Fish
Fangtooth
Anoplogaster cornuta · also called fangtooth, common fangtooth
The fangtooth has the largest teeth, relative to its body, of any fish in the sea — so oversized that its lower fangs slide into sockets beside its brain just so it can close its mouth. It looks like a monster from the abyss, but a full-grown adult would fit in your hand.
Overview
Fangtooth live in the deep open ocean worldwide, typically 200 to 2,000 metres down and recorded far deeper. Only about 16–18 cm long, they are stocky, dark, and armed with disproportionately huge teeth, hunting fish and squid.
Teeth too big for its own mouth
The lower fangs are so long the fish evolved sockets beside its brain to sheathe the tips when its jaw closes — the most extreme teeth-to-body ratio of any fish.
Two lives in one
Juveniles are silvery, spiny, small-toothed filter-feeders, so different from adults they were once thought to be a separate species.
Status
The fangtooth is Least Concern, widespread through the world’s deep oceans and not targeted by fisheries.
Fangtooth: common questions
How big are the fangtooth's teeth compared to its body?
Relative to its overall body size, the fangtooth has the largest teeth of any fish in the ocean, with the two largest lower fangs being so long in proportion to the head that the fish could not physically close its mouth around them without a special adaptation. To solve this, the fangtooth has evolved a pair of pouch-like sockets located on either side of its brain, into which the tips of the lower fangs slide when the jaw is shut, effectively giving the fish somewhere to sheathe its own teeth so that its mouth can close completely despite the enormous fang length.
Why do young and adult fangtooth look so different?
Juvenile fangtooth are so unlike the adults, being silvery-grey rather than dark, having long protective spines projecting from the head, small rather than oversized teeth, and functional gill rakers used for filter-feeding on tiny plankton and crustaceans, that early naturalists classified the young and adult forms as two entirely separate species before their connection was recognised. As the fish matures, it loses the head spines, darkens to brown or black, develops its characteristic huge teeth, and switches from filter-feeding to actively hunting fish and squid, a transformation dramatic enough that the two life stages still look almost unrelated at a glance.
Why does a deep-sea fish need such enormous teeth if it is so small?
In the deep open ocean, prey is sparse and encounters with a potential meal can be separated by long stretches of empty water, so the evolutionary pressure is strongly toward not letting any prey item escape once it is within reach. The fangtooth's oversized teeth and wide gape maximise both the size of prey it can tackle and its grip on anything it catches, allowing a small fish to successfully seize and hold prey nearly its own size and swallow items that would be impossible for a similarly sized fish with ordinary teeth, an advantage that outweighs the awkwardness of housing such large fangs.
Is the fangtooth dangerous to humans?
Not at all, despite its genuinely fearsome appearance, which has made it a popular example of a nightmarish deep-sea creature in photographs and documentaries. It is a small fish, only about 16 centimetres long as a full-grown adult, and it lives at depths of hundreds to thousands of metres, far below where humans normally go, so encounters are essentially limited to specimens brought up in deep research trawls. Its teeth are adapted for gripping small fish and squid, and it poses no threat whatsoever to people, being far too small and living far too deep to be any kind of hazard.