Researchers have made a spectacular observation: for the first time, images document how an animal manages to escape from the digestive tract of a predator. Young Japanese eels can first swing their thin tail tip back into the esophagus and from there, go backwards via the gills to freedom.
Researchers from Japan’s Nagasaki University were able to document the behavior for the first time using video X-rays. This defense tactic is unique, says research team member Yuuki Kawabata.
First documented escape from a predator’s stomach
“This study is the first to observe the behavioral patterns and escape processes of prey in the digestive tract of predators,” the report said. In a previous study, the team had already shown that juvenile Japanese eels (Anguilla japonica) escape from the gills of the freshwater predatory fish Odontobutis obscura. However, the exact escape route was unclear because the researchers could not see inside the fish.
Nine of the 32 eaten eels managed to escape
For the new study, published in the journal Current Biology, the researchers injected the young eels with a contrast agent to make them visible on the images. In total, they saw that 32 young eels were at least partially swallowed. Of these, 28 tried to escape via the esophagus. Nine managed to escape.
“At the beginning of the experiment, we suspected that the eel would escape directly from the predator’s mouth into its gills,” Kawabata said. “However, contrary to our expectations, we were surprised to see the eel desperately escape from the predator’s stomach into its gills.”
Eels have only a few minutes to escape
Escape can also be successful because the predatory fish quickly swallow their prey whole with water. If the young eels remain in the digestive tract, they are killed by the highly acidic and anaerobic environment. After three to four minutes, the eels in the stomach usually stop moving – unless they find the exit first.
The eel is seriously threatened worldwide
Japanese eel is widespread in Japan and China. However, their populations are declining and they are listed as critically endangered on the Red List.
Like the European eel, young Japanese eels swim from the sea into rivers and ascend to the upper reaches of the river and into mountain lakes. After a few years in fresh water, they migrate downstream and reach the sea, where they spawn.
Source: Krone
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