The pufferfish is a family of fish, with about 100 species. They are also known as the blowfish, fugu, swellfish, and globefish. They are called the pufferfish because when they are threatened, they puff up to about twice their normal size by gulping water. In this enlarged state, the pufferfish can swim at only about half their normal speed. Pufferfish are generally believed to be the second-most poisonous vertebrates in the world, after the golden poison frog. They use tetrodotoxin, a powerful neurotoxin.