Fugu is a type of fish found in Japan that is highly poisonous and can be fatal if not prepared correctly. It is the only species of fish in Japan that is legally allowed to be served as a delicacy. Fugu is a pufferfish, and its organs contain a deadly neurotoxin called tetrodotoxin. The toxin is so powerful that even a small amount can be fatal. Despite the danger, fugu is still a popular dish in Japan, and chefs must be specially trained and licensed to prepare it.