Fish
Viperfish
Chauliodus sloani · also called viperfish, Sloane's viperfish
The viperfish has teeth too big for its own head — needle fangs that curve back nearly to its eyes when the jaws shut, forming a cage no prey escapes. It hangs motionless in the black deep sea, dangling a glowing lure over its head, and its neck is built like a crumple zone to survive the force of its own strike.
Overview
Viperfish live in the deep ocean worldwide, at around 250 to 1,500 metres by day, rising at night to feed. About 30 cm long, dark and slender with an enormous hinged jaw and fangs that do not fit its mouth, they ambush small fish and crustaceans.
A lure on its back
The elongated first dorsal fin ray ends in a glowing photophore the fish dangles over its own head to draw prey within range.
Bracing for its own strike
The first vertebra behind the head is a flexible shock absorber that soaks up the impact of the fish’s high-speed lunge.
Status
The viperfish is Least Concern, widespread through the world’s deep oceans and not targeted by fisheries.
Viperfish: common questions
How does the viperfish hunt with fangs it cannot close its mouth around?
The viperfish's oversized fangs are a solution to the deep sea's central problem, that prey is rare and encounters are infrequent, so a predator must be certain of holding onto anything it manages to catch. When the viperfish lunges at prey, it opens its hinged jaws extremely wide, drives the long teeth into the prey on impact, and the backward-curving lower fangs, which reach almost to the eyes, then form a cage of teeth that the prey cannot wriggle out of. The fish then works the prey down its throat and swallows it whole, often an animal a large fraction of its own size, using its highly expandable stomach.
What is the glowing filament on a viperfish's back?
The very first ray of the dorsal fin is enormously elongated, sometimes about as long as the fish's whole body, and tipped with a photophore, a small organ that produces light through a chemical reaction. The viperfish is thought to hold this luminous filament forward and over its own head and to flash or wave the light, which in the pitch darkness of the deep sea acts as a lure, drawing small fish and crustaceans close enough to strike. This is the same basic hunting strategy as the anglerfish's illuminated lure, evolved separately, and it lets the viperfish catch prey while expending very little energy hanging motionless in the water.
Why does the viperfish need a shock absorber in its spine?
The viperfish attacks by lunging forward at high speed with its jaws wide open, and the sudden deceleration when its head and teeth hit the prey generates a strong jolt that could otherwise damage the fish's own skull and brain. To handle this, the first vertebra immediately behind the head is modified into a soft, flexible, cushion-like structure rather than a rigid bone, which flexes and absorbs the impact of each strike, working somewhat like a car's crumple zone. This adaptation lets the small fish strike with enough force to reliably impale prey without injuring itself in the process.
How deep does the viperfish live, and is it dangerous?
The viperfish spends daylight hours at depths of roughly 250 to 1,500 metres and undertakes a nightly vertical migration, rising to shallower water, often a few hundred metres deep, to feed where prey is more abundant, then descending again before dawn. It poses no danger to humans whatsoever, since it is only about 30 centimetres long, lives far below the depths people normally reach, and its fearsome-looking fangs are scaled for catching small fish. It has become one of the most recognisable deep-sea fish precisely because its appearance looks so menacing in photographs, but a full-grown viperfish is a small, fragile animal.