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A specimen of the black swallower fish, which can consume prey so big that it may decompose in its stomach. Image Credit: Museum of Comparative Zoology, Harvard University

The black swallower

  • November 28, 2013

This impressive fish could swallow prey more than twice its length and 10 times its mass.

Contributor
Becky Crew

Becky Crew is a Sydney-based science communicator with a love for weird and wonderful animals. From strange behaviours and special adaptations to newly discovered species and the researchers who find them, her topics celebrate how alien yet relatable so many of the creatures that live amongst us can be.

Life at 2.7 km below the surface of the ocean can be tough. Food this far down is pretty scarce, so most deep-sea creatures need to turn just about anything they come across into a meal. The black swallower (Chiasmodon niger) can turn a fish more than twice its length and 10 times its own mass into just that.

Slender, scaleless and at just 25cm long, the black swallower is found in tropical and subtropical waters in the north and south-western Atlantic Ocean, and it has the perfect body for devouring other bony fishes whole. It has a large mouth for engulfing its prey, and both its jaws and palate are covered in sharp teeth to give it the perfect grip.

It has several long, hooked front teeth that can be pushed inward to allow the prey to move through its jaws, and then pushed backwards to lock it inside. The prey makes its way down into a specialised gut that can distend so far that it hangs well below the rest of the body as the stomach tissues are stretched into transparency.

While the idea is now to live off this meal for some time, the prey can sometimes be so large that the black swallower can't digest it before decomposition sets in. The release of gasses in this situation causes the black swallower's gut to inflate and burst, and it floats dead and belly-up to the surface.

This is how most black swallower specimens are found, most recently in 2007 off the South Coast of Grand Cayman, which is the largest of the three Cayman Islands. Inside the severely stretched stomach of this dead black swallower was a snake mackerel (Gempylus serpens), and at 86 cm long, this meal was more than four times the length of its predator.

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