Do Fish Have Brains?

Yes, fish have brains, and they depend on them for survival (much like human beings) and other physiological processes. Their brain to body ratio is much smaller compared to most other vertebrates. There’s no exact brain mass for fish because it varies with the species.

Fish don’t just have brains; some species can be much more intelligent than dogs. In fact, Pavlovian studies have shown that a dog learns an association after 20 trials. But the wild rainbow fish learned in 14 trials – over the course of 7 days!

Though fish have a bad reputation for having a poor brain, there are so many interesting things to know. To learn more about it, let’s dive deeper into its functions.

How does a fish brain work?

The brain of fish has a similar function to that of other vertebrates. The fish’s senses – sight and smell – help it receive signals from its environment. The sensory signals are then sent to the central nervous system and brain through the nerves.

The brain creates appropriate responses to every situation. These responses are sent to specific body parts of the fish through motor neurons.

The fish brain monitors the conditions outside (i.e., deciphering signals from their environment) within the fish body (i.e., maintaining homeostasis), which is ultimately vital for their survival.

What is the difference between a fish brain and a mammal brain?

Unlike mammals, fish brains don’t contain distinct deep cerebellar nuclei. Instead of this feature, fish have a completely different type of cell in their cerebellar cortex, which is the primary target of Purkinje cells.

What is the difference between a fish brain and an invertebrate brain?

Fish have a centralized system of a complex brain structure with a spinal cord and nerves. Invertebrates lack this centralized structure and depend on a scattered chain of neural networks, which is much simpler.

Now, if you’re eager about the details of the fish brain, let’s know about it.

What is the anatomy of a fish brain?

Fish brains, despite their size, have multiple detailed parts. The fish’s spinal cord and brain together form the central nervous system and the web of nerves throughout the fish’s peripheral nervous system.

What does a fish brain comprise of?

In fact, there are four different components of the fish brain as follows:

1. Telencephalon

This is the front part of the fish brain that’s responsible for its smell-detecting senses or olfactory components.

It also comprises the cerebrum of the fish, which assists in the entire olfactory process. Fishes that have a sharp sense of smell often have a bigger telencephalon.

2. Diencephalon

This portion of the fish’s brain is right behind the telencephalon. The diencephalon is inside the brain – it is not visible from the outside if you take out the intact fish brain.

The fish brain section helps the fish conduct proper homeostasis (i.e. the capability of the fish to maintain an equilibrium within its body using physiological processes).

The brain region contains other important components like the following:

  • Thalamus: It sends sensory signals to the telencephalon.
  • Hypothalamus: This regulates the reproductive functions of the fish. It works by releasing neurohormones, which in turn control the synthesis and release of FSH and LH hormones.
  • Pineal body: It helps the fish identify light and darkness.
  • Saccus vasculosus: It is a seasonal sensor that helps the fish detect seasons and know when to breed, migrate, and undertake other actions. However, many say its complete function is yet to be known.

Most of these components/structures either help transfer received messages from the exterior to the relevant brain part or secrete hormones.

3. Mesencephalon or Midbrain

This part of the fish brain is located right over the diencephalon and helps in deciphering visual signs.

The region has a few zones – superficial white zone, deep white zone, central zone, and periventricular grey zone.

4. Hindbrain

This region of the brain consists of:

  • Brain stem: It connects the spinal cord with the brain, which helps in coordinating sensory information.
  • Cerebellum: This assists the fish in maintaining equilibrium.

As you see, a fish brain contains all the regions that you see in a human brain. But the only difference between the two species is the size of the brain compared to the body. The fish brain is much smaller compared to their body size, unlike other vertebrates.

Fish mainly need senses of sight and smell to function properly in daily life. So, its brain components mainly revolve around those purposes.

But fish brains lack a developed cerebral cortex (unlike human beings and primates), which helps in complex thinking.

How do you identify the brain of a fish?

Do fish have brains? Anotomy of a fish

Just like in human beings, the brain of a fish is also located within its skull. There, the spinal cord of the fish connects with the fish brain right at the skull base.

Though the fish brain is much smaller than the human brain, its weight and size are about 1/15th of a bird or small mammal’s brain-to-body ratio.

Bigger fish, like sharks, have an equal brain-to-body ratio to that of small mammals or average-sized birds.

So, the size varies a lot, and you can’t follow a specific formula to know a fish’s brain size or weight based on its body.

What are the Signs of Intelligence in fish?

With such a complex nervous system, fish can also be perceived as intelligent beings. They learn from their personal experience and the experiences of other fishes around them.

This is popularly known as observational learning, social learning, or cultural transmission.

So, let’s learn about fish intelligence with some examples.

1. Memory Retention

Contrary to popular belief, fish can retain long-term memory. For instance, some goldfish can remember the color of their food dispenser. Even after not seeing it for a year, it still responds to it.

Experiments show that common rudds, European chubs, and archerfish can recognize their owner’s face.

2. Sociability, Playing, Cooperation, and Communication

Two male Siamese fighting fish were set to fight in the presence of a female fish. Then, a new female fish is introduced to the tank.

The winner courts and socializes with both females. The first female sticks to the winner. But, the loser socializes and courts the new female only.

Fish use low-frequency sounds and body language to communicate and seek cooperation.

For instance, roving coral grouper uses a head-shaking sign to seek the slender giant moray to poke at small prey hidden in crevices. When the prey comes out, the grouper eats them.

White-spotted cichlids are observed to play by hitting floating thermometers to make them bob.

3. Cleaning, Tools, and Construction

Bluestreak cleaner wrasse is known to remove and eat bigger species’ ectoparasites.

Some wrasse species secure mussels, other bivalves, and sea urchins in their mouths. Then they hit it against a rock to break the shells open and consume the contents. They use their mouth and rock as tools.

In terms of construction, smallmouth bass, Pacific salmon, and bowfin dig to construct nests and burrows.

4. Deception Skills

Some fish species have learned the skill of deceiving others.

For instance, the male threespine sticklebacks distract predators that try to intrude on their nesting area or eat their eggs. The male pokes the ground and intruders feel that the nest is found there and leave the actual nest.

5. Food stocking

Species like climbing perch are known to stock food in its mouth. When starved for a day, they double the stocked food. They can adapt accordingly based on food availability.

Do all fish have same brain capacity?

Not all species have the same brain capacity or intelligence. Depending on these differences, life experiences and even expectancy differ for each species. So, let’s know about…

Which is the Most Intelligent Fish on earth?

Manta rays have the highest brain-to-body ratio out of all other fishes, which makes them the smartest studied fish. In fact, manta rays have bigger brains than whale sharks.

They have problem-solving, communication, and learning skills. According to the University of Colorado 2016 study, manta rays are found to identify their own image in the mirror as their reflection and not another specimen, which proves their self-awareness.

Which is the the Least Intelligent Fish on earth?

The bony-eared assfish are perceived as the least intelligent fish because of their bare minimum brain-to-body ratio compared to other studied fish and vertebrates.

This cusk-eel species has no bone mass and inhabits the deep ocean where food is limited. It lacks minimum thinking capabilities, which leads to its inadequate survival instincts.

A word from FishInAquarium

Fish are neither forgetful nor dim-witted. Rather, so many species have been able to survive in the wild solely because of their intricate brains. Next time you see a fish in a home aquarium or elsewhere, observe its behavior. You’ll definitely see signs of its intellect.

Now, if this article satisfies your queries about their brain, make sure to share it with other enthusiasts in your circle. In fact, you can also bring it up in a conversation when someone says, “Pardon my fish brain!” 😉

If you have any more questions, drop us an email, and we’ll sort things out!

Minnie B Miller - Professional aquarist and owner of FishInAquarium

About Minnie B Miller

Minnie B. Miller, a professional aquarist and owner of FishInAquarium, has over 8 years of expertise in fish breeding and care, gained through her roles at AquaticTX and Sea Lion Landing. Having honed her skills with various aquatic species, she is dedicated to empowering fellow enthusiasts by sharing her knowledge and experience.