Do fish not feel pain?

Defining pain scientifically is a tricky business. You stub your toe and it hurts, but there is a lot more to pain than that. Pain begins in special cells that detect noxious stimuli called, thanks to the vagaries of Latin, nociceptors. These transmit signals to the central nervous system which percolate up through the brain. On the way they can set off reactions. Hurt your hand and it is reflexes in your spinal cord that react, well before the signals make it all the way to the cerebral cortex where, we gather, consciousness resides and you really feel the pain.

For fish though, things are a bit different. Sharks and rays don’t seem to have nociceptors, so as far as we can tell they can’t even begin to feel pain. Bony fishes do have nociceptors but — and this is where it gets tricky — we are not sure if they have the brains to feel pain like we do.

Imagine a person without a brain (go on, I’ll bet you have someone in mind already). Now, assuming they aren’t spineless as well as brainless, if you burn their hand they will still draw it away, because the sensory nerves stimulate the motor nerves directly in the spinal cord. But have they suffered from the pain? Without a brain there isn’t even really a “they” to suffer.

Fish don’t have a cortex, it’s a mammalian innovation. So they’re not conscious of pain, right? So conclude some scientists. Others aren’t so sure. Fish do behave in ways that suggest discomfort. What if the cortex is the wrong place to draw the line between animals that suffer and those that don’t? The first bunch of scientists think this is nonsense, that such behaviour is just reflexive, unconscious. Fish aren’t like you and me, they say, stop pretending they feel pain like us. The debate is a sure sign of uncertainty.

A hooked salmon does sense pain but whether it suffers is a much trickier question. Fish do feel pain — up to a point. Unfortunately we just aren’t sure what point that is.

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