It's well known that pufferfish are poisonous - but why are they? Rupert Collins enlightens us.

Most puffers harbour a neurotoxin called tetrodotoxin (TTX) which if ingested causes paralysis and death among humans. It is concentrated in the liver, ovaries and skin of the fish, but the flesh of the Fugu puffer (Takifugu rubripes) is an expensive delicacy in Japan.

The toxin is accumulated through the food chain. Marine bacteria initially create the TTX which builds up through grazing and scavenging invertebrates such as starfish and snails.

Ancestors of today’s pufferfish evolved resistance, enabling them to feed on these poisonous sources.

Once immunity was acquired, they stored and utilised the poison as a defence against predators.

Puffers raised in captivity and fed no TTX-containing foods are safe to eat.

This article was first published in the December 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.