Takifugu

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This article is about the genus of pufferfish Takifugu; for the Japanese dish, see fugu.

Fugu
File:Fugu in Tank.jpg
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Actinopterygii
Order: Tetraodontiformes
Family: Tetraodontidae
Genus: Takifugu
Abe, 1949
Species

See species table below

Takifugu is a genus of pufferfish, often better known by the Japanese name fugu (Japanese: 河豚, literally "river pig"). There are 25 species belonging to the genus Takifugu, which can be found worldwide from about 45° latitude north to 45° latitude south, mostly in salt water, but sometimes also in fresh water or brackish water. Their diet consists mostly of algae, mollusks, 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.

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

There are 25 species belonging to the genus Takifugu (formerly known as Fugu, with the exception of one remaining Fugu species). Takifugu can be found worldwide from about 45° latitude north to 45° latitude south, mostly in salt water near coral reefs or the shore, but some species also live in fresh water or brackish water. Their diet consists mostly of algae, mollusks, invertebrates and sometimes crustaceans. All fishes in the tetradon family have strong teeth that may grow too long if the fish cannot consume abrasive food. Fugu can bite if provoked. Not all species are studied in detail, but the most researched takifugu is Takifugu rubripes, due to the commercial consumption and breeding of the fish. Takifugu rubripes, for example, breeds from March to May and lays eggs attached to rocks at a depth of around 20m. 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.

Takifugu rubripes serves as a model organism in biological research.[1]

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).

Previously, it was unknown how pufferfish inflation took place. Recently, however, Dr. Peter Wainwright completed his analysis on the series of muscle actions which allow a pufferfish to inflate. 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. Depending on the species the fugu can achieve an almost perfect spherical shape.

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 [2]. 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 30 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 (Takifugu rubripes and Tetraodon nigroviridis).

Takifugu species table

Species of the Genus Takifugu
Species Author Common Name Distribution Max. Size Comments
Takifugu alboplumbeus Richardson, 1845 Komon-damashi (Japan) West Pacific 23cm Poisonous, Salt Water
Takifugu basilevskianus? Basilewsky Darkgreen Puffer, Sansaifugu (Japan) ? ? Poisonous
Takifugu bimaculatus Richardson, 1845 Futatsuboshi-fugu (Japan) Northwest Pacific 30cm Poisonous
Takifugu chinensis* Abe, 1949 Eyespot Puffer, Karasu (Japan) Northwest Pacific 55cm Poisonous
Takifugu coronoidus* Ni & Li, 1992 暈環多紀魨 (China) Northwest Pacific ? Not poisonous
Takifugu chrysops* Hilgendorf, 1879 Red-eyed Puffer, Akamefugu (Japan) Northwest Pacific 20cm Poisonous
Takifugu exascurus Jordan & Snyder, 1901 Mushifugu (Japan) Northwest Pacific 15cm Poisonous
Takifugu flavidus Li, Wang & Wang, 1975 Towny Puffer, Sansaifugu (Japan), Hwang-jom-pok (Korea), Jú húng dong fang tún (China) Northwest Pacific 35cm Poisonous
Takifugu niphobles* Jordan & Snyder, 1901 Grass Puffer, Starry puffer, Kusafugu (Japan), Cá Nóc sao (Viet Nam) Northwest Pacific 15cm Poisonous
Takifugu oblongus Bloch, 1786) Oblong blow fish, Lattice blaasop (India), Bebo (India) Buntal (Malaysia), Pita-pita (Indonesia), Ruitjies-blaasop (South Africa) West Pacific 40cm Not Poisonous
Takifugu obscurus* Abe, 1949 Obscure Puffer, Mefugu (Japan) Western Pacific 40cm Poisonous
Takifugu ocellatus Linnaeus, 1758 Ocellated Puffer Asia ? Not Poisonous
Fugu orbimaculatus Kuang, Li & 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 Pacific 30cm Poisonous
Takifugu poecilonotus* Temminck & Schlegel, 1850 Fine Patterned Puffer, Komonfugu (Japan), Huin-jom-pok (Korea), Ban dian dong fang tún (China) Northwest Pacific 20cm Poisonous
Takifugu porphyreus* Temminck & Schlegel, 1850 Purple Puffer, Namera-fugu (Japan), Mafugu (Japan), Kom-pok (Korea), Zi sè dong fang tún) (China) Northwest Pacific 52cm Poisonous
Takifugu pseudommus Chu, 1935 Nameradafugu (Japan), Nameradamashi (Japan) Northwest Pacific 35cm Poisonous
Takifugu radiatus Abe, 1947 Nashifugu (Japan) Northwest Pacific 20cm Poisonous
Takifugu reticularis Tien, Chen & Wang, 1975 Reticulate Puffer, Amime-fugu (Japan) Northwest Pacific 29cm Poisonous
Takifugu rubripes* Temminck & Schlegel, 1850 Torafugu (Japan), Tiger Puffer, Hóng qí dong fang tún (China), Cha-ju-pok (Korea) Northwest Pacific 70cm Poisonous, Used in Chinese Medicine, Genome sequenced completely
Takifugu snyderi* Abe, 1988 Shosai-fugu (Japan) Western Pacific 30cm Poisonous
Takifugu stictonotus* Temminck & Schlegel, 1850 Spotback, Spottyback Puffer, Gomafugu (Japan) Northwest Pacific 35cm Poisonous
Takifugu vermicularis Temminck&Schlegel, 1850 Pear Puffer, Shosaifugu (Japan),, Nashifugu (Japan), Kuk-mae-ri-bok (Korea), Chóng wén dong fang tún (China) Northwest Pacific 30cm Poisonous
Takifugu xanthopterus* Temminck & Schlegel, 1850 Yellowfin puffer, Shimafugu (Japan), Kka-ch'i-pok (Korea), Tiáo wén dong fang tún (China) Northwest Pacific 50cm Poisonous

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

See also

References

  1. Yves Van de Peer (2004). "Tetraodon genome confirms Takifugu findings: most fish are ancient polyploids". Genome Biology. 5 (250): 250. doi:10.1186/gb-2004-5-12-250.
  2. Usio Simidu et al., (1987). "Marine Bacteria Which Produce Tetrodotoxin". AEM. 53: 1714–5.

External links

nl:Takifugu zh-yue:雞泡魚


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