Marine pufferfish generally contain a large amount of tetrodotoxin (TTX) in 
their skin and viscera, and have caused many incidences of food poisoning, 
especially in Japan. Edible species and body tissues of pufferfish, as well as 
their allowable fishing areas, are therefore clearly stipulated in Japan, but 
still 2 to 3 people die every year due to pufferfish poisoning. TTX is 
originally produced by marine bacteria, and pufferfish are intoxicated through 
the food chain that starts with the bacteria. Pufferfish become nontoxic when 
fed TTX-free diets in a closed environment in which there is no possible 
invasion of TTX-bearing organisms. On the other hand, TTX poisoning due to 
marine snails has recently spread through Japan, China, Taiwan, and Europe. In 
addition, TTX poisoning of dogs due to the ingestion of sea slugs was recently 
reported in New Zealand. TTX in these gastropods also seems to be exogenous; 
carnivorous large snails are intoxicated by eating toxic starfish, and 
necrophagous small-to-medium snails, the viscera of dead pufferfish after 
spawning. Close attention must be paid to the geographic expansion and/or 
diversification of TTX-bearing organisms, and to the sudden occurrence of other 
forms of TTX poisoning due to their ingestion.