Do fish feel pain?

The objection

“Fish are basically swimming reflexes. No real brain, no pain, they don’t feel a thing on the hook or the deck.”

The answer

Nobody can ask a fish what it feels, and the objection is right that a reflex can pull an animal away from damage with no feeling behind it. Scientists face the same problem with every animal that can’t speak, so they test for pain by its signs: nerve endings that detect injury, and changes in behaviour that outlast a reflex, compete with other needs and are prevented by painkillers. Fish have shown all of these in experiments since 2003, and Lynne Sneddon, who led the 2003 trout study described below, concluded in a 2019 review that it is highly likely fish experience pain [3].

How do we know fish feel pain?

Fish show the same signs that are accepted as evidence of pain in mammals and birds. In 2003, Sneddon and colleagues at the Roslin Institute in Scotland found nociceptors, the nerve endings that detect tissue damage, on the heads of rainbow trout; they responded to pressure, heat above 40°C and acetic acid, with properties similar to those of mammals and birds [1]. Trout given an acid injection in the lips breathed faster, took longer to start feeding again and behaved abnormally [1]. That work and later studies, reviewed by Sneddon in 2015, found that acid-injected trout avoided food for up to 3 hours, while those given a harmless saline injection, or the acid plus a painkiller, ate again after 80 minutes [2]. They also recorded trout and carp rocking on the bottom of the tank, and trout and goldfish rubbing the injection site [2]. The opioid system, the body’s own pain relief, is very similar in fish and mammals, and morphine prevents the drop in activity that a painful injection causes in trout and zebrafish [3].

Pain also pushes other concerns aside. Trout in pain ignore a new object they would normally avoid, and once given morphine they avoid it again [2]. Fish will pay a cost to escape pain or relieve it: goldfish given an electric shock in the part of the tank where they were fed stayed away for 3 days before hunger won [3], and zebrafish given a painful treatment gave up the dimmer, enriched chamber they normally preferred for a bare, brightly lit one once a painkiller, lidocaine, was dissolved in its water [2]. Sneddon’s 2015 review concluded that teleost fish, the group trout, carp and goldfish belong to, fulfil the criteria for animal pain [2].

Why do some scientists say fish can’t feel pain?

Some scientists argue that all of this could be nociception, the unconscious detection of damage, with nothing felt. One detailed version of the case, made by Rose and six co-authors in 2014, holds that the experiments failed to tell the two apart and were often misinterpreted or not replicable, that fish feed and move normally soon after surgery, that C-fibre nociceptors, the commonest type in mammals and responsible for excruciating pain in humans, are rare in teleosts, and that fish lack the cortical regions pain depends on in humans [4]. Brian Key (2016) argued that fish lack the brain structure and wiring needed to feel pain [5], and in 2019 Browman and eleven co-authors, Rose and Key among them, concluded that fish are unlikely to experience pain as the International Association for the Study of Pain defines it [6]. Sneddon’s work answers that in trout the A-delta fibres, which are the commonest type there [1], work as polymodal nociceptors, doing the job C fibres do in mammals [3], and that birds evolved brain regions organised differently from the mammalian cortex that play analogous roles, so a brain built unlike ours need not rule pain out [2]. Proof of what another being feels is out of reach for any animal, and nobody asks for it before accepting that a dog or a pig is in pain. The New York Declaration on Animal Consciousness (2024), which had more than 600 signatories by October 2026, holds that the evidence shows at least a realistic possibility of conscious experience in all vertebrates, fish included [7]. In the UK, the Animal Welfare (Sentience) Act 2022 counts every vertebrate, fish among them, in its provisions on the welfare of animals as sentient beings [8].

Do fish feel pain when they suffocate?

They may well: in rainbow trout taken out of water the brain keeps functioning for minutes, and far longer if the fish are chilled [9]. Kestin and colleagues (1991) found that the trout kept their visual evoked responses, the brain’s electrical reaction to what the eyes see, for 2.6 minutes on average at a body temperature of 20°C and 9.6 minutes at 2°C, and took 11.5 and 197.6 minutes respectively to stop moving altogether [9]. The authors concluded that fish killed by lack of oxygen could be exposed to periods of distress or suffering, and that cooling them in ice prolongs it [9]. Mood and Brooke (2024), of the fish welfare site fishcount.org.uk, estimate that 1.1 to 2.2 trillion wild fish were caught each year on average between 2000 and 2019, and describe their welfare during and after capture as generally very poor [10]; how wild and farmed fish are killed has its own page.