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How Big Is A Fish Brain? Memory & Intelligence Facts!

Lindsey Stanton Profile Picture

By Lindsey Stanton


Most people think that fish are really stupid and brainless animals, but that is not quite the case. Okay, so yes, they are not as smart as some other creatures on this planet, mainly humans and other mammals. However, they are also not as dumb as most people would think, at least not for the most part.

The fact of the matter is that there are some pretty intelligent fish out there, and there is indeed evidence to suggest that fish are not brainless. So, how big is a fish brain, and what can it do? These are the questions we are here to answer today, so let’s get right to it. The question of “how big is a fish brain?” is indeed relatively impossible to answer. There are different sizes of fish, and they can vary greatly from very small sardines to massive tuna and sharks.

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The Size Of A Fish Brain

an albino rainbow shark in a tropical aquarium
Image credit: FoxPix1, Shutterstock

Ok, so most fish have physically smaller brains than human beings, which is in part because they tend to be comparatively small. Yes, there are some pretty big fish out there, but when compared to human beings, most are smaller.

So, it does make sense that fish brains are, on average, comparatively smaller than that of humans. On that same note, even if one considers the size difference between a fish and a human, fish do have smaller brains.

However, this does not mean that they are stupid, not at all. When it comes to the weight and size of the brain compared to other vertebrates, fish do have smaller brains, about a fifteenth of the comparative size of a bird or small mammal. That being said, sharks and other such fish have about the same brain-to-body ratio as many birds and small mammals.

Therefore, there is no average size brain for a fish. That being said, fish brains are quite small, but this does not mean that they are brainless. There are indeed some fish that are known to have a good memory, cognitive abilities, the ability to construct things, and other such skills too.

This means that somewhere in that fish brain, there has to be some sort of intelligence. They are not as smart as human beings, but there are fish out there that are fairly adept in terms of mental abilities.

Let’s now go over some examples which illustrate that fish do possess a certain level of intelligence.


Fish Memory

Indeed, there are fish out there that show some signs of mental life, especially in terms of short and long-term memory. For instance, carp are shown to become much wearier of fisherman and their lures once they have been caught. A carp that has been caught once and released is not likely to fall for the same trick again, displaying some level of recollection.

Some studies show that fish can retain certain pieces of info for months or even years, usually related to either their food or being eaten themselves. For instance, goldfish appear to be able to remember the color of feeding tubes for up to 1 year after the last sighting. Also, some catfish can remember food calls from human beings up to 5 years after they have heard it last while also being able to remember the voice of that specific human being.

Salmon are shown to be able to recall lights that signal feeding time up to 8 months after they have last seen the light. There is also the fact that some fish can form cognitive maps and learn complex spatial relationships, recalling them months or even years later.

The bottom line is that fish do have a certain level of memory, which does show signs that they are more intelligent than we first thought.

colorful cichlids swimming in tank
Image: andreibucataru.ro, Shutterstock

Fish & Tool Use

Another sign of intelligent life is when animals use tools to perform a certain job. It takes a certain amount of cognitive abilities to recognize those certain things when it comes to the use of tools:

  • An object requires a tool to manipulate
  • The recognition of a tool
  • The connection between the tool and the object for which the tool is to be used
  • The recognition of a problem and a solution

As you can see, it takes a fair bit of mental power to use tools. That being said, there are not too many examples of fish using tools. However, this is most likely because fish only have mouths and no fingers or thumbs and can therefore not pick tools up. Yet, there are still some examples of fishing using tools to perform certain jobs.

For instance, some fish have been known to hold oysters, clams, urchins, and other shelled animals in their mouths and smash them against rocks to get to the meaty inside. As well, some fish shoot spouts of water at insects sitting on plants or the water’s surface to immobilize them.

There have even been experiments where certain species of cod learned to pull a string for food to be dispensed. So no, fish are not brilliant when it comes to this kind of thing, but there are instances of tool use nonetheless.

Social Cooperation

Yet another aspect of fish that shows that they have a certain level of intelligence is the fact that they can work in teams to do various things. Being able to work in a team means being able to recognize your place in the team, as well as the fact that the team can do a better job than the individual.

It also means that fish know what the job of their teammates is. At any rate, there are various species of fish that are shown to work in teams, mainly to catch food, swimming in specifically coordinated patterns to achieve a certain end.

It is also shown that fish seem to be able to recognize individual fish to a certain degree. Some species can learn the behavior of other fish and may indeed be able to recognize a specific fish based on its behavior, attitude, and other things too. Some species of fish also seem to be able to learn from a leader, such as memorizing a specific route taken by a leader.

They can learn where dangers lurk, where there is lots of food and other such things from their fellow fish. While this doesn’t mean that a fish can do calculus and geometry, it does show that there is a certain level of intelligence.

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We did not cover everything there is to cover here, but there are some good examples above of how fish are probably not as dumb as we once thought. Admittedly, the proof that scientists have gathered can be interpreted in different ways, but there is a lot of evidence. At any rate, no, fish are not geniuses, but they definitely have brains, and when it comes to simple tasks, they can use them fairly well.

See Also: How Many Senses Do Fish Have?

Feature Image Credit: dien, Shutterstock

Lindsey Stanton Profile Picture

Authored by

Lindsey discovered her passion for fish keeping after a junior high school field trip to the Shedd Aquarium in Chicago. Prior to becoming Editor-in-Chief of It's a Fish Thing, Lindsey studied marine biology at the University of California-Santa Cruz. She loves goldfish, tetras, and mystery snails, and recently began experimenting with a saltwater aquarium.

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