Fish Brain Anatomy & Function

Compared to the familiar shape and form of a mammal brain, the fish brain is rather odd looking.  It is elongated, has distinct sections, and is much smaller that a mammal’s brain in relation to its body.  However, it does everything a fish needs it to do.


At the front are the smell detectors, technically known as the olfactory lobes.  They are directly connected to the fish’s nostrils by the olfactory nerves.  The information processed in the olfactory lobes is passed to the telencephalon, which “understand” what the smells are.

Together the olfactory bulbs and the telencephalon are known as the forebrain.

Research has also indicated that the forebrain may play a part in learning and retaining automatic responses to things that are unpleasant, and also in spatial awareness.  One experiment found that goldfish with damaged forebrains were less successful at memorizing a maze.

Finally, some fish make noises, and this is also thought to be controlled by the forebrain.


The midbrain (aka mesencephalon) sits directly behind, and is connected to the forebrain.  It’s main purpose is to process and understand the signals sent from the fish’s eyes to the brain.  It is responsible for sight.  In fish that hunt by sight, this part of the brain is comparatively larger.

Other functions of the midbrain include learning and controlling muscular reactions.

Fish are also thought to be able to tell what direction a sound comes from by using the midbrain.  (Fish have bones in the skull that form an inner ear).


The hindbrain (aka metencephalon) is mostly responsible for controlling swimming, including the actions of the swim bladder.  It decides how much work a muscle does, how fast it works, and works out the balance of the fish.  Overall, the hindbrain controls what direction the fish swims.

Although the hindbrain is the largest part of the brain in most fish, those that swim fast and hard have the largest of all.  Fish that spend most of their lives latched on to rocks or other fish don’t have a large hindbrain.

Another function of the hindbrain is to detect chemicals that have an effect on blood sugar levels.


There are several other smaller structures in the fish brain that control functions relating to hormones, breathing, salt intake, signals from the lateral line and reacting to all the other organs in the fish, and stimuli it will encounter.

3 Responses to “Fish Brain Anatomy & Function”

  1. Jerry Kabiri Says:

    So what is the function of the Di-encephalon and Myencephalon

  2. Zachary Stoker Says:

    So which parts of the brain contribute to the fishes learning comprehension, fish aren’t as dumb as people think, and i’m doing a school project for a thing called “PBL” which means “Project Based Learning” thanks- Zac

  3. Joan Watters Says:

    Hi Zachary. I was listening to a local talk show and the question Do Fish Think? , was posed.” Mr. Know It all”, replied that the only thought a fish has is in it’s quest for food. “Is it edible or not!” This annoyed me to no end as I have a pet fish that has displayed the ability to think in several areas and will offer you some proof of my statement by providing you with a detailed description of my reason for coming to this conclusion. Then you can decide for yourself if my suspicions have merit. Let me know if you are interested and good luck with your project.

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