A viperfish is any species of marine fish in the genus 'Chauliodus'. Viperfish are characterized by long, needle-like teeth and hinged lower jaws. A typical viperfish grows to lengths of 30 to 60 cm (12 to 23.5 in).

Viperfish stay near lower depths (250–5,000 feet [80–1,520 m]) in the daytime and shallower depths at night, primarily in tropical and temperate waters.

Viperfish are believed to attack prey after luring them within range with light-producing organs called 'photophores', which are located along the ventral sides of its body, and with a prominent 'photophore' at the end of a long spine in the dorsal fin.

The viperfish flashes this natural light on and off, at the same time moving its dorsal spine around like a fishing rod and hanging completely still in the water. It also uses the light producing organ to communicate to potential mates and rivals.

Viperfish vary in color from green, silver, to black. A viperfish uses its fang-like teeth to immobilize prey and would not be able to close its mouth because of their length, if it were not able to fold and curve them behind its head.

The first vertebra behind the head of the viperfish absorbs the shock of biting prey. As with other deepsea fish, they are able to undergo long periods with scarcely any food.

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