Puffer fish are members of the family Tetraodontidae who are also commonly called blowfish. Both of their monikers are references to their astounding inflation skills -- a convenient technique for protecting themselves against outside threats. These saltwater fish are robust, and because of that are usually suitable for aquarium life.
Puffing up in puffer fish is no joke. When puffer fish feel they're in hazardous situations, they rapidly increase the size of their physiques by taking in a lot of water, or sometimes air. In doing this, puffer fish often put their intimidating pointy prickles on full display, although not all varieties have them. Not only are these prickles extremely painful, they are often poisonous, too, both to animals and people. This puffing, plain and simple, serves as a serious "back off now" sign to any threats to these fish. If a puffer fish ever looks like a ball, he feels unsafe and frightened, so take note and be extremely cautious.
What Exactly Happens
Puffer fish have notably flexible and springy bellies, and when they quickly take in lots of H20, it causes them immediately to look a lot bigger and puffier than normal. When puffer fish puff up, they usually look several times bigger than they do when they are in "normal," peaceful and calm moods.
When puffer fish seemingly out of nowhere become massive in front of their predators, it often deters them from even trying to get closer, as it's not at all an easy task to swallow these guys. The spines don't exactly look too comfortable or enticing, either. Many puffer fish predators simply give up and exit the situation, looking elsewhere for a more cooperative meal. If an especially persistent predator attempts to sink his teeth into the puffer fish regardless, however, he could encounter a bad experience, to the tune of an aggressive and paralyzing poison. Although not all puffer fish are equipped with this strong poison, many are. The poison is called tetrodotoxin, and it not only has an awful taste, it can be life-threatening.
Puffer fish are naturally rather sluggish and bumbling creatures, far from swift and graceful swimmers. Since this makes them highly susceptible to attack by predators, puffing up is a handy protective mechanism. They can't flee their attackers easily, but they sure can scare them away.