The common names of the approximately 250 species known to date in this group, which contains four to six families, reveal their fierce, predaceous nature. Besides the various dragonfish—the name that is often used for the entire order—there are viperfish, hatchetfish, snaggletooths and loosejaws, but many of these species have no common names because they are uncommon, even rare. These fish live in mid- to deep waters and thus are rarely encountered by mariners, fishermen or others who would award them a common name. That’s fortunate, as a chance meeting with a dragonfish and a subsequent attack on a diver’s feet or a fisherman’s hands could certainly prove painful if not life-changing. How much of a human could be swallowed by a 20-inch (50 cm) fish is uncertain, but surely enough to do a lot of damage. On the rare occasions when dragonfish have been seen, they had been contorted by the drastic pressure change as they were pulled to the surface dead.
The mysterious dragonfish, which have long bodies and tend to be dark in coloring, are not high-profile predators like the shark or the giant squid, but they well deserve the few common names they’ve been awarded. Although dragonfish don’t breathe fire, they have numerous flashing photophores to attract or illuminate prey, confuse potential predators and communicate with other members of their species. Dragonfish eat anything and everything, even feeding on animals larger than themselves. This feat is accomplished through a combination of hinged teeth and specialized jaws that can expand dramatically.
Hatchetfish, part of one branch of the order, actually have small teeth and appear to feed mainly on plankton. They undertake vertical migrations, rising with the dimming light of evening to feed in shallower waters and returning to the deep during the day. But their low-key existence is more the exception within the order. The most common and best-known dragonfish are the classic big-toothed predators of fish, squid, crustaceans and anything within striking range. They remain at depth, waiting for the hatchetfish and other migrators to return from a night of feeding, then devour the equivalent of a hearty room-service breakfast in bed.
Dragonfish teeth look like shards of glass. In some species, the lower teeth actually extend up and over the head itself. In other species, the lower teeth fit into deep channels that run from the roof of the mouth into the head along either side of the brain. The teeth don’t get in the way. They have evolved to grab and lock on securely to prey. They are also designed so that the fish can fully open its mouth to acquire prey larger than itself. Once the prey is in the mouth, the internal skeleton of the pectoral fins can be lowered, enabling the prey to pass into the gullet. The stomach is extremely muscular and can expand as needed. In some species of loosejaws, there is no bottom to the mouth. To manage a big-fish meal, a column of muscle with tissue between the lower jaw and gill basket contracts when the prey is safely inside, closing the mouth.
Dragonfish try to avoid predation themselves through black stomach walls that keep the photophores of their prey safely hidden during digestion. They also remain at depth, where most predators either cannot see them or are confused by the dragonfish’s own photophores.