Do All Fish Have a Brain?

Do All Fish Have a Brain?

This is a question that seems to have an obvious answer, which is yes, fish do have a brain. One example would be to look at aquarium fish and how, when you walk into the room they swim to the top of the tank and appear to be looking at you. This is because they associate you with food. If a fish did not have a brain, they would not be able to associate you with food. Now that we have established that a fish has a brain, just how intelligent is a fish.

How Intelligent is a Fish

The basic definition of intelligence is a process of acquiring, retrieving, storing in memory, comparing, combining, and using new contexts for conceptual skills and information. The question is, are fish capable of doing that with their brains. In a way they do because when you add a new fish, for example, to an aquarium, the first thing they will do is being wary in their new surroundings until it becomes familiar to them. They will take their time to investigate their new home until they are satisfied it is safe, especially if there are other fish in the tank they are not used too. Seeing how they act in this type of situation shows that fish do have some degree of intelligence.

Cephalopods, which include squid and octopus, have well-developed brains. Evidence points out that the cerebellum part of their brain is capable of learning and growing, and performing functions that are important to all animals. Although there is no factual data on this some fishermen feel that certain carp that have been caught in a confined pond learn very quickly how not to get caught again after they are released back into the pond. The fishermen feel that this happens because the carp becomes aware of the bait that is being used, but it has not been proven or disproven. 

They have also studied the paradise fish and have proven that they will avoid any place where they have experienced an attack by a predator. They will avoid this area for months. This just proves that fish is capable of retaining information. The Archerfish will squirt jets of water at insects on plants just to knock them in the water so they can eat them. They have also learned that they can adjust the size of the squirts to the size of the insects along with learning how to shoot at moving targets.

In a laboratory study, the intelligence of the Atlantic cod was tested by being given access to an automatic feeding machine. In order to get food, the cod had to pull a string to release it. It did not take them long to figure out how to pull the string and get the food. Some egg-laying fish have learned to clean the surface where they are going to lay their eggs. They have also used GPS tracking to prove that fish have the ability to form cognitive maps so they are capable of navigating through oceans.

How is the Brain Size of a Fish Measured? 

Their brain size is measured in comparison to body size and weight. Some fish do break this rule. The most notable two are the shark and mormyrid. The mormyrid is any of several species of slimy, freshwater African fishes. They are soft-rayed, bony fish with a small mouth and eyes, forked tail fins, and abdominal pelvic fins. Both of these, when compared to their body weight, have massive brains. 

How Big is the Brain of a Fish?

Typically a fish has a small brain when you compare it to its body size. When comparing their brains to that of a small mammal or a bird, it is about a fifteenth of the size. In the mormyrid, their brain is about 3.1% of their total body mass; a human’s brain is only 2% of their body mass. The actual size of their brain is hard to say because there are different sizes of fish so their brains, in regards to size, have to adapt and adjust to the size of the fish’s skull. 

Interesting Facts About How Fish Use Their Brains

  • A goldfish appears to be able to remember the color of their feeding tubs for up to one year after last seeing them
  • Some catfish can remember food calls from humans up to five years after hearing it the last time.
  • Salmon can recall lights that signal feeding time up to eight months after last seeing the light
  • Salmon remember how to get back to their spawning site
  • The brain of a mormyrid uses about 60% of all the oxygen they consume while most will only use 2%-8% of the total oxygen they consume
  • Neither jellyfish or starfish has brains but they are not really a fish


According to studies and research, some feel that fish are more intelligent than some people think. Some fish have a larger brain than some primates in comparison to their body mass. One example is the elephant nose fish that has the largest brain-to-body weight ratios of all known vertebrates. As you can see, fish are intelligent and know how to use their brains. If they did not have a brain, they would not be able to do half of the stuff that they do. They would be like the jellyfish; they not only do not have a brain but also no bones and no heart.

Some fish use their brain to show some signs of mental life, especially in long and short term memory. The carp mentioned earlier in the article is a prime example of using their brain’s memory to keep them from getting into the same life-changing situation. Yes, fish is not a genius but they do have brains and they can use them when it comes to doing simple tasks and remembering certain tasks. A fish also has a long memory span, which has been proven many times.

So the answer to the question is yes, fish do have a brain and they know how to use it.

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