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Thursday, May 15, 2003
Fish have feeling too
By ROWAN HOOPER
"It's OK to eat fish 'cos they don't have any feelings." So sang Kurt Cobain on "Something in the Way," from 1991's "Nevermind" album.
We all know that Kurt felt pain -- he wouldn't have made such good records if he didn't. But do fish feel pain? It's a concept that many vegetarians, anglers, researchers working on animal behavior, and animal-rights activists ponder. (For those people in Japan who, like many in France, are not aware of the concept of "animal rights," it is the proposal that animals be accorded similar treatment and protection from exploitation that we accord humans.)
Birds and mammals, research has shown, can feel pain. But coldblooded fish? Until recently, there was no conclusive answer. Now scientists from the Roslin Institute and the University of Edinburgh in Scotland have provided one, showing for the first time that pain perception exists in fish.
Their study, published in the Proceedings of The Royal Society, was undertaken on rainbow trout and demonstrates two points crucial to arguing that an animal feels pain. First, the researchers found that there are nociceptors -- nervous-system receptors -- in the head of the fish and that these respond to tissue-damaging stimuli. Second, they found that the application of noxious substances produced profound behavioral and physiological changes in the fish over a prolonged period of time. These changes are comparable to those observed in higher mammals.
This indicates, the researchers believe, that fish can perceive pain.
But not all of them. Fish are divided between into two major groups, the elasmobranchs (which include the sharks, rays and skates) and the teleosts (bony fish).
"Previous work on fish has looked at the elasmobranch family, such as stingrays, and primitive vertebrates like the lamprey," said Lynne Sneddon, who led the research at the Roslin Institute and is now working at the University of Liverpool in England. "Those studies did not conclusively show the presence of nociceptors. We believe that our study is the first work with fish of the teleost family and the results may represent an evolutionary divergence between the teleost and elasmobranch lineages."
The presence of nociceptors in the rainbow trout was determined using electrophysiological recordings. Neural activity was recorded in anesthetized fish while mechanical, thermal and chemical stimuli were applied to the head. "We found 58 receptors located on the face and head of the rainbow trout that responded to at least one of the stimuli," said Sneddon. "Twenty-two of these could be classified as nociceptors in that they responded to mechanical pressure and were stimulated when heated above 40 degrees. Of these, 18 receptors also responded to chemical stimulation and can be defined as polymodal nociceptors."
The polymodal nociceptors found in the trout are the first to be found in fish and have similar properties to those found in amphibians, birds and mammals, including humans. But the receptors were more sensitive than those found, for example, in human skin. The fish nociceptors were more like those on a human eyeball.
"The nociceptors were extremely sensitive and so I suppose it is the same as touching the eyeball," said Sneddon in an e-mail interview. "I think the fluid nature of their environment would have a lot to do with this sensitivity. Fish have a mucus layer as their first line of defense against disease. If that is disrupted or rubbed off this leaves them open to various infections. This is especially true for freshwater fish."
Sneddon and colleagues established that trout have nociceptors, but still needed to demonstrate that their stimulation causes adverse behavior and physiological change. To do this the researchers injected bee venom or acetic acid into the lips of some trout, while other fish were injected with saline solution or merely handled to form control groups. All fish had previously been conditioned to feed at a feeding ring in their tank where they were collected for handling and/or injection.
"Anomalous behaviors were exhibited by trout subjected to bee venom and acetic acid," said Sneddon. "Fish demonstrated a 'rocking' motion, strikingly similar to the kind of motion seen in stressed higher vertebrates like mammals, and the trout injected with acetic 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."
The acid- and bee venom-injected fish also took almost three times longer to resume feeding activity compared to the saline and handling control groups. The time taken to resume feeding did not decrease in experiments with fish conditioned to feed on "softer" food.
The results satisfied the scientists. "This fulfills the criteria for animal pain," said Sneddon.
So should these findings change the way we think about fish welfare? Does this mean fishing is a blood sport, like other forms of hunting?
"I think the difference between fishing and fox hunting is that we eat the fish therefore there is a benefit to humans," said Sneddon. "There is no other way of catching fish than by hook or by netting. I think we should be seeking to refine our equipment and practices so that we cause minimum suffering to the fish. I think animal-rights [activists] will adopt the data, but they will condemn me for doing the experiments. I hope the government takes the results on board and improves the regulations governing the treatment of fish."
Going back to Kurt Cobain, is it still OK to eat fish, now we know they have feelings?
"I need to make the point that animal pain is not the same as human pain; you cannot prove an animal has an emotion," said Sneddon. "I think no animal will feel anything like what humans experience, but if they are suffering or in discomfort this is no less important biologically or ethically."
Rowan Hooper welcomes comments at firstname.lastname@example.org