Researchers at Nagasaki University and the Fisheries Research and Education Agency have used the same aquarium for predatory fish, donko and Japanese eel fry, in order to investigate the predatory avoidance behavior of Japanese eels, whose resources have decreased significantly in recent years. I have been conducting research to observe the offense and defense.

　During this study, I discovered that a Japanese eel, which should have been eaten by a predatory fish, was swimming in an aquarium by chance. I thought that it might have come out of the mouth of the predatory fish in some way, and continued to observe it. Even if it was caught by the predatory fish, more than half (54 out of 28; 51.9%) of the fry were Ella. It turned out that he had escaped to the outside of his mouth through the gap.

　Organisms that survive after being captured by predators by such active behavior are extremely rare, including taxa other than fish.Interestingly, the 28 fry that escaped all escaped from the tail, which may be related to the eel's specialty of backward swimming.

　This finding also gave new suggestions for the slender and slender shape of eels.It is hypothesized that the elongated shape evolved due to the use of narrow gaps and digging behavior, but in the proposal of a new hypothesis that "escape from the predator's mouth" promoted the evolution of the elongated shape. Was also connected.

　Currently, domestic fish are being released nationwide to restore the resources of Japanese eels.Small individuals with low ability to avoid predators are often preyed on by predators living in the stocking area, but the results of this study also consider eels that are easy to survive in order to obtain a high stocking effect. Expected to be useful.

Paper information:[Ecology] Escaping via the predator's gill: A defensive tactic of juvenile eels after capture