Chauliodus

A viperfish is any species of the genus Chauliodus, marine fish inhabiting the twilight or mesopelagic zone. Viperfish are at most around 30 cm (12 in), and are characterized by silvery scales, long needle-like teeth and photophores along the ventral side of their body (though other fish of the family Stomiidae often have the latter two traits).

The photophores or light organs allow viperfish to bioluminesce, which likely allows them to camouflage against the 1% of sunlight that reaches to below 200 m (660 ft) depth, an ability known as counter-illumination. They are found all around the world in tropical and temperate oceans, and undergo diel vertical migration to feed.