(Paris) Young eels swallowed by a fish managed to escape from the stomach of their predator by going through its gills, in reverse, according to a study published Monday in Current biology.
This is the first time that such a tactic has been recorded in the marine world, on video at that, according to a team of Japanese researchers.
She had already observed young Japanese eels survive by emerging from the gills of the fish that had swallowed them. But the researchers assumed that these apprentice Houdinis had found an escape route from their mouths before ending up in the stomach of their predator.
The team found to their “great surprise” that the eels had escaped from the fish’s stomach itself, the study’s lead author, Yuha Hasegawa of Nagasaki University, told AFP.
Stomach-churning
Some eels even found a way to circle the predator’s belly a few times before escaping, the study found.
To observe what happens in the stomach of the black sleeper, a freshwater fish common in Japan and Korea, the researchers injected it with a contrast agent suitable for X-ray analysis.
Of the 32 small eels swallowed by the fish, all but four attempted to escape, moving backwards through its esophagus to the gills.
From there, thirteen started to go through the queue, but only nine reached their goal.
The young eels were about seven centimetres long. The researchers noted that the animal, unlike most fish, is very good at swimming upside down.
An advantage to escape the trap in about a minute. Knowing that they could only survive the stomach acids for about three minutes.
Remarkably, the fish were not harmed by the escape maneuver. The experiment was “difficult” to carry out, and it took a year before the team got a convincing video of the eels’ feat.
A previous study had shown that worms can escape from the digestive system of frogs, but the exact process has never been captured on video.
Scientists are only beginning to understand the “mysterious and astonishing” strategies some animals use to escape predators, said study co-author Yuuki Kawabata, also of Nagasaki University.