids)'' (: krill) are small and exclusively marine crustaceans of the order (biology), order Euphausiacea, found in all of the world's oceans. The name "krill" comes from the Norwegian language, Norwegian word ', meaning "small ...

squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...

and

pelagic fish Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs. ...

es. Prey range increases with maturity. As adults, both species consume a variety of fishes,

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s and

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s. The Patagonian toothfish is

opportunistic 300px, ''Opportunity Seized, Opportunity Missed'', engraving by Theodoor Galle, 1605 Opportunism is the practice of taking advantage of circumstances — with little regard for principles or with what the consequences are for others. Opport ...

, and sometimes scavenges

penguin Penguins are a group of aquatic flightless birds from the family Spheniscidae () of the order Sphenisciformes (). They live almost exclusively in the Southern Hemisphere. Only one species, the Galápagos penguin, is equatorial, with a sm ...

and fish remains that sink from the epipelagic zone. The toothfishes may compete with

Adélie penguin The Adélie penguin (''Pygoscelis adeliae'') is a species of penguin common along the entire coast of the Antarctic continent, which is the only place where it is found. It is the most widespread penguin species, and, along with the emperor peng ...

s for prey such as

silverfish The silverfish (''Lepisma saccharinum'') is a species of small, primitive, wingless insect in the order Zygentoma (formerly Thysanura). Its common name derives from the insect's silvery light grey colour, combined with the fish-like appearanc ...

and krill. Toothfish are important prey for large mammals. Patagonian toothfish predators include elephant seals,

sperm whale The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the Genus (biology), genus ''Physeter'' and one of three extant species in the s ...

s, and

killer whale The orca (''Orcinus orca''), or killer whale, is a toothed whale and the largest member of the oceanic dolphin family. The only extant species in the genus '' Orcinus'', it is recognizable by its black-and-white-patterned body. A cosmopolit ...

s. Antarctic toothfish predators include

Weddell seal The Weddell seal (''Leptonychotes weddellii'') is a relatively large and abundant Earless seal, true seal with a Subantarctic, circumpolar distribution surrounding Antarctica. The Weddell seal was discovered and named in the 1820s during expediti ...

s and whales, especially killer whales. Some data suggests that the

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing Fish stocks, fish stock), resu ...

of toothfish may stress whale populations. Hucke-Gaete et al. observed that when toothfish were removed from via longline capture, killer whales were more likely to prey on nearby sperm whales.

Migration and reproductive cycle

Much remains unknown regarding the life cycles of both toothfish species, particularly the Antarctic toothfish. Much of the existing data has been collected by reports from commercial fishing vessels. Current research suggests that both the Patagonian and Antarctic toothfishes tend to form discontinuous populations, meaning that little

gene flow In population genetics, gene flow (also known as migration and allele flow) is the transfer of genetic variation, genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent ...

exists between populations. Both species migrate during

spawning Spawn is the Egg cell, eggs and Spermatozoa, sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of freely releasing eggs and sperm into a body of water (fresh or marine); the physical act is ...

season. However, the specific duration and distance of these migrations have not been fully characterized. Tag-and-release experiments on the Patagonian toothfish have indicated that most individuals migrate an average of 15 miles from their habitat, and that any migratory movement generally occurs after the fishes reach maturity. However, some anecdotal evidence demonstrates that the Patagonian toothfish may be capable of migrating between the northern and southern poles, likely by submerging beneath tropical and temperate waters.

Patagonian toothfish

The Patagonian toothfish spawns in deep waters during the austral winter and early spring, between June and September. Discontinuous

oogenesis Oogenesis () or ovogenesis is the differentiation of the ovum (egg cell) into a cell competent to further develop when fertilized. It is developed from the primary oocyte by maturation. Oogenesis is initiated before birth during embryonic devel ...

development patterns suggest that Patagonian toothfish do not spawn annually. Individuals migrate to spawn in shallower waters (800–1000 m), although migration patterns can vary widely between different geographic populations. Some data suggest that spawning yields decrease at higher latitudes. Egg development occurs over a period of approximately three months, with hatching occurring in October or November. After hatching, the

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic larvae drift for a period of time, likely until February. Around this time, the fish reach a critical size and become

bathypelagic The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above and the abyssopelagic below. The bathypela ...

. They gradually inhabit deeper waters as they grow, migrating down the

continental slope A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margi ...

. Adult fish are generally found at depths greater than 500 m.

Antarctic toothfish

The life cycle of the Antarctic toothfish is less well-characterized. Researchers and fisheries are limited to collecting this species during the austral summer and autumn (December to May) due to harsh polar conditions during the austral winter (June to August). Scientists have not yet collected any juvenile or

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

Antarctic toothfishYoung, P. (2012). The last ocean: The toothfish and the battle for Antarctica’s soul''.'' ''Fisheye Films.'' Documentary. and have not yet verified the location, season or frequency of spawning activity. Hanchet et al. used all previously collected data from 1996 to 2008 to generate an updated model for the life cycle of the Antarctic toothfish within the Ross Sea fishery, although the authors note that much of this model is based on speculation and much of the data has not yet been collected fully.Hanchet S.M. et al. (2008). A hypothetical life cycle for Antarctic toothfish (''Dissostichus mawsoni'') in the Ross Sea region. ''CCAMLR Sci''. 15, 35-53. They estimated that the Antarctic toothfish adults spawn between June and November, and that spawning likely occurs north of 70°S, beyond the Ross continental shelf and slope. Eggs likely have a development period of four to five months and hatch between November and February, developing more slowly than their Patagonian toothfish counterparts. Current data suggests that spawning requires a large amount of reproductive tissue, and may not occur annually.

Planktonic Plankton are the diverse collection of organisms that drift in water (or air) but are unable to actively propel themselves against currents (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they pro ...

larvae undergo larval drift for a period of several months, likely into late summer or early autumn. Researchers predict that the Antarctic toothfish inhabit

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

regions after reaching 15 cm. Sub-adult individuals develop within the Ross Sea and gradually inhabit deeper waters over a period of two to three years.

Conservation efforts

In June 2010, 500 scientists formed the Antarctic and Southern Ocean Coalition (ASOC), advocating to CCAMLR for special protection of the entire Ross Sea. Chilean Sea Bass has been placed on the Red Lists of

Greenpeace International Greenpeace is an independent global campaigning network, founded in Canada in 1971 by a group of environmental activists. Greenpeace states its goal is to "ensure the ability of the Earth to nurture life in all its diversity" and focuses its ...

and the One World One Ocean Campaign. As a result, a number of restaurant and grocery owners have publicly opted not to prepare or sell Chilean Sea Bass. Furthermore, advocacy projects have been undertaken to increase the scope of public awareness. The New Zealand documentary ''The Last Ocean'' was created to communicate the issue of toothfish fisheries, conveying the need to protect the Southern Ocean’s native

biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...

. In October 2016, a 1.55 million km² region of the Ross Sea was designated as a

marine protected area A marine protected area (MPA) is a protected area of the world's seas, oceans, estuaries or in the US, the Great Lakes. These marine areas can come in many forms ranging from wildlife refuges to research facilities. MPAs restrict human activity ...

by the CCAMLR, meaning that most fishing is banned in the area. The area will remain protected until 2052.

References

* {{Authority control Nototheniidae Illegal, unreported and unregulated fishing