Porcupinefish are fish belonging to the family Diodontidae (order Tetraodontiformes), also commonly called blowfish and, sometimes, balloonfish and globefish. They are sometimes collectively called pufferfish, not to be confused with the morphologically similar and closely related Tetraodontidae, which are more commonly given this name.
Porcupinefish are medium- to large-sized fish, and are found in shallow temperate and tropical seas worldwide. A few species are found much further out from shore, wherein large schools of thousands of individuals can occur. They are generally slow.
Porcupinefish have the ability to inflate their bodies by swallowing water or air, thereby becoming rounder. This increase in size (almost double vertically) reduces the range of potential predators to those with much bigger mouths. A second defense mechanism is provided by the sharp spines, which radiate outwards when the fish is inflated.
(extract from Wikipedia)