Do Fish Have Brain? Anatomy & Studies

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Yes, fish have brains. Okay, thanks for coming by, see you in the next article. Fortunately, you’re here to find as much as you can about the fish brain, so let’s get into that!

Anatomical Examination of Fish Brains

The fish’s brain is a more complex organ than we give it credit for and consists of 3 main sections:

  1. Forebrain (telencephalon) – This is the largest section that comprises olfactory lobes and the main cerebral hemispheres. The forebrain is responsible for the fish’s main cognitive abilities, including memory, decision-making, and learning as the primary functions. The olfactory lobes simply manage the fish’s ability to use its sense of smell to navigate its environment.
  2. Midbrain (mesencephalon) – This section is in control of the visual input and movement coordination. The midbrain allows the fish to react to outside visual, auditive, and other sensory inputs in real-time.
  3. Hindbrain (metencephalon) – The hindbrain controls automatic biological processes like breathing and heart rate, as well as basic instincts like fear, caution, instinctive movements, etc. This brain section contains the medulla oblongata, which regulates various physiological and biological processes, especially concerning organ functioning.

It’s worth noting that the fish’s brain is still subject to investigation and research, given that there are a lot of gaps worth exploring.

This is especially important, knowing that the brain’s amazing structure, complexity, and functioning while varying drastically between different animal species, share a variety of similarities across the board.

That’s because all animals on Earth have a common ancestor, which means that they’re all related.

For instance, mammals have the most complex brains on the planet, especially thanks to the limbic system, allowing for more complex emotions and motivations.

Reptiles and birds also have different brains that may not be as complex but are equally fascinating, especially since they have evolved differently. For instance, a hawk’s brain is entirely different than that of a human.

Birds of prey have more of their brain’s matter and neuronal activity dedicated to sight enhancement, so they can see better.

Cognitive Abilities in Fish

The standard so far has been that fish have very basic and simplistic cognitive abilities as part of a rudimentary cerebral activity.

We now know that that’s not the case. In reality, fish are quite complex in this department, being capable of expressing a multitude of advanced cognitive abilities.

These include:

  • Predator evasion tactics – Fish don’t just react instinctively to predators. Some do, but overall, fish have evolved and adapted to the presence of predators so they can improve their survival chances. Some fish have evolved camouflaging abilities, allowing them to blend with the underwater soil and the surrounding ecosystem. Others, like clownfish, rely on their symbiotic relationship with anemones to find protection from predators.
  • Decision-making – Fish can decide between various options, depending on their environment, social development, and the species’ specifics. They don’t just function automatically, as it was previously thought, but make active decisions based on what happens around them. In this sense, fish can decide to flee from a predator instead of keep eating, even if they’re hungry. Or eat despite being tired and wanting to sleep.
  • Problem-solving abilities – Most fish species exhibit impressive problem-solving abilities based on the situation. They can map their ecosystem to find the fastest escape routes when attacked, use tools to kill shelled animals like clams, and even memorize their territory based on the available landmarks. 
  • Learning abilities – Fish can also learn throughout their lives and adjust their behavior accordingly. They’re not born with a set knowledge system but instead a malleable one, subject to change and improvement over time.
  • Good memory – Fish also have good short-term and long-term memory and the ability to allocate information to a specific section based on its importance. This allows the fish to use past experiences to regulate their future behavior. In this sense, most fish species can recognize other fish, remember the best feeding places, remember the most dangerous areas where predators lurk around and navigate their environment more effectively.

As you can see, fish are by no means rudimentary in terms of brain capacity.

Evolutionary Significance of Fish Brains

We have several areas to dissect here, so brace yourself:

How Fish Brains Have Adapted to the Environment Over Time

The brain is a malleable organ that evolves and changes itself based on the input it gets from the environment. For instance, some fish have developed larger eyes with wider retinas to see better in the dark.

That’s because they live in habitats with low lighting conditions. Social species have developed social behaviors like recognizing those belonging to the same species. 

Fish can also differentiate between different sexes based on looks and scent. Other species have so-called lateral line systems, which allow them to detect changes in water pressure and vibration.

Sharks, for instance, can detect their prey’s heartbeats by sensing the faint electrical signals they give away. They can also sense one drop of blood among 1 million drops of water, allowing them to chase wounded animals with astounding precision.

Differences Between Levels of Complexity in Different Species

Not all fish are equal in terms of brain complexity and potential. The main differences between different fish species are due to environmental factors such as:

  • The difficulty of finding and accessing food
  • The number of predators in the ecosystem and their behavior
  • The various challenges that require problem-solving abilities and behavioral malleability

Based on these factors, fish vary drastically in terms of brain activity and complexity. As a general rule, social fish generally have more complex brains, and so do those that live in more demanding ecosystems.

This variation in brain complexity has allowed some species to form well-defined hierarchies, use tools to access food, and rely on complex behaviors to hunt and evade predators.

Benefits for Survival in Different Environments

The brain’s fascinating adaptability and complexity make it a unique organ with unique abilities.

This becomes more evident when assessing fish’s adaptability to wildly different environments, such as:

  • Some fish possess a labyrinth organ to allow them to breathe atmospheric air in low-oxygen waters
  • Some fish can alter their metabolic rates to enter a dormant state when food isn’t available (metabolic depression)
  • Morphological adaptations refer to fish developing specific body sizes, shapes, and colors to meet their environmental requirements
  • Behavioral adaptations refer to mating rituals, feeding habits, and migration patterns
  • Modified swim bladders are also present in some species that live in poorly oxygenated waters; the modified organ allows the fish to extract oxygen more effectively

There are numerous examples in this sense, which stand as proof of the brain’s amazing adaptability.

That’s because, yes, all of these physiological, morphological, and behavioral changes are instructed by the brain.

Role in Behavior and Communication in Fish

The brain plays a defining role in the fish’s ability to communicate its intentions. It also influences the animal’s behavior based on the environment and social connections.

Fish use a variety of cues to communicate with others of their own species. These include pheromones, coloration, movement, body posturing, and even vocalizations.

They also use similar cues to intimidate predators. Pufferfish inflate their bodies to make themselves appear larger.

The same behavior prevents the potential predator from swallowing the, now, larger prey that also contains venomous spines on top of everything else.

All these adaptations stand proof of the brain’s ability to influence the fish’s behavior and thought process.

Changes in Fish Brain Thanks to Domestication and the Species’ Adaptation to Captivity

Many fish have adapted to life in captivity better than others. Others haven’t adapted at all. This isn’t anything special because all animals fit this classification. What is special, though, is the observation that refers to the fish’s brain modifications due to their captive lifestyle.

The wild vs. captive-bred tilapia is the perfect example of this. Research has shown that captive-bred tilapias have larger brains compared to wild specimens, leading to enhanced cognitive and behavioral adaptations.

This leads captive-bred tilapias to be less shy and more aggressive than wild ones.

Captive-bred fish can also exhibit differences in lifespan, growth rate, maximum size, coloration, and behavior compared to their wild counterparts.

All of these differences are the result of selective breeding that forces the brain to promote specific traits. This process also allows some fish to recognize their handlers and associate them with food, whereas wild fish associate humans with danger.

Experiments and Research on Fish Brains

There have been numerous studies performed on fish brains aiming to understand the central nervous system’s functioning, adaptability, and structure. These include:

Studies on the neural basis of behavior – Using electrophysiology and imaging to assess the brain’s ability to inform behaviors like social interactions, swimming, hunting, predator evasion, etc.

Studies on cognitive abilities – Assessing the fish’s cognitive abilities that tap into social behaviors, problem-solving skills, and memory tasks. According to some of the studies, several fish species exhibit advanced cognitive abilities that include tool use and self-control.

Studies on the environmental impact of the fish brain – Assessing how the environment can influence the fish brain’s development, structure, and adaptation. These studies aim to provide a deeper insight into the fish’s adaptability to their ever-changing environments that humans can use to protect endangered species.

Studies on the genetic basis – Researching the impact of specific genes on the brain’s development and function.

Studies of the domestication effect on fish brains – How life in captivity can alter the brain’s functioning, influencing the fish’s lifestyle, behavior, and, ultimately, survival and adaptation potential. [1][2]


Fish are undoubtedly fascinating animals with more complex brains and behaviors than was previously thought.

Think about this next time you catch your fish watching you from the other side of the aquarium’s wall.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.

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