Earlier this year researcher James Rose published an analysis of the brains of fish that concluded fish do not feel pain. In April, however, a team of researchers from the Roslin Institute and the University of Edinburgh published a study concluding that fish do feel pain. So who is right? Well, both are correct actually.
Not to be too Clintonian, but the debate over whether fish feel pain turns largely on the definition of “pain.”
The British researchers first anaesthetized fish and then subjected them to stimulation that would likely be perceived as painful in human beings. The researchers then watched how the fish responded to the stimulation.
Dr. Lynne Sneddon told the BBC,
We found 58 receptors located on the face and head of the trout that responded to at least one of the stimuli. Of these, 22 could be classified as nociceptors in that they responded to mechanical pressure and were stimulated when heated above 40 Celsius. Eighteen receptors also responded to chemical stimulation and can be defined as polymodal nociceptors.
The researchers also injected fish with bee venom or acetic acid and a control group with a saline solution. They found that the fish injected with the bee venom or acetic acid experienced behavioral changes. Again, the BBC quoted Dr. Sneddon as saying,
Fish demonstrated a ‘rocking’ motion, strikingly similar to the kind of motion seen in stressed higher vertebrates like mammals. The trout injected with the acid were also observed to rub their lips onto the gravel in their tank and on the tank walls. These do not appear to be reflex responses.
Animal rights organizations were quick to jump on this finding to support their cause. Dawn Carr of People for the Ethical Treatment of Animals told the BBC,
It’s shocking that people will still go fishing for fun. For every cruel thing people do, there is a compassionate alternative. There are so many ways to enjoy the outdoors — we hope people would go hiking, camping, boating, any sort of sport that doesn’t involved animal suffering would be preferable.
But what about Rose’s conclusion that the brains of fish are incapable of feeling pain? Well, there is a wide gulf between whether or not fish are capable of responding to painful stimuli and whether they feel pain. Dr. Bruno Broughton, an adviser to the United Kingdom’s Angling Alliance, outlined the difference in the BBC,
I doubt that it will come as much of a shock to anglers to learn that fish have an elaborate system of sensory cells around their mouths . . . However, it is an entirely different matter to draw conclusions about the ability of fish to feel pain, a psychological experience for which they literally do not have the brains.
Animals which do not have some sort of ability to change their behavior in response to external stimuli would be quickly selected out in nature. But it does not follow from this that all animals subjectively feel pain in the way that humans and other complex animals do.
As Rose summed it up in his paper,
Pain is predicated on awareness. The key issue is the distinction between nociception and pain. A person who is anaesthetized in an operating theatre will still respond physically to an external stimulus, but he or she will not feel pain. Anyone who has seen a chicken with its head cut off will know that, while its body can respond to stimuli, it cannot be feeling pain.
So a lot of it comes down to whether “fish feel pain” means that fish are capable of complex behavioral changes after being exposed to stimuli that would be painful to humans, or if it is meant that fish actually experience the same sort of psychological states that human beings and other animals do in the presence of painful stimuli.
Fish do feel pain, scientists say. Alex Kirby, The BBC, April 30, 2003.
Fish ‘capable of experiencing pain’. New Scientist, April 30, 2003.