Fangtooths are beryciform
fish of the family Anoplogastridae (sometimes spelled "Anoplogasteridae") that live in the deep sea.
The name is from Greek anoplo meaning "unarmed" and gaster meaning "stomach". With a circumglobal distribution in tropical and cold-temperate waters, the family contains only two very similar species in one genus, with no known close relatives.
The head is small with a large jaw and appears haggard, riddled with mucus cavities delineated by serrated edges and covered by a thin skin. The eyes are relatively small, set high on the head; the entire head is a dark brown to black and is strongly compressed laterally, deep anteriorly and progressively more slender towards the tail.
The fins are small, simple, and spineless; the scales are embedded in the skin and take the form of thin plates. As compensation for reduced eyes, the lateral line is well-developed and appears as an open groove along the flanks.
The pelagic fangtooths are among the deepest-living fish found as far as 5,000 metres (16,400 feet) down. They are more commonly found between 200 - 2,000 metres (660 - 6,560 feet) however, and juveniles apparently stay within the upper reaches of this range.
They may undergo diel migrations as is common with many deep-sea fish: by day these fish remain in the gloomy depths and towards evening they rise to the upper layers of the water column to feed by starlight, returning to deep water by daybreak. Fangtooths may form small schools or go alone. They are thought to use contact chemoreception to find prey, relying on luck to bump into something edible.