Do Fish Feel Pain?

Pete Wedderburn
9th June 2020 - 3 min read

Animal Welfare Issues

 There seems to be a traditional view in some parts of China that follows the opinion of Descartes, the French philosopher. He believed that animals were mere machines, devoid of sensation or feeling. If this view is followed, it’s perfectly acceptable to treat animals in the most inhumane way imaginable. It’s not that the people eating the live fish are being cruel: as far as they’re concerned, they might as well be eating a chocolate mousse. There’s no cruelty because fish are just objects, not sentient creatures.

Animals Feelings

We take a different view in the West: it’s universally accepted that animals have feelings, just like humans, and that it’s not acceptable to deliberately inflict pain on them. Our view is backed up by science, with research confirming the many similarities between animal and human nervous systems.

But even in our culture, there’s debate and controversy. People may accept that mammals feel pain, but what about fish? They’re so different to us, with their cold, scaly bodies, and their expressionless eyes.  When they react to a prod or a poke, could this be a basic survival reflex, or do they suffer the sensation of pain? Scientists have looked into this in different ways.

Rainbow Trout

rainbow trout fish in mans hands

In 2003, rainbow trout which had their lips injected with acid or bee venom were observed to rub the affected area on the gravel at the bottom of their tank, leading the researchers to conclude that they were in pain. But even then, some onlookers maintained that this could just be a reflex reaction.

Fish Pain Experiment

In recent times, a new experiment was devised. Researchers deliberately exposed goldfish to painful heat, by fitting them with a small electrically heated jacket that could be used to give a carefully controlled measure of pain. The jacket was set to go no hotter than 50’C so that the fish would not be physically harmed.

The fish were monitored carefully, turning off the heat as soon as they showed any signs of abnormal behaviour. The researchers wanted to be sure that they didn’t cause unnecessary pain to the fish during the experiment, so a fine line had to be negotiated: causing enough discomfort to prove that pain could be felt, but not so much that the animals suffered unduly.

Half of the fish were given a painkilling injection of morphine beforehand, while the other half were not. The small dose of pain was inflicted, and the fish were allowed to recover. Two hours later, the fish that had undergone the test without painkillers showed signs of fear and wariness, suggesting that they had suffered a bad experience and remembered it. The fish that had been given the morphine behaved normally.

goldfish swimming around water

Fish Reaction To Morphine

Morphine does not block out the nerve reflexes: it acts on the brain to remove consciousness of pain. The researchers maintained that the fact that fish with morphine behaved normally suggested there is some sort of central experience of the painful heat stimulus.

Of course, there’s always going to be room for debate here. Animals cannot communicate directly with humans, and until they tell us directly “Ouch, that hurt”,  skeptics can always try to maintain that the quality of pain that they feel may be different to the human experience. But there’s now enough evidence to tell us that we should treat all animals – including fish – with respect. We should take sensible steps to minimise the suffering involved when we handle animals, whether they’re dogs and cats, cattle and sheep, or even just fish.


There are still plenty of grey areas that we don’t understand. What about lobsters? They seem to scream when they’re plunged live into boiling water. Could they be feeling pain? The answer is: yes.

bright red lobster


And what about oysters, which many people in the West like to eat as living creatures? Could they be in pain as they travel down our gullet into our stomachs, where they’re slowly killed by our digestive juices? The jury’s still out on this one: scientists have not yet done experiments on oyster pain.

large group of oysters