Watch Japanese eels escaping alive from predator’s stomach

By Stephen Beech via SWNS

Slippery Japanese eels are able to escape alive from a predator’s stomach.

Remarkable footage is the first video evidence of the "unique" survival method of the young eels after being swallowed whole.

X-ray videography shows how they back their way out, first inserting the tips of their tails through the esophagus and gills before pulling their heads free.

Scientists say many species have defensive tactics to escape being eaten by would-be predators.

But the new study, published in the journal Current Biology , has taken it to another level by offering the first "astonishing" video evidence of Japanese eels, Anguilla japonica, escaping after being swallowed alive.

Dr. Yuuki Kawabata, of Nagasaki University in Japan, said: “We have discovered a unique defensive tactic of juvenile Japanese eels using an X-ray video system.

"They escape from the predator’s stomach by moving back up the digestive tract towards the gills after being captured by the predatory fish.

“This study is the first to observe the behavioral patterns and escape processes of prey within the digestive tract of predators.”

In an earlier study, the Nagasaki University team had shown that Japanese eels can escape from the gills of predators after being swallowed.

But they didn't know how the process worked.

Study co-author Yuha Hasegawa said: “We had no understanding of their escape routes and behavioral patterns during the escape because it occurred inside the predator’s body."

For the new study, the researchers found a way to see inside the predatory fish, Odontobutis obscura, using an X-ray videography device.

To visualize the eel after it had been eaten, they had to first inject them with a contrast agent.

But it still took the team a year to capture convincing video evidence showing the escape process involved.

Their videos show that all 32 captured eels had at least part of their bodies swallowed into the predators' stomachs.

After being swallowed, all but four tried to escape by going back through the digestive tract toward the esophagus and gills.

Of those, 13 managed to get their tails out the fish gill, and nine successfully escaped through the gills.

It took the escaping eels an average of around 56 seconds to free themselves from the predator’s gills, according to the findings.

Dr. Kawabata said: “The most surprising moment in this study was when we observed the first footage of eels escaping by going back up the digestive tract toward the gill of the predatory fish.

“At the beginning of the experiment, we speculated that eels would escape directly from the predator’s mouth to the gill.

"However, contrary to our expectations, witnessing the eels’ desperate escape from the predator’s stomach to the gills was truly astonishing for us.”

Further research found that, despite the similarities, the eels didn’t always rely on the same escape route through the gill cleft.

Dr. Kawabata said some of them also circled along the stomach, seemingly in search of a way out.

The study is also the first to captured the behavior of any prey inside the digestive tract of its predator, according to the researchers.

They say that the X-ray methods used in the study can now be used to observe other predator-prey interactions.