How smart are fish and how do you recognize fish intelligence?

Fish are fascinating animals whose habits and behaviors can seem alien to us. Because they are very different from humans in behavior and appearance, it can be easy to assume that they lack intelligence. However, this is far from the truth. Fish have been studied for decades, and there is a wealth of scientific literature of their intelligence and cognitive abilities. In various tests of intelligence, fish have demonstrated that they are smart, resourceful, and uniquely suited to their aquatic environments.

How is fish intelligence measured?

Intelligence can be characterized in animals as a high degree of cognitive complexity, but applying measurements of intelligence across species can be tricky. A test that measures intelligence in a mammal, like a monkey, may not apply to fish or birds, but this does not mean that these species lack cognitive complexity. Thus, the challenge lies in devising tests of intelligence that are applicable across species.

Tests of intelligence that have been used in a variety of species, including fish, include problem-solving in unfamiliar contexts (often in laboratories), spatial learning, classical and operant conditioning, reversal learning, and social learning. Tool use, mathematical competency, memory, and self-recognition have also been tested in fish and are considered factors in measuring intelligence.

How to recognize fish intelligence

In addition to the challenges inherent in comparing intelligence across species, recognizing fish intelligence may be made harder because of a bias within the scientific community formed by longstanding but outdated assumptions about evolution. This bias assumes fish are lower than mammals on a linear evolutionary scale, with primates at the apex.

This dogma that mental and behavioral complexity increases the closer a species is to humans evolutionarily has dominated Western scientific thought, despite Darwin and earlier non-Western scholars offering an alternative view that species continuously co-evolve within their own specialized biological niches. As a result of assuming that fish are less evolved, both scientific investigators and the general public may have been slower to recognize cognitive complexity in fish. However, this has been changing over the past decade, with studies of fish intelligence significantly increasing between 2010 and 2019.

Fish intelligence has been recognized in several areas of study, including spatial navigation, numeracy, learning, decision-making, and theory of mind. Observations of fish in the wild have noted other cognitively complex behaviors like tool use.


Fish have been shown on many occasions to have excellent memories. One of the simpler tests of memory is time-place learning, whereby a species remembers a rewarding event and then returns to the place where the event occurred.

In fish, this has been demonstrated through hand-feeding them in ponds, for example. Fish in these situations quickly learned to wait for the feeding at the designated time and place — for some species time-place learning occurred within two weeks. For comparison, rats (another cognitively complex species), achieve time-place learning in about 19 days, and garden warblers master similarly complex memory tasks in about 11 days. Zebrafish have also shown the ability to form and retain short-term memories.

Fish also have impressive long-term memory capabilities. In numerous experiments, tiny rock-dwelling gobies remembered how to get back to their home pools when they were moved nearly 100 feet to another location. These small fish also remember locations of their home pools after being kept elsewhere for over a month.

Sharks have demonstrated memory retention of up to 50 weeks (the extent of the experiment), and African cichlids have retained memories for 12 days (again, the extent of the experiment). Both of which suggest their memory retention could last even longer.

Tool use

Several fish species have developed specialized tool use, another mark of cognitive complexity, while around 9,000 fish species have been documented using materials to build homes or nests.

The graphic tuskfish uses coral and rocks to break open shellfish to eat, while various species of wrasse use rocks to crack open invertebrate prey like sea urchins. Cichlids and catfish glue their eggs to leaves and rocks, and then use these items to carry their eggs when they are threatened. Archerfish use their mouths as squirt guns to remove prey from hiding places.


Fish use a variety of materials to construct homes and nests, and in fact, more fish species engage in such construction than mammals do. Some fish use materials produced by their own bodies, like the bubble nests of male gouramis and the mucus cocoons of wrasse.

Other species of fish demonstrate remarkable precision in the selection of construction materials, like cutlips minnows, who collect 300 pebbles of identical size to create mounds with consistent dimensions. The jawfish collects rocks to build intricate walls with openings just large enough for the fish to pass through. The rockmover wrasse builds a house of coral for sleeping in that is abandoned and constructed anew every day.

Social intelligence

Social intelligence, or social cognition, describes a complex set of skills pertaining to the ability to recognize, react to, and predict the behavior of others. Fish have demonstrated social intelligence in a variety of areas. Fish have the ability to recognize familiar individuals, to obtain information from fellow fish about mating choices, predator avoidance, and food sources, and to cooperate to acquire food and other benefits.


Some species of fish will engage in deception to fool those around them. This may include mimicry or camouflage to fool predators, or it may take place within complex social interactions. For example, Brachyhypopomus gauderio generate weak electric signals to communicate with one another. These signals can also communicate the size of the fish, and studies have found that smaller, skinnier fish will amplify their electrical signals to appear larger than they are, effectively deceiving their fellow fish.


There are many striking examples of cooperation in fish species, a highly complex social skill. In one example, certain species of fish will cooperate when surveying the presence of a predator, which enhances the likelihood of survival. And, if one of these fish fails to uphold their obligation, either by leaving or hanging back, the other fish will remember and refuse to work with them in the future.

Fish can even cooperate between species, as in the case of groupers and moray eels. Groupers signal to moray eels when they are ready to hunt for food, and the eel follows the grouper to the hunting location. Then, the eel swims among the coral while the grouper swims above. Both benefit from this relationship as prey escaping either above or below the coral are caught and consumed.


Numeracy refers to the ability to count numbers and differentiate between different quantities. Fish often exist in environments where greater numbers equal greater safety, so being able to differentiate large and small groups is key for survival in many species. Mosquito fish have demonstrated the ability to count up to five and have also shown an understanding of mathematical ratios.

Angelfish can also reliably count to five and use ratios to choose between larger groups, and cichlids and stingrays can perform basic addition and subtraction. Newborn guppies can count up to four, but seem to learn ratios later as they mature.

Social learning

Social learning is the ability to observe, model, and imitate others within a social group. Zebrafish have demonstrated this ability in experiments where untrained fish learned from previously trained fish which routes to follow to escape from trawl nets.

Mandarin fish learn novel feeding techniques from one another, and the tropical damselfish uses social learning to recognize predators.

Latent learning

Latent learning occurs when information is acquired without any reward or motivation attached to it. In this process, information is picked up subconsciously that will emerge later. Latent learning has been most heavily studied in zebrafish, who have shown the ability to remember a maze after being allowed to freely explore it.

Cleaner fish

Cleaner wrasse provide a unique service to larger fish by cleaning parasites and dead skin from their bodies. To perform this function, they exhibit complex social interactions with both the “client” fish and each other. Cleaners prefer to feed on mucus generated by the client fish, but feeding on this too soon during the interaction results in the client fish leaving.

Cleaner fish approach the client fish in pairs, and face a social dilemma: they must balance helping their partner with “cheating” to consume the desired mucus. Social pressure plays a role in ensuring good behavior — when there is a third fish observing them, cleaner fish tend to behave more cooperatively.

Cleaner fish can also differentiate between transient and local fish, prioritizing transient fish since local fish will stay in the area and be available later. If they accidentally bite a client fish during “service”, they have methods for reconciling with them, like giving them backrubs. Cleaner fish skills require them to navigate complex social interactions, read social skills, and differentiate between individual fishes.

Do fish recognize humans?

Fish have demonstrated the ability to recognize and differentiate between individual fish and different species of fish, but they can also recognize and remember human faces. Archerfish can tell the difference between individual human faces with a high degree of accuracy. Given how attuned they must be to details within their environment, it is likely that other species of fish are able to recognize familiar human faces.

What do fish think of humans?

Some researchers think fish can experience emotions arising from positive and negative experiences, such as fear, pain, and anticipation of events like receiving food. They also have the ability to form short- and long-term memories, and recognize when someone has treated them well or treated them badly. Given these capacities, it is likely that their interactions with humans are determined by whether they’ve had positive or negative experiences, or if they perceive humans as threats or food sources.

Despite their intelligence and potential capacity for experiencing positive and negative emotions, fish are some of the most heavily consumed animals worldwide. Since the 1960s, global fish production has quadrupled and people are eating twice as much fish. So many fish are slaughtered annually that they are measured in tons rather than individual fish, and in 2017 alone an estimated 51 to 167 billion farmed fish were slaughtered. Many of these fish are raised on factory farms, where they live in unnatural, stressful, and often crowded circumstances. According to the FAO, 424 species of aquatic animals were farmed worldwide in 2017.

Fish suffer not only from human consumption, but also from widely held public perceptions that they do not possess cognitive awareness or feel pain, despite scientific evidence to the contrary.

Are fish smarter than dogs?

Comparing intelligence across different species can lead to false assumptions, due to the fact that individual species have uniquely adapted to their environments and ways of living. However, research on blind Mexican cavefish found that they are able to create complex cognitive maps of their environment only hours after being added to an unfamiliar tank. They were also able to adjust their behavior when obstacles were added to their tanks, relying on learning and memory.

While a definitive determination cannot be made, fish have performed as well or better than dogs on some intelligence tests. In another example, Pavlovian training in dogs, in which a stimulus is given shortly before food is provided, can take around 20 trials before the association is made between the stimulus and the food. Wild rainbow fish learned the association in 14 trials.

What is the most intelligent species of fish?

Manta rays have the largest brain mass of any fish studied as well as extensive cerebellar foliation, a characteristic that may be associated with increased social and cognitive abilities. African mormyroid fishes also have large brain masses, with large cerebellums and extensive complexity observed in their brains. This may be due in part to a unique sensory system they have evolved.

Given that there are around 32,000 known species of fish existing in the world, and only a small fraction of these have been studied, it is difficult — and ill-advised — to assign a label of “most intelligent” to any one fish species. All fish species studied have demonstrated some level of cognitive complexity which indicates that popular perception of fish intelligence is wrong. .

Facts about fish intelligence

  • Some fish have lateralized brains like humans, which probably allows them to use their left and right hemispheres for different tasks, effectively multitasking.

  • Fish outperform monkeys, chimpanzees, and orangutans on some complex foraging tasks.

  • Fish have individual personalities and this can affect whether other members of the group will follow their leadership.

  • Fish are able to keep track of time and predict the timing of events.

  • The cleaner wrasse has passed the mirror mark test, a measurement of self-awareness in animals.

  • Sharks are not only able to differentiate shapes like squares, triangles, and rhomboids, but they are also able to identify when optical illusions are present.


Fish are among some of the most abused animals worldwide. They are raised on factory farms or caught from the wild and slaughtered for human consumption, often suffering agonizing deaths. They are the second most numerous animals used in cruel laboratory experiments, after mice, and their capacity for pain and intelligence is often denied. Yet scientific evidence shows that fish have complex and remarkable cognitive abilities and likely possess an acute awareness of themselves and their surroundings.

Fish are amazing animals who should be treated better by humans. One important way to acknowledge how smart fish are and honor their complexity is to stop eating them. Refusing to purchase products that contain fish, like certain beers, makeup products, and omega-3 supplements containing fish oil, will also help.