Off the coast of Eilat, Israel, a Pacific day octopus did something no scientist had seen before. Mid-hunt, with a small group of fish swimming alongside it over a coral reef, the octopus picked up a rock and placed it directly into the mouth of a partner fish. The moment, captured on video, is now at the center of a peer-reviewed study that describes the most detailed picture yet of how octopuses and fish cooperate to find food.
The research, led by marine biologist Eduardo Sampaio of the Max Planck Institute of Animal Behavior and published in Nature Ecology & Evolution in late 2024, used three-dimensional underwater tracking to follow individual octopuses and their fish companions through real hunts on Red Sea reefs. The technology recorded each animal’s position, speed, and orientation in three dimensions, producing data far more precise than anything available from earlier diver observations or lab experiments.
What the tracking revealed upends a long-held assumption. These mixed-species hunting parties are not loose, accidental gatherings. The octopus is running the show.
The octopus as hunt leader
Interspecies hunting partnerships on coral reefs are not new to science. Groupers have been documented signaling to moray eels to flush prey from crevices, and various reef fish trail behind foraging octopuses to snatch escaping prey. But Sampaio’s study is the first to quantify who is actually leading these groups and how group makeup affects whether the hunt succeeds.
The answer, drawn from dozens of tracked hunts, is that octopuses exert what the authors call “multidimensional social influence.” In plain terms, the octopus does not just chase prey in the same direction as nearby fish. It initiates directional changes that fish then follow. It controls spacing, positioning itself to corral prey into zones where both it and its partners can strike. And it appears to shape the composition of the group itself, tolerating certain fish species while driving others away.
That last point proved critical. The data showed that specific combinations of fish species hunting alongside the octopus produced significantly better outcomes than others. Some fish contributed by flushing prey from hiding spots. Others seemed to freeload, benefiting from the octopus’s efforts without adding value. The octopus responded accordingly. In footage from the same research program, Sampaio and colleagues previously documented octopuses punching fish that were not pulling their weight, a blunt enforcement mechanism that keeps the hunting party functional.
The 3D tracking made these patterns visible in a way that anecdotal observation never could. By measuring who moved first, who followed, and how tightly each fish species coordinated with the octopus, the researchers built a statistical case that the octopus occupies a genuine leadership role. They define that term carefully: leadership here means measurable influence over group movement and structure, not a subjective impression of dominance.
A rock, a fish, and an open question
Then there is the rock. During one recorded hunt, the octopus picked up a small stone and inserted it into the mouth of a fish swimming beside it. The footage is striking, and it has drawn attention well beyond the marine biology community. But the behavior sits in a different evidentiary category than the tracking data that forms the study’s backbone.
Octopuses are well-known object manipulators. They carry coconut shells as portable shelters and stack rocks to barricade their dens. Placing an object into another animal’s mouth during a cooperative hunt, however, is something else entirely. It implies some awareness of the partner’s role and an intent to alter that partner’s behavior, qualities that would push the interaction toward genuine tool-mediated communication.
The published paper does not provide a frame-by-frame breakdown of the rock-placement sequence. Key details remain unresolved: how many times the behavior occurred across the study’s field sessions, whether it involved multiple fish species or just one, and whether the octopus appeared to pause or adjust its grip before acting. Without those qualitative notes, scientists cannot yet distinguish a deliberate tactic from an incidental contact, an octopus handling debris near a fish that happened to be close.
Sampaio and his co-authors appear aware of this ambiguity. Their paper’s central argument rests on the repeatable tracking data, not on the rock footage. The title focuses on “social influence,” “leadership,” and “composition-dependent success,” all claims supported by statistical models applied across many hunts. The rock incident fits within that framework as a vivid example of how octopuses might exert influence, but the paper does not depend on it. That restraint is a mark of disciplined science.
What would settle the debate
For the rock behavior to move from provocative anecdote to established finding, researchers would need to document it repeatedly, ideally across multiple reefs, seasons, and individual octopuses. A single filmed event, no matter how dramatic, cannot tell us whether this is a population-level hunting tactic, a rare innovation by one unusually creative individual, or something in between.
Future fieldwork could also clarify the mechanism. Did the rock block the fish from eating prey the octopus wanted for itself? Did it reposition the fish closer to a target? Or was it a form of signaling, a physical nudge that changed the fish’s behavior in a way that benefited the group? Each interpretation carries different implications for how we understand octopus cognition, and each requires different kinds of evidence to support.
What is already clear, as of June 2026, is that the broader findings do not need the rock to be remarkable. The 3D tracking data alone demonstrates that octopuses on Red Sea reefs actively organize mixed-species hunting parties, lead group movements, influence which fish join the hunt, and achieve better results with certain team compositions. Those conclusions are peer-reviewed, quantified, and replicable.
Why this changes what we know about reef intelligence
For decades, complex social coordination was treated as the domain of big-brained vertebrates: primates, dolphins, corvids. Octopuses complicated that picture because they are invertebrates with distributed nervous systems, most of their neurons located in their arms rather than a centralized brain. The idea that such an animal could lead a multispecies hunting group, recruit useful partners, punish freeloaders, and possibly use objects to direct allies was, until recently, outside the boundaries of what most researchers considered plausible.
Sampaio’s work does not claim octopuses are “intelligent” in a general sense. It makes a narrower, more defensible argument: in measurable terms, octopuses change the behavior of the animals around them in ways that affect group outcomes. Whether that influence arises from flexible cognition, learned routines, or something else entirely is a question the data cannot yet answer. But the influence itself is no longer in doubt.
For anyone who has watched an octopus on a reef, none of this is entirely surprising. Divers have long reported that octopuses seem to be aware of the fish around them, sometimes tolerating certain species and chasing off others. What this study adds is measurement. It replaces impressions with coordinates, anecdotes with statistics, and speculation with a framework that other researchers can test, challenge, and build on. The rock in the fish’s mouth may or may not turn out to be the breakthrough moment. The data behind it already is.
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*This article was researched with the help of AI, with human editors creating the final content.
