Fish are widely seen as less worthy of moral consideration than mammals and birds. As a result, they are often overlooked in conversations about animal welfare. But a growing body of scientific research is making humanity’s lack of concern for fish—who are killed for food in higher numbers than any other vertebrate—increasingly difficult to justify.
Do fish feel pain when hooked?
In a study of pain perception in fish, rainbow trout whose lips had been injected with either acetic acid or bee venom (both of which cause pain in humans) showed signs of discomfort.1 The researchers found that these animals have multiple pain receptors (called nociceptors) around the mouth and head. Another researcher notes,
“Contemporary studies over the last 10 years have demonstrated that bony fish possess nociceptors that are similar to those in mammals; that they demonstrate pain-related changes in physiology and behavior that are reduced by painkillers … The neurophysiological basis of nociception or pain in fish is demonstrably similar to that in mammals.”2
Fish produce the same opioids in response to apparently painful stimulation that mammals do. As noted in a Smithsonian magazine article summarizing contemporary research, a fish’s
“brain activity during injury is analogous to that in terrestrial vertebrates: sticking a pin into goldfish or rainbow trout, just behind their gills, stimulates nociceptors and a cascade of electrical activity that surges toward brain regions essential for conscious sensory perceptions (such as the cerebellum, tectum, and telencephalon), not just the hindbrain and brainstem, which are responsible for reflexes and impulses.”3
Based on this, we can be reasonably confident that fish feel pain when hooked. They also likely suffer from fear and stress.
Some methods of hook and line fishing have the potential to cause fish (and any non-target animals who happen to get caught) more pain and fear than others. While a fish caught by an individual angler can be reeled in and killed or released within a relatively short space of time, fish caught by a longline set that stretches for miles and has thousands of baited hooks might be left hooked for hours or even days, putting them at risk of further injury and distress.4
Do fish feel pain when they suffocate?
In short, yes. Suffocation (also known as asphyxiation) is thought to be one of the slowest, most painful ways for fish to die. In one study, carp stayed alive for as long as five hours after being taken out of the water.5 The study’s authors wrote that this way of killing “is inhumane and substantially affects fish welfare.” Despite this, it’s common practice onboard commercial fishing vessels to leave fish to suffocate on deck.
Evidence that fish experience pain
Proving that fish—or any other animals—experience pain is far from straightforward. Researchers not only have to prove that their test subjects can sense and react to potentially painful events, but also that any physiological and behavioral responses to such events are more than just reflexes.6For this reason, researchers developed a set of 17 main criteria for pain perception in animals.7 Of these, just one—a behavior known as relief learning—is still yet to be observed in fish.
The science is clear that fish have the necessary biological framework for sensing pain, and the complex ways in which they respond to harm make it very difficult to deny that these animals are capable of suffering.
Although the fish brain is structurally different from the human brain, research shows that it has the capacity to sense and process pain. Exposing fish to potentially painful stimuli, such as being pricked with a pin,1 “has been found to trigger brain activity outside of the areas that are responsible for automatic, unconscious reactions.9
Research suggests that parts of the fish brain function in a similar way to the amygdala and hippocampus, which process feelings and emotions in mammals. Which areas of the brain a fish uses to react to fear and pain may differ between species.10
Fish are also far more intelligent than many people realize. Research has shown that some fish species have advanced cognitive abilities such as problem-solving, tool use, self-recognition, cooperation, and long-term memory.11In one experiment, adult cleaner wrasse fish outperformed capuchin monkeys, chimpanzees, and orangutans.12
Central nervous system
In humans, the brain is joined to the spinal cord. These two components make up the central nervous system (CNS), which controls movement, breathing, and other important functions. The CNS is also responsible for taking in, processing, and reacting to sensory information. The same is true in fish, who have all of the brain areas that mammals use for the central nervous system processing of pain.13
Nerve fibers play a key role in sending pain signals to the central nervous system for processing. Fish have two types of nerve fibers: A-delta fibers, which are associated with immediate pains, and C fibers, which are associated with dull aches and persistent pain. Research suggests that A-delta fibers are the predominant type of pain-related nerve fibers found in fish, but that these may operate in a similar way to how C fibers operate in mammals.14 The existence of both types of fibers suggests at a bare minimum that, like mammals, fish can experience a variety of types of pain.
In humans, the opioid system regulates feelings such as pain and pleasure. It may also play a role in decision-making.15 The complex opioid system that fish have is so similar to ours that zebrafish are used as models for researching opioid addiction.16
Opioid receptors—which are activated by both endogenous opioids (natural substances released by the brain) and opioid drugs such as morphine—can be found in the fish nervous system.17 This would make little sense if fish weren’t capable of feeling pain.
Peripheral nervous system
Further evidence of pain in fish is that they have a peripheral nervous system.18 As in mammals, this is made up of a complex network of nerves that connect the central nervous system to the rest of the body.
Research shows that fish can change their behavior after experiencing pain in order to ease the pain or protect themselves from further harm. In one experiment, zebrafish who were injected with acetic acid chose to spend time in a barren chamber with pain relief over their usual choice of a chamber enriched with gravel and plants. In another study, goldfish went without food for three days after receiving an electric shock in the area of the tank where they were fed, demonstrating that they associated the electric shock with an unpleasant sensation and wanted to avoid it.19
Pain receptors, or nociceptors, are a type of neuron that help to protect the body from injury by detecting and alerting the brain to harmful chemicals, high levels of pressure, and extreme temperatures. These receptors are what trigger the reflex reaction that makes you automatically pull away if you touch something sharp or hot. Evidence of nociceptors in fish was one of the first signs that they may be capable of pain perception.20
How do fish react to pain?
Fish react to pain in a variety of ways, some of which are similar to how humans and other animals might behave when ill or injured. In research experiments, fish who were injected with harmful substances have been observed to breathe faster than normal, swim around less, go without food, rock from side to side, and rub the injection site against their tank.21 Such changes in behavior tend to subside when the fish are given painkillers.
Do fish feel pain in the same way as humans?
The fact that nonhuman animals can’t describe how they feel makes it very difficult, if not impossible, to get a clear picture of how fish experience pain.22 Studies suggest that there may be some differences between how fish feel pain and how humans feel it, but this doesn’t necessarily mean that a fish’s experience of pain is any less real. According to fish welfare scientist Dr. Lynne Sneddon, research has “shown that the physiology, neurobiology, molecular biology and brain activity that many fish species show in response to painful stimuli is comparable to mammals.”
Why do people believe that fish don’t feel pain?
The belief that fish don’t feel pain is often based on an assumption that they lack the capacity to do so. Many people see fish as simple-minded animals who exist for the sole purpose of being eaten. Thankfully though, this point of view is becoming less mainstream as people begin to realize that there’s more to fish than previously thought.
In a 2016 essay, neuroscientist Brian Key argued that because fish do not have the same brain structure as we do, they “lack the neural architecture for feeling pain.”23 The essay prompted multiple responses from other scientists, many of whom pointed out that it is illogical to assume that a human-like brain structure is needed for pain perception in nonhuman animals.24
It may be the case that some people dispute the evidence of pain perception in fish because of the costs of acknowledging it. If fish were to be afforded the same welfare protections as other animals (even though most of these are woefully lacking), the global fishing industry would, in theory, have to make significant changes to how fish are caught and killed.
Is fishing cruel?
The welfare of the hundreds of billions of fish who are captured in the wild each year is largely ignored. Most common fishing methods—including trawling, purse seining, gill netting, and trolling—cause a huge amount of pain, fear, injury, and distress to fish and other wild animals. With this in mind, it seems clear that commercial fishing is one of the biggest causes of animal suffering worldwide.
Aquaculture is no better. Fish farms have many of the same characteristics as land-based factory farms: overcrowding, poor welfare, unsanitary conditions, and routine antibiotic misuse. And, contrary to popular belief, rearing fish in captivity does very little to solve the problem of industrial fishing. Estimates suggest that up to 120 small fish may be taken from the wild to feed just one farmed salmon.
A very small number of fish producers are beginning to adopt higher welfare methods of capture, farming, or slaughter, but for the overwhelming number of fish destined for human consumption, the situation remains bleak. Despite the fact that fish is often promoted as a better choice than other meat products, the reality is that the vast majority of fish products on the shelves are neither ethical nor sustainable.
Fish are sensitive animals with rich social lives. They are capable of experiencing pain, and as a result, they suffer immensely at the hands of the commercial fishing industry. The good news is that our individual food choices can make a positive difference. One of the best actions anyone can take to reduce animal suffering is to eat conscientiously—as few animals as possible, ideally none.