The black swallower fish lives at depths of 700 to 3,000 meters in the ocean, featuring a wide mouth, large belly, and trap-like teeth that prevent prey from escaping.
To ensure it doesn’t miss its prey, the black swallower (Chiasmodon niger) has developed an impressive jaw structure and a balloon-like belly that allows it to swallow prey larger than itself. This species measures only 25 cm in length but can consume fish that are more than double its size and ten times its weight.
A small larval fish (left) about to be swallowed by a black swallower (right). (Photo: Paul Caiger/Woods Hole Oceanographic Institution).
The black swallower is distributed across various ocean regions, including tropical and temperate waters of the Atlantic, Pacific, and Indian Oceans. However, one must dive very deep to observe a live specimen. They typically operate at depths of about 700 to 3,000 meters, where sunlight barely reaches. Even today, with many deep-sea exploration activities and remotely operated submersibles, sightings of a black swallower in its natural habitat remain rare.
Black swallowers are solitary creatures that have adapted exceptionally well to life in the deep sea. Like a stealth bomber, their dark bodies lack scales to avoid detection by predators and prey alike.
If they encounter any prey in this harsh environment, black swallowers quickly feast with their wide-open mouths. To prevent prey from escaping, their mouths and palates are lined with sharp, interlocking teeth that point inward toward the esophagus, functioning like a trap.
However, this feeding method is not foolproof. Occasionally, black swallowers are spotted floating at the surface with their bellies close to bursting from gas buildup, although this is quite rare. This occurs when the swallowed prey is too large and begins to decompose before the predator can digest it.
The black swallower can consume prey much larger than itself. (Photo: Lea Lee/Smithsonian)
The black swaller was first reported in the early 19th century and has appeared in various ocean exploration accounts from decades past. One of the most vivid historical descriptions can be found in the book Creatures of the Sea: Being the Life Stories of Some Sea Birds, Beasts, and Fishes by Frank Thomas Bullen, published in 1904.
“The next remarkable monster is an example of the deep-sea Chimaera, Chiasmodon niger. In appearance, it is truly a nightmare with its completely black body and its mouth split longitudinally,” Bullen wrote.
“Their wide mouths are equipped with effective teeth, not only in the jaw but also in the palate. The hook-shaped and movable incisors, while capable of being pushed inward to receive prey, also help to prevent it from escaping. They can and indeed have swallowed fish larger than themselves – an act that seems impossible, yet it occurs,” Bullen wrote.
