Viperfish

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.

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.

Although it may look like it is covered in scales, it in fact is covered by a thick, transparent coating of unknown substance Extremely large, fang-like teeth gives the fish a slightly protruded lower jaw which makes catching prey easy for this deep-sea predator. The viperfish is lined with three different types of photophores which some speculate is used to lure in unsuspecting prey They have microscopic spheres without a pigment layer that are scattered over the dorsal side, large spheres with a pigment coat, reflectors, and lens, and finally, large, bell-shaped organs with a pigment coat, reflectors, and lens that are grouped together in rows along the dorsal surface. Photophores can also be seen along the ventral and lateral surface of the fish 

Habitat

Because viperfish live in bathypelagic environments inaccessible to humans, very little is known about their habits. They are found from a depth of 1000 to 4000 meters with an average temperature of 4 degrees Celsius. Viperfish are thought to engage in a daily vertical migration, as they have been observed in the mesopelagic region during the night, which lies directly above the bathypelagic region. More direct observation is needed to confirm this assumption, however.

Feeding

Viperfish do not appear to have any preferred prey: stomach contents of captured individuals have contained lanternfish,bristlemouthes, and other fish, suggesting that they attack and swallow whatever random prey they encounter. With their dark coloration, they can appear invisible and have been observed to remain motionless for hours ready to strike on unsuspecting prey Prey is captured and killed by being pierced by the viperfish's long teeth as the prey is grasped in the viperfish's mouth: subdued prey is then swallowed whole. The photophores along the viperfish's belly are thought to help lure prey closer to it, though further observation is need to confirm this hypothesis.