White-spotted Puffer, Arothron hispidus
|Scientific classification |
The pufferfish, also called blowfish, swellfish, 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. 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 pear-shaped pufferfish is a slow swimmer, and mainly uses its small pectoral 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, Cone Snails, 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, 8μg tetrodotoxin per kg 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.
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).
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).
Puffy the pufferfish has been chosen as the mascot of the OpenBSD project.
- Fugu sequencing project (http://fugu.hgmp.mrc.ac.uk/PFW/)
- Tetraodon sequencing project (http://www.broad.mit.edu/annotation/tetraodon/index.html)
- EMedicine Article about the Toxicity of Tetrodotoxin (http://www.emedicine.com/emerg/topic576.htm)
- Half Japanese half English page with Information about the species and their toxicity (http://www.coara.or.jp/~sueyoshi/data03/fugu00.html)
- Extensive List of all Genus and Species for the family Tetraodontidae (http://f15.aaacafe.ne.jp/~ichthy/hugu/hugu2ka.html)
- FishBase listing for Tetraodontidae (http://www.fishbase.org/identification/specieslist.cfm?famcode=448&areacode=)