- The name "viperfish" is also sometimes applied to the lesser weever.
A viperfish is a saltwater fish in the genus Chauliodus, with long, needle-like teeth and hinged lower jaws. They grow to lengths of 30 to 60 cm (12 - 24 inches). Viperfish stay near lower depths (250–5,000 feet) in the daytime and shallow at night, primarily in tropical and temperate waters. It is one of the fiercest predators in the deep sea and is believed to attack its prey by luring them with a light-producing organ called a photophore, which is located on the end of its dorsal spine. It 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 between green, silver, and black. It 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 curve them behind its head. The first vertebra behind the head of the viperfish is known to absorb the shock of its attacks which are mainly targeted against dragonfish and other small creatures. They are able to undergo long periods with scarcely any food.
Viperfish are believed to live from 30 to 40 years in the wild, but in captivity they rarely live more than a few hours. Some species of dolphins and sharks are known to prey upon viperfish. Scientists believe they can swim at a speed of two body lengths per second, but this is not yet an official speed.
There are currently nine recognized species in this genus: 
- Chauliodus barbatus Garman, 1899
- Chauliodus danae Regan & Trewavas, 1929 (Dana viperfish)
- Chauliodus dentatus Garman, 1899
- Chauliodus macouni T. H. Bean, 1890 (Pacific viperfish)
- Chauliodus minimus Parin & Novikova, 1974
- Chauliodus pammelas Alcock, 1892
- Chauliodus schmidti Ege, 1948
- Chauliodus sloani Bloch & J. G. Schneider, 1801 (Sloane's viperfish)
- Chauliodus vasnetzovi Novikova, 1972
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