Japanese Eels Exhibit Remarkable Escape Mechanism from Predators

The Extraordinary Escape of Japanese Eels

For most creatures, being consumed by a predator typically signifies the end of their journey. However, Japanese eels have defied this grim fate in a remarkable manner. A study published on Monday in Current Biology reveals that juvenile Japanese eels possess an astounding ability to escape from within the stomach of a predatory fish.

Researchers observed these eels performing what can only be described as Houdiniesque escapes. Once swallowed, the young eels swim up the predator’s esophagus and make their way out through an opening in the fish’s gills, much to the predator’s dismay. This groundbreaking observation marks the first time scientists have documented such an escape mechanism from a predator’s stomach, prompting questions about whether other slender-bodied species might employ similar survival strategies.

The intriguing research began in 2021 when Yuha Hasegawa, then a graduate student at Nagasaki University, placed a young Japanese eel into a tank with a dark sleeper, a predatory fish known for its river-dwelling habits. To his astonishment, he witnessed the eel being swallowed whole. However, less than a minute later, the eel reappeared in the tank, leaving Hasegawa puzzled about how it had managed to escape.

As an assistant professor now, Dr. Hasegawa, alongside his colleague Yuuki Kawabata, an associate professor at Nagasaki University, dedicated the next three years to unraveling this mystery. Their quest for answers led them to employ advanced technology—a device capable of recording X-ray movies.

To conduct their experiments, the researchers injected dozens of young eels with a substance that made them easily identifiable under X-rays. They then placed these eels into a tank with the dark sleeper fish. As soon as the fish consumed the eels, the researchers would lightly anesthetize the fish and position it under the recording device. What they discovered was nothing short of astonishing.

The footage revealed a scene that most would find hard to imagine: a predator regretting its meal as much as this dark sleeper regretted swallowing the eel. Video by Hasegawa et al.