Scientists confirm crab's memory of pain

March 27, 2009
A hermit crab.

New research published by a Queen’s University Belfast academic has shown that crabs not only suffer pain but that they retain a memory of it.

The study, which looked at the reactions of hermit to small electric shocks, was carried out by Professor Bob Elwood and Mirjam Appel from the School of Biological Sciences at Queen’s and has been published in the journal Animal Behaviour.

Professor Elwood, who previously carried out a study showing that prawns endure pain, said his research highlighted the need to investigate how crustaceans used in food industries are treated. 

Hermit crabs have no of their own so inhabit other structures, usually empty mollusc shells.

Wires were attached to shells to deliver the small shocks to the abdomen of the some of the crabs within the shells.

The only crabs to get out of their shells were those which had received shocks, indicating that the experience is unpleasant for them. This shows that central neuronal processing occurs rather than the response merely being a reflex.

Hermit crabs are known to prefer some species of shells more strongly than others and it was found that that they were more likely to come out of the shells they least preferred.

The main aim of the experiment, however, was to deliver a shock just under the threshold that causes crabs to move out of the shell, to see what happened when a new shell was then offered.

Crabs that had been shocked but had remained in their shell appeared to remember the experience of the shock because they quickly moved towards the new shell, investigated it briefly and were more likely to change to the new shell compared to those that had not been shocked.

Professor Elwood said: “There has been a long debate about whether crustaceans including crabs, prawns and lobsters feel pain.

“We know from previous research that they can detect harmful and withdraw from the source of the stimuli but that could be a simple reflex without the inner ‘feeling’ of unpleasantness that we associate with pain.

“This research demonstrates that it is not a simple reflex but that crabs trade-off their need for a quality shell with the need to avoid the harmful stimulus.

“Such trade-offs are seen in vertebrates in which the response to pain is controlled with respect to other requirements.

“Humans, for example, may hold on a hot plate that contains food whereas they may drop an empty plate, showing that we take into account differing motivational requirements when responding to pain.

“Trade-offs of this type have not been previously demonstrated in crustaceans. The results are consistent with the idea of pain being experienced by these animals.”

Previous work at Queen’s University found that prawns show prolonged rubbing when an antenna was treated with weak acetic acid but this rubbing was reduced by local anaesthetic.

The findings are both studies are consistent with observations of pain in mammals.

But Professor Elwood says that in contrast to mammals, little protection is given to the millions of crustaceans that are used in the fishing and food industries each day.

He added: “More research is needed in this area where a potentially very large problem is being ignored.

“Legislation to protect crustaceans has been proposed but it is likely to cover only scientific research.

“Millions of crustacean are caught or reared in aquaculture for the food industry.

“There is no protection for these animals (with the possible exception of certain states in Australia) as the presumption is that they cannot experience pain.

“With vertebrates we are asked to err on the side of caution and I believe this is the approach to take with these crustaceans.”

More information: Animal Behaviour Journal, doi:10.1016/j.anbehav.2009.01.028

Provided by Queen’s University Belfast

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5 / 5 (3) Mar 27, 2009
As a person who dedicated his professional life to the amelioration of pain i do sympathize with the point of the article. I also sympathize with the newborn human male who is forced to endure circumcision totally without benefit of anesthesia. Should we not attend to this example of blatant disregard for the well-being of our own infants? If we can not do that, than little hope exists for finding methods of handling crustacae so as not to cause them to endure needless suffering.

Long ago I described a method of effectively circumcising baby boys that is without pain, bloodless, and safe. I did this to one patient at age 13 and followed his progress over many years. I can attest to the method's affectiveness although "one case does not an investigation make"!

I demonstrated this technique to several people and have yet to find that it is being done. I have concluded that the innertia of our medical care non-system, perhaps coupled with our society's preference for scalpel-related cures, has had a role in perpetuating the 'standard' circ methodology despite unnecessary suffering endured by our children, and, of course, the needless expense. It's even said, as was said about crustacae here, that " are not able to feel the pain." So, are we forced to believe that the screaming of the newborn under the knife must be due to some primal need to excercise his respiratory system??
5 / 5 (1) Mar 27, 2009
take a number and join the queue of "complainers". This world is patently unfair, you should know it, as the governance systems humans had in place are emphatically for the sole purpose of maintaining benefits and power and the status quo of the alpha-males of the whole shebang that is the mud ball called Earth. Take a deep breath, do yoga, or whatever to stop busting your brain' blood vessels. Nothing short of a mega meteorite to wipe out the whole mess will do any change. But, come to think of it, the dinosaurs was the apex of evolution in bygone age, and lasted for hundred of millions of years, without improving themselves before they were wiped out. Perhaps they too were religious and thought it was just the will of [their] God(s) and didn't do a thing to the contrary. Pissing up wind has been a chalenging pastime for untold bright sparks since amino acids replicate themeselves, and the results have been less than encouraging. I wish you luck in your Don Quixotean quest.

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