| | Stuart Derbyshire
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Give it a rest: fish do not feel pain
Yet another research project claims to show that fish are capable of feeling pain. It’s as wrongheaded as all the rest. |
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A team of researchers from Norway recently wrapped fish in foil in order to heat them up (1). Nothing new there you might think; that’s how I like to cook my fish, too. But these fish weren’t being cooked, they were being tested to see how they respond to intense heat while alive. Turns out that the fish try to escape and they try to escape even if they have received an injection of morphine. Two hours after being heated, the fish that didn’t receive morphine, however, behave more ‘cautiously’, by hovering in the same spot, than the fish that did receive morphine.
 One obvious interpretation of these findings is that heating fish up with and without morphine produces an observable change in behaviour two hours later. To put that slightly differently, doing different things to fish makes them do different things. This change in behaviour might be the consequence of some evolutionary advantage. Fish that keep still after being heated may have survived better and so genes for stillness after heat propagated.
The Norwegian researchers, however, draw a much more fanciful conclusion: that the fish feel pain and change their behaviour to avoid pain in the future. This conclusion has received considerable support, but it is certainly wrong (2). First, we can be certain that fish do not feel pain because they are made of fish. We may not precisely understand the relationship between mind and matter, but some relationship between brain and mind is certain, and fish have puny brains. Fish brains are about the size of your little finger nail and fish brains lack all the higher centres that neuroscientists associate with pain (3).
Second, we can be certain that fish do not feel pain because they lack subjective experience. Fish certainly have nerve fibres that process heat, but that’s not the same as feeling pain. The Norwegian researchers correctly quote the International Association for the Study of Pain’s definition of pain: ‘An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage… activity induced in the nociceptors and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state.’ (4) Sadly, however, the researchers never return to this definition to explain the psychological state of their fish.
What the definition is getting at is that pain is more than a physical-physical interaction. Pain is more than a physical-physical interaction because you don’t experience physicality. When you hear a sound, for example, you don’t hear a pure sound you hear a particular sound (the creak of a door, the squeal of brakes, the firing of a gun, and so forth). The physicality of the sound wave hitting your ears is a necessary part of the story, but what you hear taps into your understanding and knowledge about the world. And you acquired that knowledge by virtue of being and becoming a person. It is impossible to understand any experience without taking account of the whole complex of traits by which we are characterised.
Similarly when you feel pain you don’t feel the physicality of heat or the firing of neurons; you feel a burning sensation in a particular spot with a particular threat to it. There is nothing that persons experience that doesn’t drive down into the multi-layered psychological fabric of what persons are.
Fish aren’t like that. Heating living fish or heating dead fish might have different meanings for us (a wrongheaded experiment versus a tasty meal), but for the fish it is all the same.
Stuart Derbyshire is senior lecturer in psychology at the University of Birmingham in England.
(1) ‘Thermonociception in fish: Effects of two different doses of morphine on thermal threshold and post-test behaviour in goldfish (Carassius auratus)’, J Nordgreen, et al, Appl. Anim. Behav. Sci., 2009
(2) Do fish feel pain?, Guardian, 28 April 2009
(3) ‘The Neurobehavioral Nature of Fishes and the Question of Awareness and Pain’, JD Rose, Reviews in Fisheries Science, 10(1), 1–38, 2002
(4) ‘The definition of pain’, H Merskey, European Psychiatry, 6, 153-159, 1991
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