The strange fish can swallow prey 10 times heavier than itself

Black swallower fish live at a depth of 700 - 3,000m in the sea with a wide mouth, large belly and teeth like barbed traps that prevent prey from escaping .

To ensure they don't miss their prey, the black swallower fish ( Chiasmodon niger ) developed impressive jaws and a ball-like abdomen that allows it to swallow prey larger than itself. This fish is only 25 cm long but can swallow fish that are twice as long and 10 times heavier.

A small larval fish (left) is about to be swallowed by a black swallower fish (right). (Photo: Paul Caiger/Woods Hole Oceanographic Institution).

Black swallower fish are distributed in many sea areas of the world , including tropical and temperate waters of the Atlantic, Pacific, and Indian Oceans. However, you need to dive very deep if you want to observe a living individual. They usually operate at a depth of about 700 - 3,000 m under the sea, where sunlight can hardly reach. Even today, with many deep-sea exploration activities and remote submersibles, people rarely see a black swallow fish in its natural habitat.

Black swallowers live alone and are very well adapted to life in deep water. Like a stealth bomber, their bodies are dark and scaleless to avoid detection by predators and prey.

If it finds any prey in this harsh environment, the black swallower fish will quickly eat it with its wide open mouth. To prevent prey from escaping, their mouth and palate are covered with sharp, interlocking teeth that point into the esophagus, acting like a barbed trap.

However, this eating method is not perfect. Sometimes people see black swallower fish floating on the water with their stomachs about to explode from bloating, although it is very rare. This occurs when swallowed prey is too large and begins to decompose before the hunter can digest it.

Black swallower fish can swallow prey larger than themselves. (Photo: Lea Lee/Smithsonian)

Black swallowers were first reported in the early 19th century and appear in many accounts of ocean exploration from previous decades. One of the most vivid historical descriptions is in the book Creatures of the Sea: Being the Life Stories of Some Sea Birds, Beasts, and Fishes by author Frank Thomas Bullen, published in 1904.

"The next notable monster is an example of the deep-sea Chimaera monster, Chiasmodon niger. In appearance, they are truly a nightmare with a completely black color, mouth splitting the head in half lengthwise" , Bullen write.

"Their wide mouth is equipped with effective teeth, not only in the jaw but also in the roof of the mouth. The incisors are hook-shaped and movable, so even though they can be pushed in to receive prey, the teeth are also helps prevent prey from escaping. They can and do swallow fish larger than themselves - something that seems impossible, but it still happens ," Bullen wrote.