The Tetraodontiformes are a highly derived order of striped fish, also called the Plectognathi. These are sometimes classified as a suborder of the order Perciformes. Tetraodontiformes are represented by 10 extant families and at least 349 species overall; most are marine and inhabit and around tropical coral reefs, but some species are found in freshwater streams and estuaries. They have no close relatives and are descended from a line of coral species that emerged around 80 million years ago.
They have different odd shapes, all radical deviations from the streamlined body plan typical of most fish. These shapes range from nearly square or triangular (boxfishes), globose (pufferfishes) to laterally compressed (filefishes), and triggerfish. They vary in size, for example the Rudarius excelsus, which is only 2 cm long, to the sunfish, the largest of all bony fish up to 3 m in length and weighing more than 2 tons.
Most members of this order, except for the Balistidae family, are ostraciiform, which means that the body is rigid and incapable of lateral flexion. Because of this, they are slow and rely on their pectoral, dorsal, anal, and caudal fins for propulsion rather than body undulation. However, the movement is usually quite precise; The dorsal and anal fins help to maneuver and stabilize. In most species, all the fins are simple, small, and rounded, except for the pelvic fins which, if present, are fused and buried. Again, in most limbs, the gill plates are covered with skin, the only gill that opens a small slit above the pectoral fin.
The tetraodontiform strategy appears to be defense at the expense of speed, with all species fortified with modified scales in strong plates or spines or with tough, leathery skin (archival fish and ocean sunfish). Another striking defensive attribute found in puffer fish and porcupines is the ability to inflate their bodies to greatly increase their normal diameter; This is accomplished by sucking water into a diverticulum of the stomach. Many species of Tetraodontidae, Triodontidae, and Diodontidae are protected against predation by tetrodotoxin, a powerful neurotoxin concentrated in the internal organs of animals.
