Watch an octopus punch a fish in the face

Octopuses are some of the smartest invertebrates in the animal kingdom, with an exceptional ability to solve problems, use tools, and recognize their surroundings and individual people. Over the years, aquariums have told stories of their octopuses escaping their enclosures or shooting water at bothersome lights to put them out.

Now, thanks to videos from a team of researchers, we have learned about another octopus skill: punching unsuspecting fish in the face.

The team, led by marine biologist Eduardo Sampaio, published their observations in the journal Ecology on December 18. The researchers watched octopuses in the Red Sea punching at fish, at times for no apparent reason, despite the fact that they were supposedly cooperating with the fish on a mutual hunt.

"Octopuses and fishes are known to hunt together, taking advantage of the other's morphology and hunting strategy," explained Sampaio on Twitter. "Since multiple partners join, this creates a complex network where investment and pay-off can be unbalanced, giving rise to partner control mechanisms."

'Partner control mechanisms' meaning fish abuse, in this case.

"We found different contexts where these punches (or directed explosive arm movements, if you want to get technical about it) occur," added Sampaio, "including situations where immediate benefits are attainable, but most interestingly in other contexts where they are not!"

Most of the time, the researchers wrote, the octopuses appeared to have a purpose behind hitting fish. It could be to keep fish away from prey, putting unruly fish in their place, or kicking out mooching fish that aren't helping with the hunt.

But the marine biologists noticed a couple curious instances where the octopus had no real reason to whack a fish, leading the team to theorize that the "punching is a spiteful behaviour." From a purely ecological standpoint, there's little benefit for randomly smacking a fish. It takes energy to hit a hunting partner and the hunting partner loses energy from getting hit. It wouldn't make sense to waste energy like that.

The team hypothesized it could be a form of aggression simply meant to keep fish down or pre-emptively punishing misbehaving fish. But more studies are needed before researchers can fully figure out this underwater fight club.