Tetraodontidae

Tetraodontidae

Tetraodontidae is a family of primarily marine and estuarine fish. The family includes many familiar species which are variously called puffers, balloonfish, blowfish, bubblefish, globefish, swellfish, toadfish, and toadies. They are morphologically similar to the closely related porcupinefish, which have large conspicuous spines (unlike the small, almost sandpaper-like spines of Tetraodontidae). The scientific name, Tetraodontidae, refers to the four large teeth, fused into an upper and lower plate, which are used for crushing the shells of crustaceans and mollusks, and red worms, their natural prey.

Puffer Fish are the second most poisonous vertebrate in the world, the first being a Golden Poison Frog. The skin and certain internal organs of many Tetraodontidae are highly toxic to humans, but nevertheless the meat of some species is considered a delicacy in both Japan (as fugu) and Korea (as bok-uh). If one is caught while fishing, it is recommended that thick gloves are worn to avoid poisoning and getting bitten when removing the hook.

The Tetraodontidae contains at least 121 species of puffers in 19 genera. They are most diverse in the tropics and relatively uncommon in the temperate zone and completely absent from cold waters. Pufferfish are mostly found in coastal regions though some are oceanic (e.g., Lagocephalus lagocephalus) or live in the deep sea (e.g., Sphoeroides pachygaster). A large number of puffers are found in brackish and fresh waters: at least 39 marine species enter brackish or freshwater to feed or breed (e.g., Arothron hispidus), and a further 28 species are completely freshwater fish in distribution and never enter the sea (e.g., Colomesus asellus).

Distribution

The entire Tetraodontidae family has a worldwide distribution. Its members are found near shore in shallow seas from the Atlantic to the Pacific. Many members of the family can be found in areas of brackish water such as estuaries. Some select species are even known to exist entirely in polluted water.

Ecology and life history

Natural defenses

The puffers's unique and distinctive natural defenses are great due to their particular form of locomotion. Puffers use a combination of pectoral, dorsal, anal, and caudal fins for propulsion that make them highly maneuverable but very slow, and therefore comparatively easy targets for predators. As a defense mechanism, puffers have the ability to inflate rapidly, filling their extremely elastic stomachs with water (or air when outside the water) until they are almost spherical in shape. Thus, a hungry predator stalking the puffers may suddenly find itself facing what seems to be a much larger fish and pause, giving the puffers an opportunity to retreat to safety. When lifted out of water there is a risk that puffers inflate with air. This may result in problems deflating again afterwards. When this happens with aquarium specimens the recommended course of action for fishkeepers is to hold the puffer underwater by the tail, head upwards, and shake the fish gently until the air escapes out of the mouth.

Some puffers also produce a powerful neurotoxin in their internal organs, making them an unpleasant, possibly lethal, meal for any predatory fish that eats one. This neurotoxin is found primarily in the ovaries and liver, although smaller amounts exist in the intestines and skin, as well as trace amounts in muscle tissue and in its blood. Many puffers have bright colors and distinctive markings and make no attempt to hide from predators. This is likely an example of aposematism.

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 fish 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).

Puffers are able to move their eyes independently, and many species can change the color or intensity of their patterns in response to environmental changes. In these respects they are somewhat similar to the terrestrial chameleon.

Puffer's toxin evolved as a response to aquatic predators such as larger fish, rather than for use against humans. Note also, not all puffers are poisonous; Takifugu oblongus, for example, is one of the fugu puffers that is not poisonous. However, it should be noted that puffer's neurotoxin is not necessarily as toxic to other animals as it is to humans, and puffers are eaten routinely by some species of fish, such as lizardfish and tiger sharks

Tetrodotoxin

The puffer's toxin is called tetrodotoxin, or more precisely anhydrotetrodotoxin 4-epitetrodotoxin. It is also found within other animals such as the blue-ringed octopus, cone snail, and in certain varieties of newt. Tetrodotoxin is produced within the puffers by bacteria, which are acquired through food. This means that puffers raised in captivity do not contain tetrodotoxin, and therefore are not poisonous until they come into contact with the bacteria. The puffer itself has immunity to the poison due to a mutation in the protein sequence of the Sodium ion channel on the cell membranes.

Tetrodotoxin is an exceptionally lethal poison. Tetrodotoxin is approximately 1,200 times deadlier than cyanide. In animal studies with mice, 8 μg tetrodotoxin per kilogram of body weight killed 50% of the mice (see also LD50). It is estimated that a single puffer has enough poison to kill 30 adult humans.

Reproduction

The balloonfish has a pelagic, or open-ocean, life stage. Spawning occurs after males slowly push females to the water surface. The eggs are spherical and buoyant, floating in the water. Hatching occurs roughly after four days. The larvae are predominately yellow with scattered red spots. They are well developed with a functional mouth, eyes, and a swim bladder. Larvae less than ten days old are covered with a thin shell. After the first ten days, the shell is lost and the spines begin to develop. The larvae undergo a metamorphosis approximately three weeks after hatching. During this time, all the fins and fin rays are present and the teeth are formed. The red and yellow colors of the larvae do not persist into the juvenile phase and are replaced by the olives and browns; characteristic of adults. Dark spots also appear on the juvenile's underside. Pelagic juveniles are often associated with floating sargassum, and these spots may serve as camouflage from predators such as dolphin that swim below the seaweeds. Juveniles retain spotting until they move inshore and become adults. The juvenile balloonfish does not undergo another metamorphosis to become an adult. All changes now are external and include elongation of the spines and normal body growth.

Human Interaction

Poisoning

Puffer poisoning usually results from consumption of incorrectly prepared puffer soup, chiri or occasionally from raw puffer meat, sashimi fugu. While chiri is much more likely to cause death, sashimi fugu often causes intoxication, light-headedness, and numbness of the lips, and is often eaten for this reason. Puffer's (tetrodotoxin) poisoning will cause deadening of the tongue and lips, dizziness, and vomiting. These are followed by numbness and prickling over the body, rapid heart rate, decreased blood pressure, and muscle paralysis. Death results from suffocation as diaphragm muscles are paralyzed. Patients who live longer than 24 hours are expected to survive, although the poison can cause comas lasting several days. Many people report being fully conscious during the entirety of the coma, and can often remember everything that was said while they were supposedly unconscious. In Voodoo, puffer's poison must be ingested by the victim for the black magic of creating "zombies," most likely because of the pseudocomatose effect.

Pufferfish, called pakpao, are also consumed in Thailand, usually by mistake, at times these fish are eaten because they are cheaper to buy, and there is little awareness or monitoring of the situation. Patients are regularly hospitalized or die as there are no specific preparations to remove the toxin before eating.

Treatment consists of supportive care and intestinal decontamination with gastric lavage and activated 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 puffers. Cases of neurologic symptoms, including numbness and tingling of the lips and mouth, have been reported to arise rapidly after the consumption of puffers caught in the area of Titusville, Florida. These symptoms are generally resolved within hours to days, although one affected individual required intubation for 72 hours. As a result of such cases, Florida banned the harvesting of puffers from certain bodies of water.

Drug development

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.

See also

References

Further reading

  • 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 393170260X.
  • 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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