Further evidence crabs and other crustaceans feel pain
Scientists have found further evidence that crustaceans feel pain.
A study has revealed that the shore crab, a close relative of the species we use for food, responds to electric shocks and then goes on to avoid them.
Previous research has shown that prawns and hermit crabs also react to painful situations.
The scientists say the findings suggest the food and aquaculture industry should rethink how it treats these animals.
The work is published in the Journal of Experimental Biology.
Professor Bob Elwood, from Queen's University Belfast, told the BBC's Science in Action programme: "I don't know what goes on in a crab's mind.... but what I can say is the whole behaviour goes beyond a straightforward reflex response and it fits all the criteria of pain."
Pain is a subjective experience and studying it in animals - especially invertebrates such as crabs - is not easy.
But Prof Elwood designed an experiment to assess how crustaceans respond to potentially painful situations.
He looked at the European shore crab (Carcinus maenas) - a creature that usually takes shelter under dark rocks during the day to avoid being spotted and eaten by seagulls.
Ninety crabs were individually placed in a brightly lit arena, and had the option of scuttling to two dark shelters.
Once the creatures had taken refuge away from the light, half were given an electric shock in the first shelter they chose.
The shocked crabs were then placed back into the tank again, but to the researchers' surprise, most of them moved back to the original shelter where they had been stunned.
Those that made this decision were then shocked a second time. But now the painful experience had an impact on their future behaviour.
Prof Elwood said: "Those crabs shocked in the previous trial were much more likely to switch shelters than those who hadn't been shocked in the previous trial. Just two experiences produced a significant switch in behaviour.
"They leave what is a desired place - a dark shelter - to go out into this dangerous light environment - they are giving up something very valuable."
The crustaceans were placed back in the arena another eight times, and although there were no more shocks, they continued to avoid the shelter where they had been sparked.
The scientists concluded that this was more than a simple reflex reaction to pain, and that the animals were learning from their experience and this was driving their future choices.
Earlier work by the same team has also revealed that prawns and hermit crabs display behaviour that is consistent with our perception of pain.
They say they now believe that all decapod crustaceans - a group that also includes lobsters and crayfish - would show the same response.
Prof Elwood said that there were currently no regulations to protect the welfare of these animals.
He pointed to practices in some fisheries where claws are cut from live crabs before the animals are thrown back into the sea.
"You see these practices and you really do have to question whether they are reasonable... Even if you are reluctant to believe the data as being strongly suggestive [that the animals experience pain], is it worthwhile imposing this on billions of animals every year throughout the world?" he said.
Commenting on the research, Dr Lynne Sneddon, a senior lecturer at the University of Chester and the University of Liverpool, said the research was "thorough" and had been "carried out well".
Her research has focused on pain in fish, and said there were further avenues that the team could explore with crustaceans.
She said: "You could look to see whether there are any changes in gene expression, electrical activity or hormone release that is different from non-painful stimulation."
But a spokesman for the European Food Safety Authority (EFSA) said that while the organisation had concluded that fish could feel pain, in the EU, decapods were not classified as sentient species.
He said the subject of pain in crustaceans was "controversial" and a matter of data interpretation.
However, he added that in an earlier report about animals in laboratories, the EFSA had recommended improving the welfare for these animals.