One defensive adaptation pufferfish have developed is the ability to ingest large quantities of air or water into their elastic stomachs until they expand themselves into almost spherical shapes. Since puffers also have sharp spines, they are almost inedible when inflated. If predators manage to swallow them, most puffers have the further adaptation of one of the most lethal neurotoxins in the world.
Though pufferfish have good eyesight and the ability to move each eye independently, they are clumsy and slow. When unable to escape pursuit, pufferfish employ the backup defense of their ability to inflate. Their toxicity is due to the presence of tetrodotoxin in their liver, ovaries, intestines and skin. Some species of fish such as sharks and lizardfish seem immune to the poison and eat pufferfish, but to humans, tetrodotoxin is 1,200 times as lethal as cyanide. One pufferfish carries enough poison to kill 30 humans and no antidote exists.