Takifugu

Takifugu, also known by the Japanese name , is a genus of pufferfish currently with 25 species. Most are native to salt and brackish waters of the northwest Pacific, but a few species are found in freshwater in Asia or more widely in the Indo-Pacific region. Their diet consists mostly of algae, molluscs, invertebrates and sometimes crustaceans.

These fish contain lethal amounts of tetrodotoxin in the internal organs, especially the liver and the ovaries, but also in the skin and the testes. The toxin 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 toxin wears off.

Distribution and conservation status Currently, 25 species are placed in 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 to some extent, most are unable to live in freshwater. Two exceptions are the Takifugu obscurus and Takifugu ocellatus, which live in coastal marine waters but migrate into fresh water to spawn in rivers.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. .

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.

Morphology and behaviour Not all Takifugu species have been studied in detail, but the most researched species, Takifugu rubripes, serves as a model organism in biological research; its availability is due to the commercial farming of this species for human consumption (in Japan and elsewhere). This species breeds from March to May and lays eggs attached to rocks at a depth of around . Species that live exclusively in marine and brackish waters also breed in this habitat; in contrast, as mentioned above, the anadromous Takifugu obscurus migrates from its coastal marine habitat into fresh water to spawn.

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.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. Yamahira, K. (1997). Proximate factors influencing spawning site specificity of the puffer fish Takifugu niphobles. Marine Ecology Progress Series 147: 11–19. 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. This breeding behavior is unique among pufferfish, but found in a few other unrelated fish like capelin and grunion.Martin, K.L.M. (2014). Beach-Spawning Fishes: Reproduction in an Endangered Ecosystem. CRC Press. .

Toxicity The main defense of Takifugu against predators is the tetrodotoxin contained in its internal organs, mainly the ovaries and the liver. This neurotoxin is also present, albeit at a lower level, in the intestines and the skin, and minute amounts can be found in the muscles and the blood. This makes these fish a lethal meal for most predators, including the occasional human.

Tetrodotoxin, or more precisely anhydrotetrodotoxin 4-epitetrodotoxin, is about 1200 times deadlier than cyanide. It can also be found in other animals such as the blue-ringed octopus, cone snails, and even some newts. Takifugu does not synthesize the toxin itself; rather, it is synthesized by symbiotic bacteria (e.g. Pseudomonas), which the fish obtains by eating food containing the bacteria. Hence, Takifugu born and grown in captivity never produce tetrodotoxin until they are exposed to the toxin-producing bacteria, often by eating tissues from a toxin-producing fish. Toxicity varies from one fish to the next, but generally speaking, each fish has enough tetrodotoxin to kill around 30 adult humans.

Genome Apparently, due to some unknown selection pressure, intronic and extragenic sequences have been drastically reduced within the pufferfish family (to which Takifugu belongs). As a result, they have the smallest-known genomes amongst the vertebrate animals. 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 the family, including Takifugu rubripes (which was the second vertebrate in history to have its genome mapped, only after humans).

Species , there are 25 recognized species in the genus Takifugu: + Species of the genus Takifugu Image Species Author Common name Distribution Max. size Comments Takifugu alboplumbeus Richardson, 1845 Komon-damashi (Japan) West Pacific SL Poisonous Takifugu bimaculatus Richardson, 1845 Futatsuboshi-fugu (Japan) Northwest Pacific SL Poisonous Takifugu chinensis* Abe, 1949 Eyespot puffer, Karasu (Japan) Northwest Pacific SL Poisonous Takifugu chrysops* Hilgendorf, 1879 Red-eyed puffer, Akame-fugu (Japan) Northwest Pacific SL Poisonous Takifugu coronoidus Ni & Li, 1992 晕环东方鲀 (mainland China) Northwest Pacific ? Not poisonous? Takifugu exascurus Jordan & Snyder, 1901 Mushi-fugu (Japan) Northwest Pacific SL Poisonous Takifugu flavidus Li, Wang & Wang, 1975 Yellowbelly pufferfish, towny puffer, Sansai-fugu (Japan), 橘黄东方鲀 (mainland China), Hwang-jom-pok (Korea) Northwest Pacific SL Poisonous Takifugu niphobles* Jordan & Snyder, 1901 Grass puffer, starry puffer, Kusafugu (Japan), Cá Nóc sao (Vietnam) Northwest Pacific TL Poisonous Takifugu oblongus Bloch, 1786 Oblong blowfish, lattice blaasop (India), bebo (India), buntal (Malaysia), pita-pita (Indonesia), ruitjies-blaasop (South Africa) West Pacific TL Poisonous Takifugu obscurus* Abe, 1949 Obscure puffer, Mefugu (Japan) Western Pacific SL Poisonous Takifugu ocellatus Linnaeus, 1758 Ocellated puffer, 弓班东方鲀 (mainland China) Asia TL Poisonous Takifugu orbimaculatus Kuang, Li & Liang, 1984 圆斑东方鲀 (mainland China) Asia ? Not Poisonous? Takifugu pardalis* Temminck & Schlegel, 1850 Panther puffer, Higan-fugu (Japan), 豹纹东方鲀 (mainland China), Chol-pok (Korea) Northwest Pacific SL Poisonous Takifugu plagiocellatus Li, 2002 斜斑东方鲀 (mainland China) Northwest Pacific SL Takifugu poecilonotus* Temminck & Schlegel, 1850 Fine-patterned puffer, Komon-fugu (Japan), 斑点东方鲀 (mainland China), Huin-jom-pok (Korea) Northwest Pacific SL Poisonous Takifugu porphyreus* Temminck & Schlegel, 1850 Purple puffer, Namera-fugu, Mafugu (Japan), 紫色东方鲀 (mainland China), Kom-pok (Korea) Northwest Pacific TL Poisonous Takifugu pseudommus Chu, 1935 Namerada-fugu, Namerada-mashi (Japan) Northwest Pacific SL Poisonous Takifugu radiatus Abe, 1947 Nashi-fugu (Japan) Northwest Pacific SL Poisonous Takifugu reticularis Tian, Cheng & Wang, 1975 Reticulate puffer, Amime-fugu (Japan) Northwest Pacific SL Poisonous Takifugu rubripes* Temminck & Schlegel, 1850 Japanese puffer, tiger puffer, Tora-fugu (Japan), 红鳍东方鲀 (mainland China), Cha-ju-pok (Korea) Northwest Pacific TL Poisonous, Takifugu snyderi* Abe, 1988 Shosai-fugu (Japan) Western Pacific SL Poisonous Takifugu stictonotus* Temminck & Schlegel, 1850 Spotback, spottyback puffer, Goma-fugu (Japan) Northwest Pacific SL Poisonous Takifugu variomaculatus Li & Kuang, 2002 花斑东方鲀 (mainland China) Northwest Pacific SL Takifugu vermicularis Temminck & Schlegel, 1850 Purple puffer, pear puffer, Shosai-fugu (Japan), Nashifugu (Japan), 虫纹东方鲀 (mainland China), Kuk-mae-ri-bok (Korea), Northwest Pacific SL Poisonous Takifugu xanthopterus* Temminck & Schlegel, 1850 Yellowfin puffer, Shima-fugu (Japan), 条纹东方鲀 (mainland China), Ka-ch'i-pok (Korea) Northwest Pacific SL Poisonous * Species with edible body parts (according to the Japanese Ministry of Health and Welfare)

Takifugu

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