Extract from the July issue of PFK:
"What about the poison?
Puffers possess a quality that makes them undesirable for predators - poisonous flesh. High concentrations of tetradotoxin (about 1200 times deadlier than cyanide) are found in the organs of marine puffers, namely the liver, ovaries, intestines and skin, while freshwater puffers have a similar poison, saxitoxin, found mainly in the skin.
The toxin results from bacteria present in their natural diet, nd ouffers that do not have access to their natural diet tend to be less poisonous, if at all.
Puffer flesh, known as fugu, is a delicacy in Japan. Specially trained chefs prepare the meat for consumption. However, sometimes chefs will prepare the meat so it contains minute traces of poison. This causes a tingling of the lips and slight euphoria. Despite stringent precautions, humans have died after eating puffer flesh.
I think I'll keep my puffers as pets and stick to cod or haddock. And before you ask, this poison is not a danger if you are only keeping puffers in aquaria."