Tetrodotoxin
The word "tetrodotoxin" is derived from the order of fish, tetraodontidae, which means "four-toothed". The fish got this name because they have 4 very strong teeth that almost fuse together to form a beak-like structure. They use this "beak" to crack shells open to get food, as well as to chew. Among the puffer fish in this order are: the fahaka puffer(Tetraodon fahaka), the Congo puffer(T. miurus), and the giant mbu puffer. (T. mbu)

Thus, the name "tetrodotoxin" means the toxin derived from the four-toothed fish.Tetrodoxin is not isolated to marine animals either. It is also found in a small California salamander, named Taricha. Recently, there is a lot of evidence to suggest that the puffer fish do not actually make tetrodotoxin, but rather this toxin is derived by a pathway encoded by bacteria which are associated with these fish.

Tetrodotoxin is one of the most potent molecules known. Once introduced, it selectively blocks the voltage-sensitive sodium channels of excitable tissues. As a result, tetrodotoxin inhibits or reduces the chances of an action potential to be produced. Tetrodotoxin is complex in structure and contains a imidazole ring. It is likely that this ring is the part of the molecule that lodges in the channel leaving the rest of the molecule blocking its outer mouth.

Recent research, done by David Berkowitz from the US Food and Drug Administration, Rockville, Maryland, USA., and Ilona Kryspin-Sorensen, from Institute of Toxicology, National Food Agency of Denmark Soborg have further stregthened the argument that in fact Tetrodotoxin comes not from the puffer, but rather, bacteria. In thier article, "Trangenic Fish: Safe to Eat", they discuss several proofs. They include:
1. Puffer fish grown in culture do not produce tetrodotoxin until they are fed tissues from a toxin producing fish.

2. The blue-ringed octopus found in Australian waters accummulates tetrodotoxin in a special salivary gland and infuses its prey with toxin by bite. This octopus contains tetrodotoxin-producing bacteria.

3. Xanthid crabs collected from the same waters contain tetrodotoxin and paralytic shellfish toxin.

4. Tetrodotoxin in algae species Jania is produced by a bacteria species Alteromas .

Although if ingested, Tetrodotoxin is potetially fatal, pufferfish is still considered a delicacy in Japan. As a consequence, Japan also has the highest incidence of textrodotoxin poisoning, even though one must be specially licensed to prepare the fish. But those that are daring enough seem to enjoy the fish. (Provided they survive the actual meal)

I have many different pufferfish in my aquariums at home, and I think they are one of the most interesting fish in terms of personality and their almost "E.T.-like" looks. They are entertaining to watch, and even more interesting to learn about.

Structure of Tetrodotoxin
Other sites of interest
Physiology on the net
FDA's Bad Bug Book
Report by CDC about 3 fugu poisonings in California
Structural model of the Tetrodotoxin binding site of Na+ channel
 
Some information about marine puffers
A picture of my puffer; Chewbacca the Fahaka


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