Very few specimens of Malacosteus niger have been observed alive in their natural habitat but we are able to deduce something about the fish's behaviour from its appearance and structure.
Like many of its dragonfish relatives, M. niger has a very large mouth relative to its body size - the lower jaw takes up over 20% of its length.
The head can hinge backwards at the top part of the neck allowing the lower jaw to shoot out and impale smaller fishes or crustaceans with its large sharp fangs. The jaw is then withdrawn and the prey is fed into the throat using pharyngeal teeth located in the neck.
The lower jaw has no floor, or ethymoid membrane, and this is thought to perhaps reduce resistance as it flies through the water.
The location of the fins give another clue to the fish's predatory lifestyle. Like a pike, the dorsal and anal fins are located near the tail which allows the fish to suddenly dart forward and attack. The tail is quite small and the lower lobe slightly larger - this helps the fish generate some upward movement as it moves through the water.
Many midwater fishes undergo a large vertical migration upwards at night following the smaller organisms on which they feed, in some cases all the way to the surface. Unlike the majority of the other 220 or so species of dragonfishes, M. niger does not do this and chooses to spend most of its time between 500-1000m, where its preferred prey items are found.