Not only can puffer fish puff up like a balloon, they also produce one of the most potent poisons known to man. The next time you see a puffer fish keep your distance, even if it's on a plate.
The Remarkable Puffer
Puffer fish adaptations have evolved over time with two remarkable abilities. First and most visually striking is the ability of the puffer fish to inflate itself to over three times its natural size. The second outstanding ability of the puffer fish is that it produces a deadly poison, tetrodotoxin. The puffer ranks as the second most poisonous vertebrate behind the golden poison frog of Columbia. A single puffer fish contains enough poison to kill several people.
Puffed Like a Balloon
When the puffer fish is faced with a dangerous situation, for example being caught and thrown onto the deck of a fishing boat, puffer fish will suck air or water into its stomach, and grow to three times its original size. This is an adaptation that is meant to intimidate possible predators. There is nothing dangerous about a puffer fish puffing up, it is not preparing to spit out its contents or threatening to attack with some of its poison. The puffing reaction sends signals. To some fish it might be communicating "I'm bigger than you, don't mess with me." To others the puffing reaction might be a warning, much like the bright colors on poisonous frogs, which communicate "don't eat me, I'm poisonous, you'll regret it."
In addition to being able to puff itself up, the more frightening ability of the puffer fish is to produce the poison tetrodotoxin. Tetrodotoxin is an impressive poison, estimated to be 100 times more potent than cyanide. If purified, less than could fit in a dewdrop (25mg) is capable of killing a person. While not the most deadly poison known to man, that prize is held by botulinum which is used in very small doses for botox, the tetrodoxin in puffer fish will kill the majority of predators that might swallow it. In several countries, most notably Japan, puffers have been documented to claim human lives, mostly due to improper preparation of puffer soup, and sometimes improper preparation of puffer sashimi. The poison is contained mainly in the ovaries and the liver of the puffer fish. Since the poison only is released when the puffer fish is dead, chefs will prepare puffer fish while they are still alive.
The Last Laugh
These two elaborate defenses are the result of the slow and bumbling nature of the puffer fish. The puffer fish has high maneuverability, but low speeds, as it scours the ocean bottom for mulloscs. It has large powerful jaws to break the hard shells of clams and other shelled creatures. Its slow speed and awkward shape leave it a sitting duck for predators. To counter these predators the puffer inflates like a balloon, and if that and all else fails, the puffer gets the last laugh by killing the consumer with potent poison.