PUFFERFISH

There are many beautiful types of this prolific reef resident, but pufferfish harbour a dangerous secret. Although we may be aware of it's protective mechanism - expanding into an enormous ball if threatened - we are less aware that they also contain one of nature's most dangerous poisons, tetrodotoxin.

This naturally occurring toxin is derived from the scientific name for pufferfish (order tetraodontidae, meaning four toothed) and was once assumed to be a metabolic product of the fish. However, recent research now points to the production of tetrodotoxin by several relatively common bacterial species that are eaten by reef animals. Although they become immune to it, the puffers accrue the toxin in their internal organs and skin.

Tetrodotoxin is extremely potent and acts by shutting down the nervous system. The amount found in one puffer is enough to kill over 30 people. The victim is usually fully aware of it’s actions as the poison cannot pass the blood-brain barrier, but turns the peripheral nervous system off. Death is via asphyxiation. Funny then, that many South East Asian nations regard eating puffer fish as a delicacy - fugu - despite the risks it entails.

DEFENCE - Puffer fish are gentle creatures that only use their defence mechanism if attacked by a predator. Then they deploy a special valve in their mouths to suck water into a pleated stomach, expanding up to 3 times their normal size.

Dive guides used to think it was a good game to find a puffer and harrass it enough for it to do this. Actually, this is not a game - try to discourage anyone you see doing it.

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