It's unclear whether the fish is truly acting out of kindness for his friend, or if the behavior is something more simplistic. Japanese news outlet Hokkaido Shimbun Press contacted a local aquarium in regard to the behavior seen above, and experts there were stumped, too - but the clip is no less intriguing for that mystery.
In an op-ed for the New York Times, Jonathan Balcombe, the director of animal sentience with the Humane Society Institute for Science and Policy, suggests there's more complexity to fish that we're only now beginning to understand:
"As a biologist who specializes in animal behavior and emotions, I've spent the past four years exploring the science on the inner lives of fishes. What I've uncovered indicates that we grossly underestimate these fabulously diverse marine vertebrates. The accumulating evidence leads to an inescapable conclusion: Fishes think and feel."
And perhaps they even feel for one another, too.