Scientists like to use the size of an animal's brain relative to its body to judge how intelligent an animal is. This is calledbrain to body ratio, the larger the data, the smarter the animal is considered to be. Although this method is crude, it makes sense because it provides feedback on how much the animal has "invested" in its brain.


Octopuses are often known for their intelligence, and their brain-to-body ratio is very good—their brain-to-body ratio is the largest among invertebrates, even larger than many vertebrates.

In addition, octopuses have about the same number of neurons as a pet dog—the average octopus has about 500 million neurons, about two-thirds of which are located in its tentacles.


In addition to these "hardware" performances, in the laboratory, octopuses can walk through mazes, recognize human faces, use various methods to confuse opponents, and use various tools.

All of these are showing their intelligence to the world, but a recent study pointed out that octopuses are much more than these abilities.They also look for "fish slaves" to help them hunt.

Scientists discovered in the Red Sea a species calledBig blue octopus (Octopuscyanea)They will look for some fish to help them hunt, and they will also use their tentacles to beat those fish that are passive and slow to keep them motivated, and beat and drive away those fish that want to touch fish but are not working.


Unique behavior of octopus captured underwater

Relevant research was published in the journal Nature Ecology and Evolution on September 23 this year.

It is not easy to find and film the hunting behavior of octopuses, because octopuses are good at camouflage and are very cautious. Only when they are familiar enough and accustomed to the camera will they put down their guard and hunt normally.

The researchers for this study spent about a month diving in a coral reef off the coast of Eilat in the Red Sea, accumulating a total of 120 dive hours and recording 13 octopus hunts using several cameras - a total of three to four hours.


△Big blue octopus ©Ahmed AbdulRahman

The researchers found that in all octopus hunting behaviors, each octopus was accompanied by a school of two to 10 fish.

Hunting groups that cooperate with octopuses usually include several types of coral fish, such as groupers and scarlet salamanders. The number of each fish species varies in each hunt. The only thing that is the same is that there is only one octopus.

The researchers fed these hunting scenes into software to create three-dimensional images, then used another program to track each animal in the hunting scene and record its position relative to other animals to determine their purpose.

Ultimately, it was discovered that during cooperative hunting,The fish is responsible for finding prey and directing the octopus where to move, while the octopus ultimately decides if and when to move.


The fish will tell the octopus in which direction there is prey, usually in the crevices of rocks that are difficult for them to catch, and the octopus can use its tentacles to pull the prey out of the crevices.

Octopuses' unique cross-species cooperation

While cross-species cooperative hunting is uncommon in nature, it does occur, such as in badger-coyote alliances, mixed-bird alliances, and moray eel-grouper alliances.


△Typical cross-species cooperation between coyotes and badgers

These cross-species cooperations are usually complementary, allowing each other to eat prey that cannot be eaten when hunting alone, and at the same time, each other saves more effort.

The same is true for octopuses and fish. The fish gets prey that can only be reached by the octopus's tentacles, and the octopus completely lets the fish help it find its prey without having to hunt opportunistically. This saves time and effort for the octopus.

In addition, in cross-species cooperation,There is no priority when eating, whoever catches the prey first will eat it, but they will continue to cooperate until everyone has eaten the prey. The same is true for the cooperation between octopuses and fish.

However, the hunting alliance of octopus and fish also has its own unique parts.

The cooperation between the two is more like an octopus looking for a "fish slave" to do things, because the octopus will beat up the fish that don't work hard, and really determines where the group hunts and whether to cooperate.


When cooperating, fish sometimes surround the octopus and do nothing else, or have their own ideas and do not look for prey. At this time, the octopus will beat these fish angrily and keep flicking them with its tentacles. The beaten fish will become active again and start to move around to find prey as if they are shocked. Only when the fish go to the coral reefs to look for prey, the octopus will be satisfied and will not beat them.

Among them, the one who was beaten the most by octopus wasblackfin grouperLater, scientists discovered that these fish were not here to cooperate in hunting at all. They were just fishing, not actively looking for prey at all, and just waiting to snatch the prey when it appeared.


In addition, some fish will also attack fish that don’t work hard.However, no fish attacks on octopuses have been observed.- And this is obviously not because the octopus is stronger, but because the octopus plays a more important role in this alliance.

It is worth mentioning that this study is not yet sure whether the octopus recognizes which fish are its partners, because during cooperative hunting, fish often come in and replace other fish.

In addition, it is not certain whether this behavior of octopuses is innate or acquired, but researchers believe that it is more likely to be acquired, because small octopuses are obviously not as skillful as large octopuses in this behavior.


at last

You'll find that the cross-species cooperation between octopuses and fish is more like the cooperation between humans and hounds than other cross-species cooperations that are inflexible in using social information to change strategies.

Of course, this may have something to do with the fact that octopuses are really smart.

There is a famous theory of the evolution of larger brains in animals - known associal brain hypothesis,The theory is that animals evolved larger brains to process social information and cooperate with others.

However, the octopus is the biggest exception to this theory. Unlike many intelligent animals, octopuses are solitary animals. They like to be alone and have no social structure.

Therefore, why octopuses have become so smart has always puzzled scientists.

But there are only two possibilities, either octopuses have methods other than social information that lead to high intelligence, or scientists have ignored the octopus's lifestyle that is consistent with the social brain hypothesis.

This study seems to lean slightly toward the second possibility, that octopuses and fish hunt cooperatively, demonstrating that at least one species of octopus has a fairly rich social life.

Original report: https://www.nbcnews.com/science/science-news/octopuses-hunt-with-fish-punch-video-rcna171705

Literature: https://doi.org/10.1038/s41559-024-02525-2