Do fish feel pain?

Last updated 25 September 2020

There has been much debate surrounding the ability of fish and other marine animals to feel pain. Land animals indicate pain in a way that is obvious to humans, often vocalising and trying desperately to escape the source of said pain. Fish and other marine animals react to pain in a way that is starkly different to humans and other land animals, consequently leading many to believe they simply don’t experience pain. 

There have been a number of experiments undergone to ascertain the ability of fish and other marine life to feel pain and to suffer.

*Note*: Farm Transparency Project does not condone the use of animals in experimentation, however, these experiments have been important in changing attitudes within the science community regarding fish, their sentience and ability to suffer. 

In one study a group of rainbow trout were given acetic acid injections into their lips, while a control group were injected with regular saline.

Of the fish who were given acid injections, their breathing became more rapid, they rocked back and forth on the floor of the tank, and rubbed their lips on the sides of their tank and pebbles, taking twice as long as the other control group to begin eating again following the injections.

In further experiments, fish were given morphine to dull the pain of the acid injections. Morphine acts to dull the experience of pain, however, does not cure the source of pain. So when the fishes’ behaviour returned back to normal, this suggested that the morphine was affecting their mental state and they were not responding to the acid in a mechanistic way. 

Preferences and avoiding pain

One experiment conducted by Lynne Sneddon, a University of Liverpool biologist and expert in marine biology, involved fish being given the option between two tanks in which to live. One tank was barren, the other was enriched with plant life, pebbles and a view of other fish. Fish consistently chose the tank that had enrichment over that which didn’t. However, when fish were injected with a painful acid and only the barren tank possessed pain-relieving lignocaine, fish consistently chose the barren tank. This experiment was repeated, however this time the pain relief was injected directly into the fish, and consequently they returned to choosing their preferred enriched environment.


Remembering pain

Not only do fish experience pain, but they also have the cognitive ability to remember it and actively try to avoid it. Fish can quickly learn to avoid negative stimuli and will continue to do so for long periods. Pike fish are known to experience ‘hook-shyness’ after being painfully caught on a fisherman’s hook and will actively avoid hooks for up to a year after the experience. Comparably, rainbow fish are able to learn the escape route from a net and remember it for up to a year after learning.


Fish sadness

Studies have found that as many as one in four farmed fish display behaviours and brain activity akin to that of severely stressed and depressed humans.