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

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...

belonging to the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Nototheniidae, the notothens or cod icefish. These fish are found in the Southern Hemisphere. Toothfish are marketed 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 federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...

(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 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-smal ...

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

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

South Georgia South Georgia ( es, Isla San Pedro) is an island in the South Atlantic Ocean that is part of the British Overseas Territory of South Georgia and the South Sandwich Islands. It lies around east of the Falkland Islands. Stretching in the east� ...

Taxonomy

''Dissostichus'' was first described as a genus in 1898 by the Swedish zoologist Fredrik Adam Smitt, he was describing a new species from waters off

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

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

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus Genus ( plural genera ) is a taxonomic rank used in the biological classifica ...

Pleuragrammatinae, but the 5th edition of ''

Fishes of the World ''Fishes of the World'' by the American ichthyologist Joseph S. Nelson (1937–2011) is a standard reference for fish systematics. Now in its fifth edition (2016), the work is a comprehensive overview of the diversity and classification of the ...

'' 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 epithelial ...

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. Antarctic waters pr ...

, spanning the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

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 definition, to Antarctica) in the south, and is bounded by the contine ...

and

Indian Indian or Indians may refer to: Peoples South Asia * Indian people, people of Indian nationality, or people who have an Indian ancestor ** Non-resident Indian, a citizen of India who has temporarily emigrated to another country * South Asia ...

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 Martín 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 Antarctic ...

as well as the coasts of

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

and

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...

. The Antarctic toothfish is distributed around the

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and othe ...

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 island ...

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 between 600 and 1500 m, and the Antarctic toothfish tends to be found 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. The Southern Ocean has not yet been fully sampled, so 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 ( es, Isla San Pedro) is an island in the South Atlantic Ocean that is part of the British Overseas Territory of South Georgia and the South Sandwich Islands. It lies around east of the Falkland Islands. Stretching in the east� ...

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 relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

. 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 ground). Commercial fisheries include wild fisheries and fish farms, ...

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 russian: link=no, Договор об Антарктике es, link=no, Tratado Antártico , name = Antarctic Treaty System , image = Flag of the Antarctic Treaty.svgborder , image_width = 180px , caption ...

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 Ross Sea, 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 sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

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 coun ...

, 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 Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...

and

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

) 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 resources and competitors (for ...

s. They are piscivorous at all life stages. Juveniles mostly prey on small notothenioids,

krill Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word ', meaning "small fry of fish", which is also often attributed to species of fish. Krill are consi ...

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fittin ...

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 do live on or near the bottom, and reef fish that are associated with coral re ...

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

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

s and

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

s. The Patagonian toothfish is opportunistic, and sometimes scavenges penguin 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 pen ...

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 appearance ...

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 ''Physeter'' and one of three extant species in the sperm whale famil ...

s, and

killer whale The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus ''Orcinus'' and is recognizable by its black-and-white pat ...

s. Antarctic toothfish predators include Weddell seals and whales, especially killer whales. Some data suggests that the overfishing 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 gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...

exists between populations. Both species migrate during spawning 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, ovogenesis, or oögenesis 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 in the embryonic stage. ...

development patterns suggest that Patagonian toothfish do not

spawn Spawn or spawning may refer to: * Spawn (biology), the eggs and sperm of aquatic animals Arts, entertainment, and media * Spawn (character), a fictional character in the comic series of the same name and in the associated franchise ** '' Spawn: A ...

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 found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...

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 bathypelagi ...

. 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 margin ...

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

marine protected area Marine protected areas (MPA) are protected areas of 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 for a con ...

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

References

* {{Taxonbar, from=Q2369129 Nototheniidae Illegal, unreported and unregulated fishing