According to Australian Geographic, the black swallower is a deep-sea fish that lives more than a mile under the ocean's surface in tropical and subtropical waters. It grows to about 10 inches long, has no scales and swallows its prey, which are other fish, whole. Often, this fish attempts to eat other fish that are even bigger than it is.
The black swallower has a small, thin body that is a brownish-black color. Its teeth are sharp, with the lower ones protruding past the upper jaw. This fish eats its prey whole by opening its jaw wide and swallowing it, hence its name. While eating, its teeth move inward to give it room to feed. It is capable of swallowing fish up to twice its size because it has a distensible stomach that expands quite a bit.
However, there is a danger when the black swallower eats prey that is too large. In these cases, it cannot digest the fish before it starts to decompose inside its belly. This decomposition creates gases that stretch and eventually explode the black swallower's stomach, killing it instantly. Most of the knowledge scientists have gleaned from this fish comes from dead black swallowers with exploded guts that have floated to the ocean's surface..