\u2022 Fish are often dismissed as alien and simple, which makes it easy to overlook the true complexity of their lives and the massive numbers in which we use them.<\/p>\n
\u2022 Most scientists believe fish feel pain. But the question remains surprisingly contested, because subjective experiences are very hard to prove.<\/p>\n
\u2022 The keys to understanding the evidence that fish feel pain, and why some scientists remain skeptical.<\/p>\n
\u2022 How clashing paradigms have shaped the way we understand animal consciousness, from the Scientific Revolution to the present.<\/p>\n
\u2022 Why \u201ccan fish feel pain?\u201d may be, in the end, the wrong question.<\/p>\n
This story is part of a series supported by Animal Charity Evaluators, which received a grant from EarthShare.<\/p>\n
And so it remains today: Humans use fishes in far greater numbers<\/a> than we do land animals \u2014 for food, for amusement as pets, and more \u2014 but our species shows strikingly little interest in what these experiences might be like for them. We even use fish as bywords for stupidity and poor brain function, like the proverbial goldfish mind<\/a> that resets every three seconds \u2014 a myth fabricated out of thin air<\/a>.<\/p>\n But I should speak for myself. Although I\u2019m professionally obsessed<\/a> with the ethics of our relationships with nonhuman animals, I\u2019m somewhat embarrassed to admit I\u2019ve given little thought to the massive class of animals that we call fish. I\u2019ve hardly written a word about the hundreds of billions killed \u2014 quite<\/a> brutally<\/a> \u2014 by the commercial fishing and fish farming industries every year, nor much considered why it is that aquatic animals are treated as an afterthought to those who live on land.<\/p>\n Fish are hard to empathize with. They lack facial expressions we can readily understand, their bodies are scaly and cold to the touch, and although they make plenty of sounds to communicate with one another, we generally can\u2019t hear them. Their entire world \u2014 built on senses and signals that we land-bound creatures cannot access \u2014 is as alien to us as ours no doubt is to them.<\/p>\n Golden butterflyfish glide over a coral reef. Colin Baker\/Getty Images<\/p>\n \u201cWe know very, very little about their day-to-day lives,\u201d Becca Franks, an assistant professor of environmental studies at New York University, told me. \u201cRather than seeing that big blank murky fogginess as a mystery that is waiting to be unveiled\u2026there\u2019s a cultural expectation that their lives are simple and not interesting.\u201d<\/p>\n In recent decades, however, our aperture on marine life has widened tremendously. Scientific advances have increasingly shown that we\u2019ve misjudged fish. They have complex social relationships<\/a> and cognitive abilities<\/a>, maintain long-term memories<\/a>, and use tools. Octopuses \u2014 invertebrates with even more genetic distance from humans than fish \u2014 have become international celebrities for their intelligence<\/a>. The more we attempt to look into the minds of animals farther and farther from us on the evolutionary tree, the more we discover how much we\u2019ve been underestimating them.<\/p>\n Yet even as it has shed new light onto the piscine creatures that populate most of our planet, the science of fish minds has been mired in debate over a startlingly, deceptively simple question: Can fish feel pain?<\/p>\n It might sound weird that a capacity as basic as pain is still contested in animals who can distinguish between individual human faces<\/a> and migrate thousands of miles<\/a>. But the question remains unsettled because pain is a subjective feeling that science cannot prove definitively. And so, even as experimental evidence that fish experience pain<\/a> has accumulated over the last quarter-century, some prominent skeptics continue to doubt it.<\/p>\n The great fish pain debate<\/a> shows us how scientific knowledge is shaped not just by linear progress, but also by historical contingency, cultural biases, philosophical roadblocks, and internal ethical paradoxes. And it reflects back a story about us humans \u2014 our endeavor to find sentience in our fellow creatures, and our countervailing impulse to deny morally important qualities in them.<\/p>\n Perhaps nowhere are these competing tendencies more evident than in our attempts to understand fish, alien as they are to our warm-blooded, mammalian selves.<\/p>\n What we talk about when we talk about fish pain<\/p>\n Most accounts of what we know about pain in fish go something like this: Until very recently, it was widely believed that fish don\u2019t feel pain, or much of anything. There\u2019d been little empirical work on the question. Then, in the early 2000s, a group of University of Edinburgh researchers \u2014 Lynne Sneddon<\/a>, the late Victoria Braithwaite, and Michael Gentle \u2014 transformed how we see fish.<\/p>\n They discovered<\/a> that fish have nociceptors, or neurons that send signals to the central nervous system when an animal is injured. Nociceptors are considered necessary for experiencing pain, just as photoreceptors are for vision, but on their own, they aren\u2019t sufficient<\/a> \u2014 the animal needs to be able to perceive pain in the brain. So Sneddon and the team, along with other researchers after them, ran behavioral experiments designed to figure out whether fish really feel pain \u2014 whether their nociceptors aren\u2019t just reacting reflexively to noxious stimuli, the way a human involuntarily pulls away after touching a hot stove microseconds before feeling any pain.<\/p>\n Over and over again, the findings have pointed to yes. Goldfish and trout<\/a> prodded with needles showed not just reflexive responses, but also activity in parts of their brains associated with higher processing. When rainbow trout were injected with painful substances<\/a>, like acetic acid or bee venom, their respiration rates spiked, their appetites dropped, they rocked back and forth, and they rubbed the affected areas against the gravel and walls of their tanks, like pressing your tongue against a sore tooth. In other<\/a> experiments<\/a>, trout injected with acid altered their social behavior and diminished their fear responses to predator cues and novel objects, findings that, the scientists believed, suggested the fish were directing attention to the pain and away from normal behaviors. Goldfish avoided swimming<\/a> to parts of their tanks where they received electric shocks, sometimes even (depending on their hunger levels) forgoing food.<\/p>\n In the decades following World War II, scientists had increasingly begun studying animal well-being in the novel field of animal welfare science, as food production industrialized and the public grew concerned about the treatment of animals in the meat industry. But before Sneddon started her work on fish pain in the late \u201990s, fish had mostly been ignored by the field; the focus had been on land animals like chickens, pigs, and cows. \u201cAt that time, even vegetarians would say, \u2018Oh, I eat fish because they don\u2019t experience pain,\u2019\u201d Sneddon, now a professor at the University of Gothenburg in Sweden, told me. \u201cYou even hear it in the Nirvana song,\u201d she said, where Kurt Cobain drones<\/a>, \u201cIt\u2019s okay to eat fish, \u2019cause they don\u2019t have any feelings.\u201d<\/p>\n Darwin\u2019s ideas belong to an intellectual lineage that takes animal feeling for granted, as a constitutive part of what it means to be an animal.<\/p>\n Sneddon and other scientists like her do this work because they care deeply about aquatic animals and hope their findings can inform animal welfare policy, from which fish are so often excluded. Still, when I first learned about this research, something about it unsettled me. I found the idea that we needed to inflict painful, extremely invasive experiments onto fish \u2014 including not just pricking them and injecting them with acid, but also surgically opening their heads to place electrodes before killing them at the end \u2014 in order to prove they feel pain to be ethically self-defeating. Sneddon told me she\u2019s had \u201cguilt dreams\u201d where she was the one being injected with acid. Were there not less harmful ways to ask questions about the capabilities of fish?<\/p>\n And, surely, I thought, this was not the first time that scientists had ever thought about fish pain, nor the only way one could think about it. Although the history of Western thought is littered with disparaging ideas about aquatic life, we have a rich corpus to draw from for alternative ways of understanding the natural world and the experiences of fish. Charles Darwin, for example, wrote<\/a> in The Descent of Man that \u201cthe lower animals\u2026manifestly feel pleasure and pain, happiness and misery.\u201d He did not wonder about whether fish feel pain, Becca Franks, the NYU professor, told me, \u201cbecause he assumed that they did. He didn\u2019t find it to be surprising. He spoke easily and fluently about animal emotions across the animal kingdom.\u201d<\/p>\n Pearl mullet fish, a species that can jump over obstacles, in T\u00fcrkiye migrating to fresh waters by swimming upstream. Anadolu\/Getty Images<\/p>\n And even in modern science, Franks points out, land animals, unlike fish, have not been put through an intensive battery of experiments to test whether they can feel pain; researchers start from the assumption that they do. \u201cNobody\u2019s done these tests with chimpanzees,\u201d she said, nor has anyone felt obliged to set up a comparable research program in chickens to confirm whether their pain is real.<\/p>\n But with fish, \u201ctheir inferior status is evident even in arguments designed to grant them greater moral standing,\u201d Franks and a group of co-authors wrote in a chapter of the book Animal Dignity<\/a>. \u201cFishes, but not other vertebrates, are repeatedly asked, in increasingly elaborate experiential designs, to prove that they can feel pain.\u201d<\/p>\n Darwin\u2019s ideas belong to an intellectual lineage that takes animal feeling for granted, as a constitutive part of what it means to be an animal. \u201cHe said animals must feel pain, because it is an alarm system that alerts them to danger and stops you from injuring yourself,\u201d Sneddon said. But to understand why the fish pain debate remains a debate, we have to understand another, competing tendency that has shaped our view of animals since the Scientific Revolution: the idea, associated with the 17th-century French philosopher Ren\u00e9 Descartes and others, that animals are akin to machines without thought or feeling.<\/p>\n Science still doesn\u2019t understand consciousness<\/strong><\/p>\n \u201cDebates around fishes\u2019 ability to feel pain,\u201d scientists Georgia Mason and J. Michelle Lavery wrote<\/a> in 2022, \u201care essentially debates about consciousness.\u201d The sensation of pain, after all, requires an animal to be conscious \u2014 to have something that it\u2019s like<\/a> to be them. Sentience, a more specific form of consciousness, refers to an animal\u2019s ability to have positively or negatively valenced feelings, like pain and pleasure.<\/p>\n Science is still far from understanding<\/a> how and why consciousness arises, how widespread it is across our planet, and what the content of conscious experiences is \u2014 what it\u2019s like inside the mind of, say, a fish that evolved to navigate a world so different from our own.<\/p>\n \u201cOn the one hand is the brain, a tangible lump of tissue that can be handled, weighed, measured, sliced and publicly examined. On the other are our conscious experiences \u2014 vivid and all-consuming but private and known only to the one person experiencing them,\u201d biologist Marian Dawkins wrote<\/a> in 2017. \u201cHow the two are connected is still so unknown to us that to say that there is something mysterious and almost magical about it seems entirely appropriate.\u201d That means the scientific methods we have cannot prove that an animal \u2014 or even a human \u2014 is conscious.<\/p>\n Descartes, one of the fathers of modern science, helped codify the divide between the physical and the mental. He \u201csplit mind from matter, arguing that they are totally distinct: Only humans have mind,\u201d as Vox\u2019s Sigal Samuel has put it<\/a>. And he crystallized a premise now embedded deep in the foundation of modern science: that science is responsible only for the objective examination of things that can be independently verified, which almost by definition excludes subjective experiences.<\/p>\n Today, scientific approaches to animal minds land somewhere between the Cartesian and the Darwinian views. Most scientists, like most modern people generally, do not actually believe, as Descartes likely did, that animals are unfeeling automata. For the animals who are closest to us \u2014 like the baby pigs who cry out<\/a> when they\u2019re castrated on factory farms, or even the chickens bred to grow so big they struggle to walk \u2014 the capacity for pain is not seriously in doubt. But scientific consensus has not extended that courtesy to fish. And because consciousness is, at bottom, a philosophical question, whether or not fish possess it can be debated endlessly.<\/p>\n Mexican blind cave fish, a species with a supercharged ability to navigate the space around them by feeling subtle changes in the flow of water. Becca Franks calls it a \u201csixth sense.\u201d Getty Images\/iStockphoto<\/p>\n Some scientists argue that fish lack<\/a> parts<\/a> of the brain that they believe are necessary to feel pain, particularly the neocortex, a brain region that only mammals have. This is a minority view, dismissed by most experts who have researched pain perception in fish, who point out that there is no good evidence to believe that fish brains must process pain in the same way mammalian ones do. Birds also lack a neocortex, and even in humans, pain processing is distributed across different parts<\/a> of the brain. We don\u2019t understand either consciousness or the brain enough to claim that lacking a particular brain architecture forecloses the possibility of feeling pain. And it\u2019s worth noting here that this very critique of fish pain, according to<\/a> Franks and co-authors Jennifer Jacquet and Troy Vettese, traces back to fishing interests, who, reacting to the rise of animal welfare laws, helped create a research agenda disputing fishes\u2019 capacity for pain.<\/p>\n Because consciousness is, at bottom, a philosophical question, whether or not fish possess it can be debated endlessly.<\/p>\n Most experts in the field now do believe fish feel pain. But a more thoughtful, more serious challenge to the evidence comes from Georgia Mason, a behavioral biologist at the University of Guelph in Canada, who, in 2022, co-authored a review<\/a> of the fish pain literature that became a touchstone in the field. She and co-author J. Michelle Lavery called for tougher evidentiary standards in fish pain research, arguing that many of the types of pain tests that have been used in fish can also be passed by non-conscious subjects, like humans in unaware states and animals whose spines have been disconnected from their brains.<\/p>\n Decerebrate rats and chicks, for example, or animals who have had their forebrain function removed and are used as non-conscious comparators (controls) in consciousness debates, still show strikingly affective behavior, including licking or biting at injuries and vocalizing. If unconscious animals can do that, the authors argue, then a fish rubbing at their injuries is not very strong evidence of consciously felt pain.<\/p>\n In Mason\u2019s estimation, existing fish pain research consists of \u201cmore opinion than hard empirical work that was directly relevant to how fish feel,\u201d she told me. \u201cFaced with the question, \u2018How do you know this shows sentience?\u2019 I think a lot of researchers just start hand-waving at that point.\u201d She and her co-author propose ideas for experiments that they argue could more convincingly show that consciousness, rather than just reflexes, are involved in a pain response.<\/p>\n But Mason doesn\u2019t believe that fish don\u2019t feel pain \u2014 just that we haven\u2019t proven beyond a reasonable doubt that they do. She thinks we should take a precautionary approach, treating fish as though they\u2019re capable of pain and suffering until higher-quality evidence comes in. \u201cI really think that\u2019s the right thing to do,\u201d she said. That contrasts with the preferred approach of other prominent fish pain skeptics, who argue<\/a> that giving fish the benefit of the doubt could lead to animal welfare regulations that imperil the fishing industry and undermine food security.<\/p>\n Despite the inherent limitations of consciousness research, the Cartesian split that quarantined private experiences from science, Mason and plenty of other researchers like her believe that rigorous experimental designs can convincingly approximate consciousness. \u201cWe don\u2019t have a perfect marker of being sentient,\u201d she acknowledged. \u201cWe\u2019re never going to know for sure. And the trick is to try and close that inferential gap so it\u2019s as small as it can possibly be, so that really you have to do elaborate backflips to argue that an animal isn\u2019t sentient.\u201d<\/p>\n On a personal, human level, Mason said, she has felt the pull of recognition and connection to nonhuman animals, including fish. \u201cWatching free-living fish in the wild on a reef, I think you can immediately be convinced that of course they\u2019re conscious,\u201d she said. \u201cBut the question is: Is that feeling tapping into something real, or are we just tricking ourselves?\u201d<\/p>\n Here is another way of thinking about fish. Although there\u2019s a common misconception that fish are primitive, in evolutionary terms<\/a> \u2014 because humans, along with every living animal species, are descended from aquatic ancestors \u2014 the fishes alive today are nothing like the fish we\u2019re descended from. Fish have not stood still but have continued to evolve and speciate, just as the lineage that would become humans did. \u201cThere has been ample time for fishes to evolve complex and diverse behavioural patterns as well as the cognitive hardware that goes with it to match the diversity of ecological niches they occupy,\u201d wrote<\/a> Australia-based ecologist Culum Brown.<\/p>\n Part of the confusion stems from the very language we use. To even talk about \u201cfish\u201d as one undifferentiated mass impoverishes our understanding of them; it would be as sweeping as lumping all land animals into one category. There are just as many (and possibly more<\/a>) fish species as there are land vertebrates, and at least as much diversity among fishes as there is between toads, ravens, lions, and gorillas.<\/p>\n Fishes are, to state the obvious, very different from us. But there\u2019s no reason to assume that evolving to live in the watery realm that covers most of the Earth has necessarily made them less conscious or cognitively complex. Cleaner wrasse fish can recognize themselves<\/a> in a mirror, a finding that Mason calls \u201camazing and mind-blowing \u2014 it gives you goosebumps.\u201d As Vox contributor Garrison Lovely wrote<\/a>, \u201cguppies have friends<\/a>, salmon probably jump for fun<\/a>, monogamous convict cichlid fish exhibit more pessimistic<\/a> behavior after a breakup, and Japanese puffer fish make flirtatious art<\/a>.\u201d<\/p>\n Franks suggests there are more productive routes than trying to get to the bottom of the consciousness question. \u201cWe don\u2019t even understand how this works in humans,\u201d she said. Rather than ask \u201cis there a light on or not?\u201d inside fishes\u2019 minds, we might ask what different species of fishes want, what motivates them, and what interests them by observing their behavior and simulating the actual contexts in which they live.<\/p>\n![\"Six](\"https:\/\/www.europesays.com\/us\/wp-content\/uploads\/2025\/11\/GettyImages-200500177-001.jpg\"\/)
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