Fangtooth

Fangtooths are beryciform fish or ray-finned fish. They are so called because they possess lepidotrichia or "fin rays"; their fins being webs of skin supported by bony or horny spines. They are of the family Anoplogastridae and live in the deep seas worldwide.

Fangtooths are quite small and harmless to humans, despite their menacing look and large, fang-like teeth. They can be as small as 8 centimeters and reach a maximum length of just 16 centimetres.

In adults, the largest two fangs of the lower jaw are so long that the fangtooths have evolved a pair of opposing sockets on either side of the brain to accommodate the teeth when the mouth is closed.

They have the largest teeth of any fish in the ocean, proportionate to body size.

The pelagic fangtooths are among the deepest-living fish found as far as 5,000 metres down. They are more commonly found between 200 - 2,000 metres however, and juveniles apparently stay within the upper reaches of this range.

By day these fish remain in the gloomy depths and towards evening they rise to the upper layers of the water column to feed and return to deep water by daybreak. These fish are voracious sit-and-wait predators and swallow their prey whole; they have been observed feeding on fish 1/3 of their own size.
They are thought to use contact chemoreception to find prey, relying on luck to bump into something edible.
The smaller teeth and longer gill rakers of juveniles suggest they feed primarily by filtering zooplankton from the water, while the deeper-living adults target other fish and squid. The fangtooths' oversized teeth and mouths are thought to be an advantage in these lean waters where anything encountered (even if it is larger than the fish) must be considered a possible meal. The fangtooths in turn are preyed upon by other large pelagic fish, such as tuna and marlin.

Fangtooths are known to be robust when compared to many other deep-sea fish; they have been kept alive for months in aquariums despite conditions which are significantly different from their usual deep-sea habitat.