By Phil Halper
Image credit: Clay Banks on Unsplash
For some of us, the answer to whether fish feel pain is an obvious yes. But alas, not everyone agrees. And in a world where at least a trillion fish are killed for human consumption each year, this question matters. Not only are fish killed for food, but angling is a pastime practised by hundreds of millions worldwide. Many justify these activities with the viewpoint that fish don’t feel pain, backed up by scientific studies. For example, the Sydney Morning Herald ran the article “Science debunks the myth of fish pain” with the tagline “The science is in – fish don’t feel pain. Anglers resume your pastime. Animal-rights activists retract the propaganda.” This is one of many similar articles that we can occasionally see online. But are they right?
Amazingly, the science of fish pain is relatively new. Before the 21st century, no one had researched to understand if fish have nociceptors, which are the relevant signalling pathways thought to be essential for an organism to feel pain. However, in 2003, Lynne Sneddon, Victoria Braithwaite, and Michael Gentle revealed that fish have these transmitters of pain.
But this was just a first step. Scientists often distinguish between nociception and affect, where affect refers to the emotional component of pain; that is, the sense of dislike one has when pain is present. Without affect, one can imagine organisms having an automatic response to avoid dangerous stimuli that don’t represent anything worthy of moral consideration. To probe for this, Sneddon and her colleagues elaborated an ingenious test to investigate deeper into a fish’s mind. They created a partitioned chamber with different environments. The first was barren and brightly lit, while the second had enrichment features such as plants and gravel with dim lighting. The Zebrafish studied favoured the second chamber. A harmful stimulus was applied, and the fish did not change their place of preference. However, when an analgesic was placed into the first (non-preferred chamber), the Zebrafish switched their chosen one, giving up its favoured chamber to consume the analgesics. In other words, they were willing to pay a cost to get some pain relief. A sure sign of conscious pain, or so one might think.
Image credit: Kindel Media on Pexels
This analgesic-seeking behaviour is not the only evidence for fish pain. Human beings who lack a particular gene called NTRK1, can’t feel pain and often injure themselves as a result. With today’s genetic technology, we know this gene is also present in fish. Other indicators seem to show an experience of pain. For example, fish usually show something called neophobia; in other words, they avoid novel objects. However, when they are exposed to painful stimuli, they don’t. This indicates pain changes their mental state in a similar way it does to us. They also rub the exposed areas just like we do. Fish also seem to experience anxiety, and in fact, Zebrafish are often used to screen new drugs for anxiety treatment in humans. Fish have also passed key tests for self-awareness.
Yet, the fish pain skeptics have a counterargument. They claim that the affective (emotional) side of pain is dependent upon the presence of certain cortical brain regions. The cortex enables higher thought and is especially developed in humans. It’s a relatively late evolutionary development, dating back tens of millions rather than hundreds of millions of years. One area of focus is a region that goes by the name Anterior Cingulate Cortex (ACC). This area is accosted with cognitive control and the regulation of emotions. Scans of people in emotional pain show increased activity in the ACC; if one severely damages the ACC, pain in humans can be eliminated. So, fish pain skeptics argue that the ACC is a necessary condition for pain effects, and as fish don’t have an ACC, they couldn’t experience pain at an emotional level. They believe fish ‘pain’ doesn’t matter, that it’s just an unconscious reflex.
However, any argument that depends on something being a necessary condition is vulnerable to what are known as ‘black swan’ events. For example, if someone states that most swans are white, finding a black swan won’t overturn their claim. However, if someone says all swans are white, then finding one black swan will. Similarly, if people claim that a rigid wing is needed to fly, then it makes no difference how many conventional airplanes there are, one hot air balloon will disprove this hypothesis. We can disprove the fish pain skeptics by finding one human that doesn’t have an ACC and yet still feels pain. While such patients are rare, the University of Iowa found a patient who had no ACC. This represented a unique opportunity to put the claims and disbelief of fish pain to test.
Image credit: Brian Forsyth at Pexels
Patient R experienced a debilitating Herpes simplex encephalitis that destroyed not only his ACC but other critical cortical areas as well, namely the insular and the prefrontal cortex. He had severe amnesia and much damage to his olfactory senses, and at first, this latter feature was what scientists were keen to study. However, his lack of a prefrontal cortex (PFC) eventually became the central area of research. Some theories of consciousness give a unique role to the PFC and suggested it was needed for self-awareness. These theories could be assessed by investigating R’s state of mind. Amazingly, his self-awareness, though tested extensively, seemed perfectly intact. The PFC was not needed for self-awareness after all.
If you met R, you probably wouldn’t have noticed anything unusual, unless you left the room and returned. He’d then quickly forget who you were, and you’d have to be re-introduced again. R’s apparent self-awareness made headlines worldwide as it implied complex human-type brains aren’t needed for self-consciousness. An animal without a PFC (non-mammals) can still be self-aware.
After this discovery, scientists started looking at Patient R’s pain perception. If the fish pain sceptics were right, R should have no pain affect; he might withdraw his arm from painful stimuli but wouldn’t report it as unpleasant. This is because R lacks the ACC, the insula, and the prefrontal cortex, key areas claimed as pain affect requirements.
Scientists don’t torture their patients to see if they can feel pain. A standard procedure is to ask them to place their hand in a bucket of water at zero degrees, which has a device to make it flow, stopping it from freezing. The patient is then asked to place their hand in the bucket for as long as possible but are allowed to withdraw it anytime. The ability to keep a hand in the bucket represents the patient’s tolerance to pain. Patient R’s tolerance for the bucket test was way below baseline, meaning he had an abnormally painful reaction to the stimulus, also known as hyperpathia. Scientists led by Justin Feinstein studied his withdrawal time, facial expression, heart rate, skin conductivity and interviewed him afterward. There was no doubt that he had pain affect and, more so than average. Just as the PFC was not needed for self-awareness, the ACC isn’t required for pain affect. Patient R is the fish pain sceptics’ ‘black swan’ event that we mentioned earlier.
Credit- 성두 홍 at Pexels.
The fact that the ACC lights up in pain studies doesn’t prove that it’s a necessary function for pain affect. Several other hypotheses can explain this. Firstly, it might be a coincidence as the ACC lights up in many different mental activities, so it’s no surprise that this happens during painful events also. Secondly, the ACC might light up because it’s trying to manage pain, as opposed to ‘initiating’ it.
The ACC’s importance in impulse control supports this theory. An animal without an ACC might then find the pain to be worse. Patient R’s hyperpathic pain response is further evidence to corroborate this hypothesis. A third option is that the ACC does ‘initiate’ pain but only contingently. So, in its absence, the brain will recruit something else for this essential function. Pain affect might then be subject to what’s called convergent evolution. Here, nature finds different pathways to undertake the same function. For example, we swim by using arms and legs. Fish don’t have human-like arms and legs, but they can still swim.
The fact that the ACC lights up in pain studies doesn’t mean it’s necessary to feel pain. What about those operations where the ACC was lesioned, and the pain disappeared? The results here hold up in the short term, but in the long term, we see a different picture; the pain eventually returns. This may imply the hypothesis mentioned before that the ACC is contingently involved in the pain effect. In its absence, something else will eventually take its place.
What is clear is that the higher cortical regions found in humans and other mammals aren’t needed for pain affect. The studies done by Sneddon and others cannot be countered by the lack of cortical regions. Fish and many other animals likely do feel pain. We might then rewrite the headline from the Sydney Morning Herald as follows: The science is in – fish do feel pain. Anglers abandon your pastime. Animal rights activists, resume your activities.
Watch the video
Some of the leading scientists in the field explain how they showed that fish feel pain. From the discovery of pain receptors in the early 21st century to finding a rare brain-damaged patient that enables us to dissolve the last objection of fish pain sceptics. Starring Lynne Sneddon, Mathew Parker, Phil Halper, Ken Williford, David Rudrauf, Perry Fuchs.
