Shell-shocked crabs feel pain and scuttle out of their way to avoid it, new research has suggested.
The study involved exposing crabs to mild electric shocks and scientists say it raises ethical implications for the food industry, and whether we should be kinder to crustaceans.
The team, from Queen's University in Belfast, devised an experiment designed to distinguish between pain and unconscious reflex action.
Lead researcher Professor Bob 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 common shore crabs were allowed to hide under one of two dark shelters in a tank.
Those that picked the wrong shelter received an electric shock. When they were returned to the tank, most chose the same shelter again and were shocked a second time. But after this, the vast majority decided enough was enough. Placed in the tank for a third time, they switched to the alternative dark shelter.
Crabs that chose the "safe" shelter first off continued to use it, according to the research, which was reported in the Journal of Experimental Biology.
"Having experienced two rounds of shocks, the crabs learned to avoid the shelter where they received the shock," said Prof Elwood. "They were willing to give up their hideaway in order to avoid the source of their probable pain."
He said the findings showed that crabs were aware of pain and did not simply react with a type of reflex action called 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," said Prof Elwood. "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."