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Tetraodontidae

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Pufferfish
White-spotted Puffer, Arothron hispidus
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Subphylum:
Vertebrata
Class:
Actinopterygii
Order:
Tetraodontiformes
Family:
Tetraodontidae
Genera

Amblyrhynchotes
Arothron
Auriglobus
Canthigaster
Carinotetraodon
Chelonodon
Colomesus
Contusus
Ephippion
Feroxodon
Fugu
Gastrophysus
Javichthys
Lagocephalus
Liosaccus
Marilyna
Monotretus
Omegaphora
Pelagocephalus
Polyspina
Reicheltia
Sphoeroides
Takifugu
Tetractenos
Tetraodon
Torquigener
Tylerius
Xenopterus
For species see text

The 'pufferfish', also called blowfish, swellfish, globefish, balloonfish are fish making up the family Tetraodontidae, within the order Tetraodontiformes. They are named for their ability to inflate themselves to several times their normal size by swallowing water or air when threatened; the same adaptation is found in the closely related porcupinefish, which also have spines (unlike pufferfish).

The eyes and internal organs of most pufferfish are highly toxic, but nevertheless its meat is considered a delicacy in Japan and Korea. The name "fugu" is used both for the fish that are eaten and for their meat (for more details see Fugu).

There are 185 known species of the family Tetraodontidae, of which 38 can be found in Japan. They 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.

The pufferfish is a relatively slow swimmer, and depending on the species it mainly uses combinations of its pectoral, dorsal, anal, and caudal fins for propulsion, which does not allow it to escape predators very well. In case of danger, they inflate themselves by filling their extremely elastic stomach with water (or air when outside the water) until they are almost spherical. In case this defense fails, pufferfish also contain a powerful neurotoxin in their internal organs, making them a lethal meal for most predators. It is found mainly in the ovaries and liver, to a lesser extent in the intestines and skin, and only in small amounts in the muscles and blood.

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, or even some newts. The pufferfish does not create the poison itself; rather it is generated by various genera of bacteria within the fish. 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. A poisonous fish has enough poison to kill 30 adults.

Tetrodotoxin is a very potent neurotoxin and shuts down electrical signaling in nerves by binding to the pores of sodium channel proteins in nerve cell membranes. It does not cross the blood-brain barrier, leaving the victim fully conscious while paralyzing the remainder of the body. In animal studies with mice, 8 µg tetrodotoxin per kilogram of body weight killed 50% of the mice. The pufferfish itself has immunity to the poison due to a mutation in the protein sequence of the sodium channel pump on the cell membranes.

Tetrodotoxin is one of the deadliest natural toxins and is not destroyed by washing, cooking, or other food preparation. It concentrates in the liver and visceral organs of the pufferfish and is also found in several species of frogs, salamanders, and octopus.

Tetrodotoxin binds sodium channels, preventing sodium influx into nerve axons. It also acts on vascular smooth muscle and skeletal muscle. Symptoms of tetrodotoxin occur rapidly after ingestion and include weakness, dizziness, paresthesias of the face and extremities, nausea, and loss of reflexes. With higher doses there is severe hypotension and, in some cases, general paralysis. Death can occur due to respiratory failure and hypotension. It is not unusual for the patient to remain conscious while paralyzed.

Treatment of pufferfish poisoning consists of supportive care and intestinal decontamination with gut lavage and charcoal. Case reports suggest that anticholinesterases such as edrophonium may be effective.

Saxitoxin, the cause of PSP (Paralytic shellfish poisoning, red tide), can also be found in pufferfish. Cases of neurologic symptoms, including numbness and tingling of the lips and mouth, have been reported to arise rapidly after the consumption of pufferfish caught in the area of Titusville, Florida. These symptoms generally resolve within hours to days, although one affected individual required intubation for 72 hours. As a result of such cases, Florida banned the harvesting of pufferfish from certain bodies of water.

A drug called Tectin™ that is derived from tetrodotoxin is being developed as a potent pain reliever. Administered in very small quantities it can bring relief to those suffering from intense chronic pain, such as that experienced by some cancer patients. Other uses, such as helping opiate addicts through withdrawal, are also being studied.

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).

Black-spotted Puffer (Arothron nigropunctatus)

Pufferfish are also one of few kinds of fish that can blink or close their eyes. (Some claim they are the only fish that can close its eyes, but certain attacking sharks close their eyes to protect themselves from struggling prey).

Species

Trivia

  • Puffy the pufferfish has been chosen as the mascot of the OpenBSD project.
  • Bloat, voiced by Brad Garrett, is a pufferfish in Finding Nemo.
  • Dolphins have been observed using pufferfish as a sort of toy in the wild. They tease the pufferfish with their teeth, causing the small fish to become alarmed and then inflate. After a while the fish calms down and deflates, thus starting the cycle over again. It is speculated that dolphins may also enjoy the mild numbing effect from small amounts of the pufferfish toxin.
  • The covers of the books "Understanding Japanese Information Processing" and "Understanding CJKV Information processing" by Ken Lunde, published by O'Reilly, feature an engraving of a pufferfish.
  • When lifted out of water, pufferfish can inflate with air, but they may have problems deflating again afterwards. When this happens with aquarium specimens, fishkeepers hold the puffer underwater by the tail, head upwards, and shake the fish gently until the air escapes out of the mouth.


who cares

References

Arreola, V.I., and M.W. Westneat. 1996. Mechanics of propulsion by multiple fins: kinematics of aquatic locomotion in the burrfish (Chilomycterus schoepfi). Proceedings of the Royal Society of London B 263: 1689-1696.

Ebert, Klaus (2001): The Puffers of Fresh and Brackish Water, Aqualog, ISBN 3-031702-60-X

Gordon, M.S., Plaut, I., and D. Kim. 1996. How puffers (Teleostei: Tetraodontidae) swim. Journal of Fish Biology 49: 319-328.

Plaut, I. and T. Chen. 2003. How small puffers (Teleostei: Tetraodontidae) swim. Ichthyological Research 50: 149-153.

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