(Sampaio et al., Ecology, 2020)

Octopuses Observed Punching Fish, Perhaps Out of Spite, Scientists Say

21 DECEMBER 2020

In new proof that 2020 has been a crappy year basically everywhere, scientists have captured video evidence of octopuses randomly punching at fish, possibly for no reason other than being spiteful.

 

While this remarkable, rather nasty-sounding behaviour might seem like it comes from a place of direct conflict between different animal species, that's not the whole story, researchers say.

In fact, this antisocial fish-punching phenomenon – which scientists term "active displacement" of fish – occurs in the midst of collaborative hunting efforts, in which octopuses and fish team up to chase and trap prey together.

"Octopuses and fishes are known to hunt together, taking advantage of the other's morphology and hunting strategy," explains marine biologist Eduardo Sampaio from the University of Lisbon in Portugal.

"Since multiple partners join, this creates a complex network where investment and pay-off can be unbalanced, giving rise to partner control mechanisms."

In much the same way as you or I might try to elbow-out fellow diners at a buffet, this 'partner control mechanism' therefore seeks to establish a sense of control and dominance in a food free-for-all.

 

It's just that partner control – when delivered by an octopus – is a tad more brutal than your average buffet queue experience.

"To this end, the octopus performs a swift, explosive motion with one arm directed at a specific fish partner, which we refer to as punching," the researchers explain in a new paper.

In their study, Sampaio and his team observed interactions between Octopus cyanea and a number of different fish species in the Red Sea, including tailspot squirrelfish (Sargocentron caudimaculatum), blacktip (Epinephelus fasciatus) and lyretail (Variola louti) groupers, among others.

"Multiple observations involving different octopuses in different locations suggest that punching serves a concrete purpose in interspecific interactions," the team writes.

"From an ecological perspective, actively punching a fish partner entails a small energetic cost for the actor (i.e. octopus), and simultaneously imposes a cost on the targeted fish partner."

The researchers hypothesise that much of the punching is designed to essentially keep fish in line during hunts, whether deterring them from prey, relocating their position in the pack, or even evicting them from the hunt altogether.

 

Sometimes, in cases where hanger-on fish are not contributing to the hunt – basically acting as parasites hoping to reap the spoils of others' labour – an octopus might punch a fish on the basis of simple competition, the team suggests, in order to gain better access to the prey itself.

But fish-punching doesn't always seem to occur for immediately practical reasons. On two occasions, the researchers observed punching take place even when the sudden strike didn't appear to be related to prey-securing attempts.

"In these cases, two different theoretical scenarios are possible. In the first one, benefits are disregarded entirely by the octopus, and punching is a spiteful behaviour, used to impose a cost on the fish," the researchers write.

"In the other theoretical scenario, punching may be a form of aggression with delayed benefits (i.e. direct negative reciprocity or punishment), where the octopus pays a small cost to impose a heavier one on the misbehaving partner, in an effort to promote collaborative behaviour in the following interactions."

While we can't yet know for sure why octopuses are randomly punching fish like this, at least one of the theoretical explanations given suggests octopuses may have some serious attitude.

In any case, it's clear there's a lot more to learn about this phenomenon, and the complex relationships at work during these underwater collaborations/fisticuffs.

"Detailed quantitative analyses of these multi-specific hunting events can explore several other important ecological questions," the researchers explain, "such as the potential existence of privileged relationships between octopuses and specific fish partners (e.g. are some species or individuals more punched than others?), and how individual dynamics are modulated by the network of social interactions (e.g. do fishes also provide feedback to each other?)."

The findings are reported in Ecology.