The Pacific viperfish, Chauliodus macouni, is a predatory fish living deep in the oceans and is frequently referred to as among the ocean's "bottom feeders." In daytime it can be found from 200–5000 m below the ocean surface. At night it swims up into shallower depths of less than 200m where food is more plentiful. Pacific viperfish will mostly eat crustaceans and small fish. They typically reach lengths of up to 1 foot and are considered an example of deep-sea gigantism. It is believed that its first dorsal fin's photophores are used to attract prey.
Pacific viperfish can be characterized by its large mouth, long fang-like teeth and long dorsal fin ray (as much as half its body length). They are iridescent dark silver-blue color in life with pale fins. They can also be a light black color with blue fins.