In the scientific world the line between simply reacting to negative stimuli and “feeling pain” is marked by the capacity to process and express emotions.
“Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”
- The International Association for the Study of Pain
Thus one of the main arguments scientists use against fish feeling pain is that their brains lack certain structural elements, most importantly the neocortex, which, in other animals such as humans, processes negative stimuli into emotions. The second common argument is that their amygdoid complex (similar to our amygdala which helps us process emotions) is wired to produce aggression and not fear. The reason this is important to our sense of “feeling pain” is because our pain response also comes with a negative emotional reaction which in turn excites the amygdala and helps form a memory of the damage done to our bodies by a particular stimulus.
As you can see, in any species of animal, the concept of feeling pain is a complex one. What scientists are really trying to prove is not only that fish sense the negative stimuli damaging their bodies, but also despite the differences between their brains and ours, that they also have the capacity to associate emotions with the damage done. And some scientists claim to have proven just this.
Next: What the studies say