People that keep puffers in tanks, though, feed them lance fish, brine, blood worms, prawns, and oysters. The puffer fish's beak also helps puffers to crush coral when looking for food. Puffer fish have a very unique defense system. When they get alarmed they puff themselves up with air or water, inflating their bodies to twice their normal size and making its spikes stick straight out. Puffers have a special valve connected to the floor of their mouth that they draw water or air through to inflate themselves.
Some people eat puffers, though, Japanese people call it Fugu and consider it a great delicacy.