Takifugu

Takifugu is a genus of pufferfish, often better known by the Japanese name fugu (河豚, lit. "river pig"). There are 25 species belonging to the genus Takifugu and most of these are native to salt and brackish waters of the northwest Pacific, but a few species are found in freshwater of Asia or more widely in the Indo-Pacific region. Their diet consists mostly of algae, molluscs, invertebrates and sometimes crustaceans. The fish defend themselves by inflating their bodies to several times normal size and by poisoning their predators. These defenses allow the fish to actively explore their environment without much fear of being attacked.

This article is about the genus of pufferfish Takifugu. For the Japanese dish, see fugu. For the genus of pufferfish that draws sand-circles, see Torquigener.

Takifugu
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Tetraodontiformes
Family: Tetraodontidae
Subfamily: Tetraodontinae
Genus: Takifugu
T. Abe, 1949
Species

25, See species table below

Synonyms

Gastrophysus Müller, 1843[1]
Fugu T. Abe, 1952

The fish is highly toxic, but despite this—or perhaps because of it—it is considered a delicacy in Japan. The fish contains lethal amounts of the poison tetrodotoxin in the internal organs, especially the liver and the ovaries, but also in the skin and the testes. Therefore, only specially licensed chefs can prepare and sell fugu to the public, and the consumption of the liver and ovaries is forbidden. But because small amounts of the poison give a special desired sensation on the tongue, these parts are considered the most delicious by some gourmets. Every year a number of people die because they underestimate the amount of poison in the consumed fish parts.

The poison paralyzes the muscles while the victim stays fully conscious, and eventually dies from asphyxiation. There is currently no antidote, and the standard medical approach is to try to support the respiratory and circulatory system until the effect of the poison wears off.

The fish is also featured prominently in Japanese art and culture.

Distribution and conservation status

There are 25 species belonging to the genus Takifugu. Most species are restricted to salt and brackish waters of the northwest Pacific, but a few occur more widely in the Indo-Pacific region or in freshwater of Asia. Although several are euryhaline (can adapt to various salinities) to some extent, most are unable to live in freshwater. An exception is the anadromous Takifugu obscurus, which lives in coastal marine waters but migrates into fresh water to spawn in rivers.[2]

Most species in the genus are not considered threatened, but there are two notable exceptions: the critically endangered Takifugu chinensis and the endangered Takifugu plagiocellatus.[3][4]

Takifugu rubripes serves as a model organism in biological research.[5]

Morphology and behaviour

The pear-shaped Takifugu, like all pufferfish, are not fast swimmers as they mainly use their pectoral fins for propulsion, but they are very manoeuvrable and able to hover, swim backwards, and change direction much more quickly than most other types of fish. As a result, they are rarely found in open water and prefer to stay relatively close to the sea bed where they can explore complex environments such as oyster beds, seagrass meadows, and rocky reefs. Nevertheless, these fish are very curious and active, and in some cases even aggressive against other fugu or other fish.

In the event of danger, the fish inflates itself by filling its extremely elastic stomach with water (or air when outside of the water) until the fish is almost spherical (hence the name blowfish or pufferfish). A series of things happen when a pufferfish inflates: First, the pufferfish fills its mouth with water. Then, it seals its mouth using a special valve at the bottom of the mouth. This valve flaps upward and covers the entire mouth of the fish. Next, a branchiostegal ray (a modified gill arch) pushes the water down the esophagus into the stomach. The extremely elastic stomach then expands.[6] Depending on the species the fugu can achieve an almost perfect spherical shape.

Their diet consists mostly of algae, mollusks, invertebrates and sometimes crustaceans. All fishes in the pufferfish family have strong teeth that may grow too long if the fish cannot consume abrasive food. Fugu can bite if provoked. Not all Takifugu have been studied in detail, but the most researched species is Takifugu rubripes, due to the commercial farming of this fish for human consumption. Takifugu rubripes, for example, breeds from March to May and lays eggs attached to rocks at a depth of around 20 m (66 ft). As far as known, most species live exclusively in marine and brackish water, also breeding in this habitat. The anadromous Takifugu obscurus migrates from its coastal marine habitat into fresh water to spawn.[2] An even more exceptional and unique breeding behavior is displayed by Takifugu niphobles. They gather in groups at certain beaches, throw themselves onto land where fertilization happens and then return to the water.[7][8] The eggs either float back into the water or may stay on land under rocks for a period, only hatching when again submerged by high tide.[9] This breeding behavior is unique among pufferfish, but found in a few other unrelated fish like capelin and grunion.[10]

Fugu can also change color over time, and they get a darker or lighter color. This helps them to camouflage. A very dark color may be a sign of stress or illness.

Toxicity

The fish's main defense, however, is the neurotoxin contained in its internal organs, mainly the ovaries and the liver, to a lesser extent in the intestines and the skin, and only minute amounts in the muscles and blood. This makes the fugu a lethal meal for most predators, including the occasional human.

The toxin is called tetrodotoxin, or more precisely anhydrotetrodotoxin 4-epitetrodotoxin and is about 1200 times deadlier than cyanide. This poison can also be found in other animals such as the Blue-Ringed Octopus, cone snails, and even some newts. The pufferfish does not create the poison itself; rather it is generated by bacteria e.g. Pseudomonas within the fish.[11] The fish obtains the bacteria by eating food containing these bacteria. Pufferfish that are born and grown in captivity do not produce tetrodotoxin until they receive some of the poison-producing bacteria, often by eating tissues from a toxin-producing fish. Also, some fish are more poisonous than others. Each fish has enough poison to kill around thirty adult humans.

Genome

Apparently due to some unknown selection pressure, intronic and extragenic sequences have been drastically reduced within this family. As a result, they have the smallest-known genomes yet found amongst the vertebrate animals, while containing a genetic repertoire very similar to other fishes and thus comparable to vertebrates generally. Since these genomes are relatively compact it is relatively fast and inexpensive to compile their complete sequences, as has been done for two species of pufferfishes (Takifugu rubripes and Tetraodon nigroviridis).

Species

The genus Takifugu can be referred to by its lesser synonym Fugu.[12] There are currently 25 recognized species in this genus:[13]

Species of the genus Takifugu
Image Species Author Common name Distribution Max. size Comments
Takifugu alboplumbeusJ. Richardson, 1845 Komon-damashi (Japan)West Pacific23 centimetres (9.1 in) SL Poisonous, Salt Water
Takifugu bimaculatusJ. Richardson, 1845 Futatsuboshi-fugu (Japan)Northwest Pacific30 centimetres (12 in) SL Poisonous
Takifugu chinensis*T. Abe, 1949 Eyespot Puffer, Karasu (Japan)Northwest Pacific55 centimetres (22 in) SL Poisonous
Takifugu chrysops*Hilgendorf, 1879 Red-eyed Puffer, Akamefugu (Japan) Northwest Pacific20 centimetres (7.9 in) SLPoisonous
Takifugu coronoidus Y. Ni & C. S. Li, 1992暈環多紀魨 (China) Northwest Pacific?Not poisonous?
Takifugu exascurusD. S. Jordan & Snyder, 1901 Mushifugu (Japan)Northwest Pacific15 centimetres (5.9 in) SL Poisonous
Takifugu flavidusC. S. Li?, C. X. Wang & Y. G. Wang?, 1975 Yellowbelly pufferfish, Towny puffer, Sansaifugu (Japan), Hwang-jom-pok (Korea), Jú húng dong fang tún (China) Northwest Pacific35 centimetres (14 in) SLPoisonous
Takifugu niphobles*D. S. Jordan & Snyder, 1901 Grass Puffer, Starry puffer, Kusafugu (Japan), Cá Nóc sao (Viet Nam) Northwest Pacific15 centimetres (5.9 in) TLPoisonous
Takifugu oblongusBloch, 1786 Oblong blow fish, Lattice blaasop (India), Bebo (India) Buntal (Malaysia), Pita-pita (Indonesia), Ruitjies-blaasop (South Africa) West Pacific40 centimetres (16 in) TLPoisonous
Takifugu obscurus*T. Abe, 1949 Obscure Puffer, Mefugu (Japan)Western Pacific40 centimetres (16 in) SL Poisonous
Takifugu ocellatus Linnaeus, 1758 Ocellated PufferAsia15 centimetres (5.9 in) TLPoisonous
Takifugu orbimaculatusY. D. Kuang, C. S. Li & S. H. Liang, 1984 圓斑多紀魨 (China)Asia?Not Poisonous?
Takifugu pardalis* Temminck & Schlegel, 1850 Panther puffer, Higanfugu (Japan), Chol-pok (Korea), Bào wén dong fang tún (China) Northwest Pacific30 centimetres (12 in) SLPoisonous
Takifugu plagiocellatus C. S. Li, 2002 Northwest Pacific, China10.9 centimetres (4.3 in) SL
Takifugu poecilonotus* Temminck & Schlegel, 1850 Fine Patterned Puffer, Komonfugu (Japan), Huin-jom-pok (Korea), Ban dian dong fang tún（斑点东方鲀） (China) Northwest Pacific20 centimetres (7.9 in) SLPoisonous
Takifugu porphyreus*Temminck & Schlegel, 1850 Purple Puffer, Namera-fugu (Japan), Mafugu (Japan), Kom-pok (Korea), Zi sè dong fang tún) (China) Northwest Pacific52 centimetres (20 in) TLPoisonous
Takifugu pseudommusY. T. Chu, 1935 Nameradafugu (Japan), Nameradamashi (Japan) Northwest Pacific35 centimetres (14 in) SLPoisonous
Takifugu radiatusT. Abe, 1947 Nashifugu (Japan)Northwest Pacific20 centimetres (7.9 in) SL Poisonous
Takifugu reticularisM. C. Tian, Q. T. Cheng & Q. Wang, 1975 Reticulate Puffer, Amime-fugu (Japan) Northwest Pacific29 centimetres (11 in) SLPoisonous
Takifugu rubripes*Temminck & Schlegel, 1850 Torafugu (Japan), Japanese Puffer, Tiger Puffer, Hóng qí dong fang tún（红鳍东方鲀） (China), Cha-ju-pok (Korea) Northwest Pacific80 centimetres (31 in) TL Poisonous, Used in Chinese Medicine, Genome sequenced completely
Takifugu snyderi*T. Abe, 1988 Shosai-fugu (Japan)Western Pacific30 centimetres (12 in) SL Poisonous
Takifugu stictonotus* Temminck & Schlegel, 1850 Spotback, Spottyback Puffer, Gomafugu (Japan) Northwest Pacific35 centimetres (14 in) SLPoisonous
Takifugu variomaculatus C. S. Li & Y. D. Kuang, 2002 Northwest Pacific, China13.7 centimetres (5.4 in) SL
Takifugu vermicularisTemminck & Schlegel, 1850 Purple Puffer, Pear Puffer, Shosaifugu (Japan), Nashifugu (Japan), Kuk-mae-ri-bok (Korea), Chóng wén dong fang tún (China) Northwest Pacific30 centimetres (12 in) SLPoisonous
Takifugu xanthopterus* Temminck & Schlegel, 1850 Yellowfin puffer, Shimafugu (Japan), Kka-ch'i-pok (Korea), Tiáo wén dong fang tún (China) Northwest Pacific50 centimetres (20 in) SLPoisonous

* Fish that have edible body parts according to the Japanese Ministry of Health and Welfare

See also

References
  1. Kottelat, M. (2013). The Fishes of the Inland Waters of Southeast Asia: A Catalogue and Core Bibliography of the Fishes Known to Occur in Freshwaters, Mangroves and Estuaries. The Raffles Bulletin of Zoology, 2013, Supplement No. 27: 1–663.
  2. Kato, A.; H. Doi, T. Nakada, H. Sakai and S. Hirose (2005). Takifugu obscurus is a euryhaline fugu species very close to Takifugu rubripes and suitable for studying osmoregulation. BMC Physiology 5: 18. doi:10.1186/1472-6793-5-18.
  3. Shao, K.; Leis, J.L.; Hardy, G.; Jing, L.; Liu, M. & Pollard, D. (2014). "Takifugu chinensis". The IUCN Red List of Threatened Species. IUCN. 2014: e.T193605A2246312. doi:10.2305/IUCN.UK.2014-3.RLTS.T193605A2246312.en.
  4. Shao, K.; Liu, M.; Hardy, G.; Jing, L.; Leis, J.L. & Matsuura, K. (2014). "Takifugu plagiocellatus". The IUCN Red List of Threatened Species. IUCN. 2014: e.T193654A2254725. doi:10.2305/IUCN.UK.2014-3.RLTS.T193654A2254725.en.
  5. Van de Peer, Yves (2004). "Tetraodon genome confirms Takifugu findings: most fish are ancient polyploids". Genome Biology. 5 (250): 250. doi:10.1186/gb-2004-5-12-250. PMC 545788. PMID 15575976.
  6. Wainwright, P.C.; and R.G. Turingan (1997). Evolution of Pufferfish Inflation Behavior. Evolution 51(2): 506–518. doi:10.2307/2411123
  7. Motohashi, E.; T. Yoshihara; H. Doi; and H. Ando (2010). Aggregating Behavior of the Grass Puffer, Takifugu niphobles, Observed in Aquarium During the Spawning Period. Zoological Science 27(7): 559–564. doi:10.2108/zsj.27.559
  8. Yamahira, K. (1997). Proximate factors influencing spawning site specificity of the puffer fish Takifugu niphobles. Marine Ecology Progress Series 147: 11–19.
  9. Martin, K.L.; A.L. Carter (2013). "Brave New Propagules: Terrestrial Embryos in Anamniotic Eggs". Integrative and Comparative Biology. 53 (2): 233–247. doi:10.1093/icb/ict018. PMID 23604618.
  10. Martin, K.L.M. (2014). Beach-Spawning Fishes: Reproduction in an Endangered Ecosystem. CRC Press. ISBN 978-1482207972.
  11. Usio Simidu; et al. (1 July 1987). "Marine Bacteria Which Produce Tetrodotoxin". AEM. ASM. 53 (7): 1714–5. doi:10.1128/AEM.53.7.1714-1715.1987. PMC 203940. PMID 3310884.
  12. Matsuura, Keiichi (1990). "The pufferfish genus Fugu Abe, 1952, a junior subjective synonym of Takifugu Abe, 1949". Bull. Natn. Sci. Mus., Tokyo, Ser. A. 16: 15–20.
  13. Froese, Rainer and Pauly, Daniel, eds. (2012). Species of Takifugu in FishBase. October 2012 version.
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