Eels escape from the gills of fish
Hasegawa et al./Current Biology
It has been found that Japanese eels attempt to escape from the stomachs of fish that have swallowed them whole, and sometimes succeed in doing so.
A few years ago, Yuba Hasegawa of Nagasaki University discovered that the Japanese eel (AnguillaAn eel (scientific name: Anguilliidae) that had been swallowed by a fish had somehow reappeared in the tank. Upon further investigation, it was discovered that the eels had escaped through the fish's gills — 28 of the 54 that had been swallowed whole had managed to escape — but it was unclear how they had managed to do so.
Hasegawa and his team were able to capture this process by injecting a contrast agent into the eels, making them visible under X-rays.Odontobutis obscura), and 12 were able to navigate far enough back up the esophagus to bend their tails and exit the gill slits. Nine of these 12 escaped.
When the eels began to move backwards through the esophagus, in some cases their tails were not fully inside the stomach, but in other cases their entire bodies were inside the stomach and they spun around as if searching for an exit. Five of the 11 eels that were fully inside the stomach were able to place their tails at the entrance to the esophagus and return to the gills.
Two of the 11 took a wrong turn and headed for the intestines. All that didn't escape died within three and a half minutes.
The team now plans to test whether other eels and similarly shaped fish can escape in this way. “At present, the Japanese eel is the only fish species that has been confirmed to be able to escape from the digestive tract of a predator after being caught,” Hasegawa says.
However, other kinds of animals can escape being swallowed whole. For example, aquatic beetles Regimbaltia attenuata You can escape from the frog Crawling out of the anus.
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Source: www.newscientist.com
