A viperfish is a deepwater fish with a very skinny body and comparatively large head. More than two dozen viperfish species are recognized in the Chauliodus genus. These fish are best known for their ability to lure prey toward them with an organ that produces light. In the deep depths of temperate or tropical waters, sometimes as far down as 5,000 feet (1,500 m), viperfish tempt smaller fish toward their mouths by flashing their light on and off. In addition to being naturally deceptive, the fish can reportedly move up to twice their body length per second.
In general, viperfish have a slim body that can be anywhere from 1 to 2 feet (0.3 to 0.6 m) in length. The light-producing organ is known as a photophore and is typically located in a spot that tempts smaller fish to swim toward the viperfish’s mouth. It is commonly used to lure prey, confuse larger fish, and attract a mate during mating season. Besides the photophore, an identifying feature of this type of fish is its thin but long teeth residing in a hinged jaw. These fish are normally a shade of black, silver, or green.
There are no reports of viperfish being able to survive in captivity in an aquarium for longer than a handful of hours. These fish are sometimes accidentally caught in fishing nets, and there have been some attempts to keep them alive. A typical assumption as to why they do not survive is that they are simply not suited to living in shallow aquarium water for an extended period of time. In the open sea, viperfish are believed to live as long as 40 years if healthy and not successfully preyed upon by sharks, dolphins, or other predators.
Another type of fish that is occasionally called a viperfish but is not always referred to as such is the lesser weever. This fish can sting humans, injecting a venom that causes extreme pain and swelling. The typical treatment for dealing with this sting is to submerge the affected area of the body in the hottest water that can be applied without damaging the area. In extreme cases, the swelling and pain may require medical attention, even surgery, to effectively reduce the swelling and deal with this type of injury. This type of fish is often encountered by ocean swimmers, usually when they disturb the sand, and fishermen in the act of handling their nets.