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This page was published on 20/04/2009
Published: 20/04/2009


Published: 20 April 2009  
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Agriculture & food  |  Pure sciences


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Crabs feel pain too, study shows

Looking forward to eating seafood tonight? You might want to think twice before you boil that crab. New research shows that crabs not only suffer pain but they also remember it. Professor Robert W. Elwood from Queen's University Belfast (QUB) said the work highlights the need to explore the treatment of crustaceans used in food industries. The study's findings were recently published online in the journal Animal Behaviour.

A hermit crab gets comfy in an empty shell © Shutterstock
A hermit crab gets comfy in an empty shell
© Shutterstock

Co-authors Professor Elwood and Mirjam Appel from the School of Biological Sciences at QUB studied the reactions of hermit crabs to small electric shocks. Hermit crabs inhabit structures such as empty mollusc shells because they are missing shells of their own. The objective of the experiment was to deliver a shock just under the threshold that drives the crabs out of their shells in order to determine what would happen when a new shell was offered to them.

The researchers attached wires to the shells and delivered small shocks to the abdomens of some of the crabs within these shells. The crabs that exited their shells were those that received the shock treatment, indicating that the experience was uncomfortable for them. According to the researchers, the result indicates that central neuronal processing occurs rather than the response being merely a reflex.

It should be noted that hermit crabs can by fussy about the species of shell they choose to occupy. The results of the experiment suggest that they are more likely to withdraw from the shells they favoured less.

The results also hint that the crabs that underwent shock treatment but chose to stay put appeared to retain a memory of the experience when they were presented with a new shell. The researchers found that they moved quickly towards the new shell and inspected it, compared with the crabs that did not receive the shock treatment.

'There has been a long debate about whether crustaceans including crabs, prawns and lobsters feel pain,' Professor Elwood pointed out. 'We know from previous research that they can detect harmful stimuli 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,' he added.

'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.'

Professor Elwood went on to say that people may hold on to a food-laden plate that is hot but will not hesitate to drop an empty plate. These responses demonstrate that humans consider differing motivational requirements when responding to pain. 'Trade-offs of this type have not been previously demonstrated in crustaceans,' the QUB researcher said. 'The results are consistent with the idea of pain being experienced by these animals.'

In previous research, Professor Elwood discovered that when acetic acid was applied to the antenna of prawns, they showed prolonged rubbing but this rubbing was reduced when they were treated with local anaesthetic.

The main difference, however, is that crustaceans used in the fishing and food industries have very little protection, mostly because people assume they feel no pain.

'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,' Professor Elwood underlined. 'With vertebrates we are asked to err on the side of caution, and I believe this is the approach to take with these crustaceans.'

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Journal of Animal Behaviour
Queen's University Belfast

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