'Shell-shocked' crabs can feel pain

Jan 16, 2013
This image shows the common shore crab, used in the research, with wires attached to deliver a mild electrical shock. Credit: Queen's University Belfast

The latest study by Professor Bob Elwood and Barry Magee from Queen's School of Biological Sciences looked at the reactions of common shore crabs to small electrical shocks, and their behaviour after experiencing those shocks. The research has been published in the Journal of Experimental Biology.

Professor Elwood's previous research showed that prawns and respond in a way consistent with pain. This latest study provides further evidence of this.

Professor Elwood said: "The experiment was carefully designed to distinguish between pain and a reflex phenomenon known as nociception. The function of pain is to aid future avoidance of the pain source, whereas nociception enables a reflex response that provides immediate protection but no awareness or changes to long-term behaviour.

"While nociception is generally accepted to exist in virtually all animals the same is not true of pain. In particular, whether or not crustaceans experience pain remains widely debated."

The tank used in the study housed two shelters for the crabs. Credit: Queen's University Belfast

This latest study showed that shore crabs are willing to trade something of value to them – in this case a dark shelter – to avoid future electric shock.

Explaining how the experiment worked, Professor Elwood said: "Crabs value dark hideaways beneath rocks where they can shelter from predators. Exploiting this preference, our study tested whether the crabs experienced pain by seeing if they could learn to give up a valued dark hiding place in order to avoid a mild electric shock.

"Ninety crabs were each introduced individually to a tank with two dark shelters. On selecting their shelter of choice, some of the crabs were exposed to an electric shock. After some rest time, each crab was returned to the tank. Most stuck with what they knew best, returning to the shelter they had chosen first time around, where those that had been shocked on first choice again experienced a shock. When introduced to the tank for the third time, however, the vast majority of shocked crabs now went to the alternative safe shelter. Those not shocked continued to use their preferred shelter.

"Having experienced two rounds of shocks, the crabs learned to avoid the shelter where they received the shock. They were willing to give up their hideaway in order to avoid the source of their probable pain."

Professor Elwood says that his research highlights the need to investigate how crustaceans used in food industries, such as , and lobsters, are treated. He said: "Billions of crustacean are caught or reared in aquaculture for the food industry. In contrast to mammals, crustaceans are given little or no protection as the presumption is that they cannot experience pain. Our research suggests otherwise. More consideration of the treatment of these animals is needed as a potentially very large problem is being ignored.

"On a philosophical point it is impossible to demonstrate absolutely that an animal experiences pain. However, various criteria have been suggested regarding what we would expect if pain were to be experienced. The research at Queen's has tested those criteria and the data is consistent with the idea of pain. Thus, we conclude that there is a strong probability of and the need to consider the welfare of these animals."

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User comments : 6

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TheGhostofOtto1923
2.3 / 5 (9) Jan 16, 2013
"On a philosophical point it is impossible to demonstrate absolutely that an animal experiences pain.
On a philosophical point it is impossible to prove anything. On a reality point however, OF COURSE animals feel pain. How else would they know to avoid things that are dangerous?? Good stimulus - stick around. Bad stimulus - run away.

We are animals. We experience pain. We have the same sorts of neurological systems as the other animals.
the need to consider the welfare of these animals
...the welfare of crabs. Of course.
eloheim
3 / 5 (2) Jan 17, 2013
I have to agree with TheGhostofOtto on this one. I was a little surprised to hear that it was debatable whether an animal as seemingly complex as a crab felt pain. I think this is a fascinating area of study, and the idea of quantifying this stuff interests me greatly.

In defense, the author did go to pains to explain the difference between the reflex, and pain. It does seem like there is a danger here of mixing technical and colloquial terms, especially in the mind of an average reader. Just the word pain obviously carries with it moral connotations. In this context, pain and suffering are usually associated with "stress," on an animal, and I'm assuming crabs will obviously show signs of being stressed when put in certain environments or subjected to certain stimuli.

I guess my main objection with the tenor or certain parts of the article is that science has taught us that these kinds of things tend to be continua, and this article puts it more in absolutes.
eloheim
3 / 5 (2) Jan 17, 2013
BTW, in case it wasn't obvious: I'm greatly supportive of this kind of study, and I'm glad the author wrote the summary for this site. I don't see how we're ever going to learn what it means to be humane without this kind of research.
ShotmanMaslo
3.3 / 5 (3) Jan 17, 2013


We are animals. We experience pain. We have the same sorts of neurological systems as the other animals.


Pain in this case meant something like suffering, not just the signal of pain. It is in no way obvious that lower animals suffer as the result of pain. They dont even have brain cortex. Thats why research like this is much needed.
TheGhostofOtto1923
1.9 / 5 (8) Jan 17, 2013
Pain in this case meant something like suffering, not just the signal of pain
Pain is pain. Discomfort is discomfort. Pain insists that you remove yourself from the stimulus. Not removing yourself causes further discomfort and stress. You are making it sound as if crabs would consider this arbitrary SM.
eloheim
1 / 5 (1) Jan 19, 2013
@ShotmanMaslo

I can't really make fault with your comments, if for no other reason than you are assessing the issue in an analytic, scientific way.

From my perspective though, the general trend in biology (both in the distant AND recent past) has been weighted towards revealing profound similarities between homo sapiens and the rest of the animal kingdom, as opposed to the opposite.

I'm speaking very generally here, but--see the relatively unexceptional human genome, and all the shared genes within the family tree, or the discovery of (rudimentary) "culture" in great apes-and now dolphins, the similarities of nervous systems throughout the mammalian order and beyond, etc.,--should at least give one pause before making TOO many assumptions. (And yes, these are crustaceans, but if you look to the example of the avian brain, it's MUCH less understood, and its UN-mammilian character make it difficult to assess/compare, yet e.g. parrots certainly appear to have "intelligence".

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