Do Fish Feel Pain? The Science Behind Fish Sentience

do fish feel pain

Humans kill more fish than they do any other vertebrate. At 2.7 trillion per year, the number of fish killed by humanity through fishing, farming, and pollution is truly incomprehensible. For many people, the mass killing of fish has always seemed more morally justifiable than that of other animals, and pescetarianism is a relatively common diet. This is likely because fish look and act so different to humans that they seem too strange—too distinct and distant—to be considered in any way like us. 

However, the evidence suggests that fish feel pain and suffer as a consequence of humanity’s actions. Although fish may not feel pain in the same way that we do, the psychological experience is nevertheless likely very similar. When one considers the sheer scale at which fish are being deliberately killed, on top of the thoughtless ways in which they are slaughtered or left to die, the suffering experienced by fish may be greater than that of any other group of sentient beings.

Do Fish Feel Pain?

The answer to the question of whether fish feel pain is a decisive “yes.” This has been established in a multitude of scientific studies evaluating different criteria. So, for example, fish bodies create natural opioids to suppress feelings of pain in their body and exhibit physical reactions when treated with painkillers. 

One intriguing study conducted by the University of Liverpool followed zebrafish. The zebrafish were given a choice of two tanks, one barren and one enriched with views of other fish and foliage. The zebrafish naturally chose the enriched tank. However, some of the fish were then injected with acid, whilst the barren tank was pumped full of pain killers. The fish injected with acid moved to the painkiller tank.

Scientists have reached a consensus on the issue of fish pain, concluding that their suffering is real. But even without mountains of supporting scientific data, it would make little sense if fish couldn’t feel pain. Pain is a physiological response to dangerous stimuli, which may threaten you with death, and fish seek to survive and pass on genetic material like all living things. They also have brains, central nervous systems, and all the receptors needed to feel pain. 

Do Fish Feel Pain When They Get Hooked?

The mechanism of pain occurs when a harmful stimulus interacts with a nociceptor on the body of an animal. The nociceptor then sends an electric signal to the brain, where the psychological experience of pain manifests. Fish have numerous nociceptors in their mouths and thus getting hooked is certainly a painful experience for them.

Do Fish Feel Pain When They Suffocate?

Fish certainly feel pain when they suffocate, which can be an incredibly drawn-out process. It can take some fish species over an hour to die from asphyxiation. This method of killing creates an intense stress reaction in fish; they flap, gasp, wriggle and flail during their prolonged period of death, accumulating lactic acid in their muscles and more rapidly bringing on rigor mortis, which all damages the quality of their flesh.

Yet it is likely the change in pressure when they are hoisted from the water into the air which causes them the most suffering. Fish are incredibly sensitive to changes in pressure and are indeed much more sensitive to pressure than other animals. The sides of a fish are so sensitive that they have been compared to the human cornea in their vulnerability to pressure.

This is because fish have a system of sense organs that spans the lengths of their body, called a lateral line system, which helps the animal understand changes in pressure and nearby movement in the surrounding water. The trauma of the rapid pressure change that occurs when a fish is pulled from the water into the air is surely immense, and trillions of fish are killed this way, through suffocation and exposure, each year.

Do Fish Feel Pain in the Same Way as Humans?

Whether or not fish feel pain in the same way humans do is a matter of debate. Those who want to deny fish pain, or portray it as irrelevant, have traditionally focused on the fact that fish lack a neocortex, the area of the brain where mammals process pain.

However, to dismiss the possibility of fish feeling pain based on their differing anatomy alone is far too reductive. Even if their pain is experienced in a different way, “different” doesn’t mean that the pain is less intense, or that it isn’t worth caring about. Intelligence, emotion, and experience seem to be exhibited by animals who bear very little resemblance to humans, as explored in documentaries like Netflix’s My Octopus Teacher. Seeing as fish behave in numerous ways which suggest pain, including responding to painkillers, creating their own painkillers, exhibiting markers of stress, and changing their behavior when exposed to damaging substances, it would be counterintuitive to discount their pain altogether. 

Octopuses are not fish, but they provide an interesting example of marine animal sentience.

Based on this evidence, it would appear that fish do feel pain similarly to humans after all. While one can debate exactly how fish subjectively experience pain since they are sensitive and sentient creatures it is perhaps best to err on the side of caution in choosing whether to promote their unnecessary suffering or leave them alone to live an uninterrupted and natural existence.

Scientific Investigation             

Argument by Analogy       

The argument by analogy is one of the best ways we have to evaluate the presence of pain in other creatures—not just fish, but all animals including other humans. Because pain is informed by a subjective and elusive psychological experience, scientists cannot measure it empirically. However, as most of us experience pain, and we see other people react to the stimuli, in the same way, we assume that they also experience pain. This can be extended to all animals; since humans, dogs, pigs, chickens, and fish will all exhibit the same markers of stress and pain, like hyperventilation, suspension of feeding, and reduced activity, then the most probable explanation is that they feel pain as we do.

How Do Fish Feel?              

Peripheral Nervous System

The peripheral nervous system is one of the primary means by which fish navigate their environments. There are many components of the peripheral system, and the lateral line organs, which can detect minute ripples in the water, are a key part. Fish also have eyesight comparable to that of humans, although their sense of taste is generally more important to them. Fish have taste buds on the outside as well as the inside of their mouths, which allows them to taste for hints of food, carried by currents in the water.

Nerve Fibres

Nerve fibres are the long parts of nerves that carry nerve impulses away from the cell body. More complex vertebrates like mammals tend to have more of a certain kind of fibre called “C fibres” related to pain, temperature, and itch than “A fibres” related to proprioception. Some have argued, on the basis that fish have few C fibres, that they are unlikely to feel pain at all. 

However, the predominance of A fibres in fish has been accounted for in studies that have examined changes in fish behavior due to a pain reaction. The fact that fish anatomy is different, and that pain may work in a different physiological way in their bodies, does not suggest that they do not experience pain. The idea of convergent evolution is relevant here, whereby an organism can evolve the same trait or faculty as another creature through a different chain of events. Fish biology is different from that of mammals, but they therefore likely feel pain through different systems, as has been generally accepted in the case of birds.


Fish have receptors, and specifically, nociceptors, which detect pain, all over their body. Different species are adapted to react to different stimuli. So, for example, the rainbow trout’s nociceptors are not responsive to water temperatures beneath 4 degrees Celsius. Particularly nociceptor-dense and thus sensitive parts of the fish are around the nostrils, eyes, the fleshy parts of the tail, and the pectoral and dorsal fins. The evidence for cartilaginous fishes’ ability to feel pain is less decisive, but they have been studied in far less detail than their bony relatives.

Central Nervous System   


Fish brains differ in some respects from mammalian brains. Most notably, fish do not possess a neocortex, which scientists once thought was central to the experience of pain. Some scientists maintain that because fish lack the swollen cortices typical of mammals, they cannot feel pain, but this perspective is becoming outdated.

There are two components to the experience of pain. The first is nociception, which is the ability of certain sensitive cells to detect noxious stimuli, which triggers a reflex reaction, moving the creature away from harm. This does not imply a psychological component. However, a mind with the necessary emotional capacity can interpret the nociception, resulting in the psychological experience of suffering.

Seeing as fish exhibit all the same physiological and neurological reactions to noxious stimuli that other sentient animals do, one would need to have a particularly strong reason to think that their brains are too simple to experience pain. The absence of the neocortex is insufficient to establish this, and science is progressively uncovering the way that consciousness and subjective experience are not solely a feature of mammal-type neurology. As the Cambridge Declaration on Consciousness, made by a group of leading neuroscientists in 2012, states: “The absence of a neocortex does not appear to preclude an organism from experiencing affective states.”

Effects of Analgesics

Effects of Morphine

Morphine is the most widely used analgesic (painkiller) in studies of fish pain. It is also the drug that is most strongly associated with positive reactions in fish, proven across several studies to reduce neurological and psychological stress in the fish it is administered to. It has been proven to be effective across different fish species, like rainbow trout, winter flounder, and goldfish.

Effects of Naloxone

Naloxone is a drug that reverses the effects of opioids like morphine. In studies where naloxone was administered to fish who had received opioids like morphine or buprenorphine the effects of the drug were inhibited or reversed, and nociception became active in the fish again. This further cements the fact that fish have a sensitive nervous system, whereby nociception causes a pain response in the brain which can be suppressed by painkillers and which returns if the painkillers are reversed.

Other Analgesics

There are a wide variety of other drugs used to treat fish pain in studies. The majority of these drugs have been found to have very little or no effect or to cause negative side effects, but most have been tested so infrequently that no firm conclusions about their effectiveness are available. It is also worth bearing in mind that fish are a highly diverse group of animals, and painkiller effectiveness will vary between species. More research into this area is needed.

Avoidance Learning

Fish have demonstrated avoidance learning, meaning that they can remember certain signals which suggest the presence of noxious stimuli and avoid them. In one study, a light was shone into a rainbow trout’s tank, ten seconds before a dip net was plunged in to frighten the fish. Over a five-day period, all thirteen fish from the study learned to flee once they saw the light, but before the net actually entered the tank. The authors argued that this demonstrated fear in fish and a higher level of sentience than had often been claimed.

Another study showed how fish could mediate their pain response, suggesting that they were reacting out of psychological pain and not pure reflex. Goldfish and rainbow trout demonstrated aversion to a part of the tank where they had received electric shocks. However, once another fish was introduced the first fish would move closer to the other fish, into areas of the tank they had previously avoided. Trout were willing to tolerate low-level shocks to be closer to the other fish, whereas without the presence of the second fish they would exhibit aversion to a low shock environment altogether.

Physiological Changes

When fish experience nociception the neurons across their brain light up in response, showing activity that likely corresponds with a subjective experience of pain. Fish also hyperventilate and exhibit high-stress behaviors associated with pain.

Protective Responses   

Fish exhibit a wide array of protective reactions to noxious stimuli. These include rubbing body parts that have been injected with acid as well as suspension of feeding and reduced activity.

Is Fishing Cruel?

The word “cruel” denotes actions that willfully cause pain to others and indifference to their suffering. When we consider this definition and mull on the fact that one does not have to eat fish, or any animal product, to have a nutritionally sufficient and delicious diet, it becomes much harder to justify fishing. Fishing causes unnecessary suffering, whereby people are willingly hurting animals when alternatives exist. As such, the word “cruel” seems a valid description.

Why Do People Believe That Fish Can’t Feel Pain?

Fish are hard to relate to as animals, so the concept of them experiencing pain may have been harder to conceive in the first place. They cannot vocalize suffering as mammals can, and humans have been catching fish for millennia. As far as the latter point goes, it has therefore always been inconvenient to suggest that fish, a source of food, may feel pain. Indeed, those animals more closely related to humans were long argued to be unfeeling automatons, an idea that justified the industrialized way animals are farmed and caught today.

The science establishing fish suffering is also relatively new. Nociceptors were only proven to exist in fish in 2002. Therefore, it is possible that the new consensus on the reality of fish pain has yet to come out. However, the waters have been muddied by a slew of articles and testimonies which continue to deny this fact, often drawn up by avid fishermen and those on the payroll of the fishing industry.

The Harms of Industrial Fishing

There may be parts of the world where people must fish to survive, in which case it would be justified. There is also no denying that the amount of suffering caused by a single sports fisherman is minuscule when compared to that of an industrial trawler, which may kill thousands and thousands of fish, not to mention seals, birds, dolphins, and turtles that get snagged in its nets.

Yet any time someone hurts an animal when they don’t need to, they are behaving cruelly. The oceans are being ransacked more and more ruthlessly, and fish continue to die in overwhelming numbers while no consideration is given to their welfare, often crushed beneath each other or left to suffocate for hours. The fact that these are complex, sensitive, and sentient creatures who have their own, equally real experience of pain is a fact well worth dwelling on.