The question of whether fishes feel pain can elicit very emotional responses from some people.
Looking at a hooked fish or a fish asphyxiating in a drying stream, one cannot help but attribute human feelings of pain and suffering to the fish.
A team of researchers led by Dr Lynne Sneddon in Scotland have concluded that fishes do feel pain.
This conclusion was based on experiments during which trout were injected in the lips with bee venom and acid. The researchers then confirmed that a nervous response was transmitted and the behaviour of the fish modified.
Dr J. Rose of the University of Wyoming on the other hand states that the perception of pain and fear in fishes is very different from that of humans.
He argues that it is important to first distinguish between pain and the reception of noxious (harmful) stimuli (nociception). Without doubt both fishes and humans respond to noxious stimuli. A fish that has been hooked is obviously responding to a stimulus. Likewise, if you burn yourself, you will very quickly respond to the stimulus, however this response occurs before you feel any pain. Nociception is controlled by the spinal cord and brainstem.
Rose states that the difference in the perception of pain and fear in fishes and humans results from differences in brain structure. The human brain has a massively developed cerebral cortex (the grey folded outer layer). Pain and fear in humans results from the stimulation of several regions of the cerebral cortex. The tiny cerebral cortex of fish brains lack these regions.
The lack of the comparable regions of the brain is one of the arguments that Rose uses to conclude that fishes do not experience pain and fear.
Most of the "everyday behaviour" of a fish is controlled by the brainstem and spinal cord. Experiments in which the cerebral hemispheres of fishes were removed have shown that even without these parts of the brain, fishes can maintain normal function and behaviour. Interestingly a human with complete destruction of the cerebral cortex will still respond to noxious stimuli, but feels no pain.
Despite the apparent lack of pain as we know it in fishes, they most definitely suffer from stress. Rose states that they "display robust nonconscious, neuroendocrine and physiological stress response to noxious stimuli".
In short, if you need to touch a fish, you should remember that the fish may not experience pain the way you do, but it does suffer from stress. Professional ichthyologists follow stringent guidelines to reduce stress when handling fishes.
Here's the article, I accidentally found it online and thought I might want to share it with you guys.