PARIS: Eels that have been swallowed by fish have been recorded for the first time sliding tail-first back out of their would-be predators’ stomach and escaping out of their gills, a study said on Monday.

The remarkable last-gasp getaway also marks the first time this kind of defensive tactic has been caught on video across the animal kingdom, according to the Japanese researchers.

The team behind the new study had already observed young Japanese eels surviving being eaten by sliding out of the gills of fish — rather than out of the mouths that had swallowed them.

Nonetheless, the researchers had assumed the eels had been somewhat near the mouths of the fish when they broke free. But the team was “really surprised” to find that the eels were all the way in the stomach of their predators before starting their escape bid, lead study author Yuha Hasegawa of Nagasaki University said.

Some eels even circled around the stomach several times before wriggling free, according to the study in the journal Current Biology. To see what was happening inside the bodies of the predatory dark sleeper fish, the researchers injected them with fluid to increase the contrast for recording the results on an X-ray video system.

Out of 32 eels swallowed into the stomachs of the fish, all but four tried to escape by backing out through the digestive tract, towards the esophagus and eventually out the side door of the gills, the study said.

Published in Dawn, September 10th, 2024