Black Swallower Identification Guide

Key identification features

• Slender, elongated body covered in smooth, scaleless, blackish-brown to jet-black skin
• Large head with a wide gape and long, thin, backward-curving needle-like teeth
• Extremely distensible stomach that can balloon to several times the fish's own body size after swallowing oversized prey
• Small eyes and a single long-based dorsal fin set well back on the body
• Typically small overall, rarely exceeding about 25 cm in length
• No barbels, photophores, or luminous lure of any kind

Common look-alikes

• Kali species (fangtooth swallowers, family Chiasmodontidae): closely related and similarly dark and toothy, but with a shorter dorsal fin base and a more compressed head profile.
• Snake mackerels (Gempylidae): also dark and elongated, but show small separate finlets behind the dorsal and anal fins that the black swallower lacks.
• Cutlassfish: ribbon-thin and toothy, but far more laterally compressed and silvery rather than uniformly black.

Where you'll see one

The black swallower ranges throughout mesopelagic and bathypelagic waters of tropical and temperate oceans worldwide, generally between about 700 and 2,700 meters, where its oversized stomach lets it exploit rare, infrequent meals in a food-scarce environment.