The Great Escape

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For some animals, ending up in the belly of their predators is not always the end.

Japanese scientists recently discovered a species of eel that is able to pull off an elaborate escape after being swallowed by predatory fish.

Researcher Yuha Hasegawa first noticed this unusual maneuver when he released a young Japanese eel – known as Anguila japonica – into a tank with a dark sleeper, a predatory river fish. Hasegawa witnessed the sleeper gobbling up the juvenile eel. However, less than a minute later, the eel was swimming around the tank.

“We had no understanding of their escape routes and behavioral patterns during the escape because it occurred inside the predator’s body,” he explained in a statement.

Hasegawa and his colleagues later conducted a study to understand how the eels pulled off their great escape from the belly of the beast.

They injected 32 eels with a contrast agent that would light up under an X-ray and placed them in the tank with a dark sleeper. They then used a special device that recorded X-ray movies and figured out how these escape artists did it.

“We thought the eel escaped from the mouth of the predator, but in the first footage we recorded the eel escaped from the stomach of the predator,” Hasegawa told the New York Times. “It moved back up the digestive tract toward the gill of the fish.”

Still, it wasn’t easy and the success rate was low: Twenty-eight eels attempted the escape and only nine succeeded.

Time was of the essence, too: The eels spent 56 seconds on average in the attempt to escape.

The researchers explained that A. japonica is built for such escapes, adding that its elusive methods are also uncommon compared with other escape artists in the animal kingdom.

For example, the bombardier beetle sprays a noxious fluid when stuck in the stomach of a toad.

Meanwhile, this study marks the first time scientists have captured footage of a prey species escaping from inside a predator’s digestive tract.

The authors hope to learn more about how such maneuvers might have evolved in eels and whether other species have adapted in similar ways.