Tetrodotoxin is a potent, water soluble, neurotoxin associated with fish of the family Tetraodontidae, hence the name. Fish in this family are called pufferfish, or go by the Japanese name fugu. There are marked differences in toxicity among species, some species are virtually non-toxic. The toxin is present in various organs of the fish, including the muscle tissues, though concentrations are much higher in the gonads, liver, intestines and skin, than in the muscle. The illness induced by the toxin is tetrodotoxicosis (puffer fish poisoning).