Black swallower fish live at depths of 700 - 3,000 m under the sea, have wide mouths, large bellies and teeth like spike traps to prevent prey from escaping.
A small larval fish (left) about to be swallowed by a black swallower (right). Photo: Paul Caiger/Woods Hole Oceanographic Institution
To ensure they don't miss their prey, the black swallower ( Chiasmodon niger ) has developed an impressive jaw and a balloon-like belly that allows it to swallow prey larger than itself. The fish is only 25cm long but can swallow fish twice its length and 10 times its weight.
Black swallowers are found in many parts of the world, including tropical and temperate waters of the Atlantic, Pacific, and Indian Oceans. However, it is necessary to dive very deep to observe a living individual. They are usually active at depths of about 700 - 3,000 m below the sea, where sunlight hardly reaches. Even today, with the increasing activities of deep-sea exploration and remote-controlled submersibles, people rarely see a black swallow in its natural habitat.
Black swallowers are solitary and 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 will quickly devour it with its wide open mouth. To prevent its prey from escaping, its mouth and palate are covered with sharp, interlocking teeth that point into the esophagus, acting like a spike trap.
However, this method of feeding is not perfect. Black swallowers have occasionally been seen floating on the surface of the water with their bellies about to burst from gas, though this is rare. This happens when the prey is so large that it begins to decompose before the predator can digest it.
Black swallowers can swallow prey larger than themselves. Photo: Lea Lee/Smithsonian
The black swallower was first reported in the early 19th century and appears in numerous accounts of ocean exploration in the decades prior. 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 Frank Thomas Bullen, published in 1904.
"The next notable monster is an example of a deep-sea Chimaera, Chiasmodon niger. In appearance, they are a nightmare, completely black, with a mouth that splits their head in two lengthwise," Bullen wrote.
"Their large mouths are equipped with effective teeth, not only in the jaws but also in the roof of the mouth. The incisors are hook-shaped and movable, so that while they can be pushed in to receive prey, they also prevent the prey from escaping. They can and do swallow fish larger than themselves - something that seems impossible, but it happens," Bullen wrote.
Thu Thao (According to IFL Science )
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