Black Swallower: A Deep-Sea Fish That Gulps Prey Bigger Than Itself

You never know when your next dinner is coming in the deep sea. To ensure it never misses a meal, the black swallower fish has evolved a formidable jaw and a balloon-like belly that allows it to swallow prey much larger than itself. 

The black swallower (Chiasmodon niger) measures just 25 centimeters (about 10 inches) long, but it has been known to swallow fish that are more than double its length and 10 times its weight. 

They live in many parts of the world’s oceans, including tropical and temperate waters across the Atlantic, Pacific, and Indian Oceans. You’ll have to dive very deep to find one alive, though. The species typically dwells around 700 to 3,000 meters (3,000 to 10,000 feet) below the ocean’s surface at a depth where sunlight struggles to reach

Black swallowers are brilliantly adapted to life in the desolate abyss. Like a stealth bomber jet, its body is dark and scaleless to avoid detection by predators and prey alike. 

If the lone-ranging fish is lucky enough to find any prey in its unforgiving environment, it will swiftly gobble it up with its gaping mouth. To stop the swallowed victim from evading its guts, the mouth and palate are lined with sharp and interlocking teeth that point inwards towards the gullet, acting like a spiked trap. 

Its obnoxious method of eating isn’t perfect, however. Very occasionally, black swallowers can be found floating on the water’s surface with their stomachs nearly bursting with gas. This occurs when swallowed prey is so large it starts to decompose before the gluttonous host can digest it. 

Black swallowers were first reported in the early 19th century and appear in a fair number of written accounts about ocean exploration from decades gone by. One of the most colorful historical descriptions comes from a 1904 book called Creatures of the Sea: Being the Life Stories of Some Sea Birds, Beasts, and Fishes by Frank Thomas Bullen, a fascinating London-born author who wrote about life on the high seas.

It reads: “The next monster down for notice is a very good specimen of the deep-sea chimaera, Chiasmodon niger. It is a veritable nightmare in appearance, being entirely black in color, with a mouth that cleaves the head asunder laterally for its whole length, so that vulgarly speaking, when its mouth is wide open it has no profile.”

“Its immense mouth is furnished with equally effective teeth, which are not only found in the jaws but on the palate also. Its front teeth are hooked and movable, so that while they may be pushed inward to admit the entrance of prey, they effectually prevent it from coming out. This peculiarity is explained by a slight examination of the creature’s feeding habits. It can and does swallow entire fish actually larger than itself – which sounds impossible, but it is not. For the belly of this atrocious glutton is like an India-rubber bladder which may be expanded amazingly,” Bullen writes. 

Even in today’s world of deep-sea exploration and remotely operated submersibles, black swallowers are rarely ever seen alive in their natural habitat. Given their terrifying reputation, perhaps that’s not necessarily a bad thing…

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