Portunus trituberculatus
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''Portunus trituberculatus'', the ''gazami'' crab, South Korea's blue crab or horse crab, is the most widely fished
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
of
crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all th ...
in the world. It is found off the coasts of
East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea ...
and is closely related to '' Portunus armatus''.


Fishery

''Portunus trituberculatus'' is the world's most heavily fished crab species, with over 300,000 
tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1000  kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s being caught annually, 98% of it off the coast of
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
. This is because it is considered highly nutritious, especially in regard to crab cream (roe).


Distribution

''Portunus trituberculatus'' is found off the coasts of
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
,
Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
Palau Palau,, officially the Republic of Palau and historically ''Belau'', ''Palaos'' or ''Pelew'', is an island country and microstate in the western Pacific. The nation has approximately 340 islands and connects the western chain of the ...
and
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...
.


Description

The
carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...
may reach wide, and from front to back. ''P. trituberculatus'' may be distinguished from the closely related (and also widely fished) ''P. armatus'' by the number of broad teeth on the front of the carapace (three in ''P. trituberculatus'', four in ''P. armatus'') and on the inner margin of the merus (four in ''P. trituberculatus'', three in ''P. armatus'').


Relationship to humans


Controversy

Due to the increased farming scale and breeding of ''Portunus trituberculatus,'' the farming environment of the gazami crab has greatly decayed. It has also diminished the gazami crab's immune system which has led to the decline in its ability to fight off diseases. This can be observed by looking at the tooth-paste disease along with the emulsification disease that is caused by vibrio. These two diseases have caused a great deal of damage to ''Portunus trituberculatus'' which has created severe economic losses and deprivation to the industry. These diseases have ultimately reduced the comfort and healthy evolution of the gazami crab's farming industry.


Taxonomy

''Portunus trituberculatus'' was first described by Edward J. Miers in 1876, under the name ''Neptunus trituberculatus''. To better understand the species development, evolution and reproduction a reference genome has been sequenced, assembling to 1.0 Gb in size and anchoring to 50 chromosomes. And demonstrating it diverged from the
Chinese mitten crab The Chinese mitten crab ('; ,  "big sluice crab"), also known as the Shanghai hairy crab (, pinyin, p ''Shànghǎi máoxiè''), is a medium-sized burrowing crab that is named for its furry claws, which resemble mittens. It is native t ...
around 183.5 million years ago.


Virus research

In 2019 it was discovered that gazami crab populations in China are commonly infected with the ''Flavivirus'' Wenzhou shark flavivirus which was previously identified in all tissues of the Pacific spadenose shark, ''Scoliodon macrorhynchos''. While currently unknown if Wenzhou shark flavivirus causes disease in infected shark hosts, this virus moves horizontally between gazami crabs and sharks in ocean ecosystems in a manner similar to other Flavivirus infections such as Dengue virus, which cycle horizontally between arthropod (mosquito) and vertebrate hosts.


References

{{Taxonbar, from=Q1186447 Portunoidea Edible crustaceans Commercial crustaceans Crustaceans described in 1876 Korean seafood Taxa named by Edward J. Miers