Research from Queen’s University Belfast has raised new issues about the culinary arts. Long-thought by cooks and diners to be insensible to pain, a new study published in the journal Animal Behavior shows that crabs not only feel pain but remember it well-enough after the sensation has passed to affect their future decisions. According to Dr. Bob Elwood, who headed up the research, the study should bring about changes in how crustaceans like crabs are treated by the fishing and food industries.
To determine if crustaceans felt pain, Elwood attached wires to particular shells that would deliver small shocks to the hermit crabs inside the shell. Since hermit crabs do not have an attached shell like many crustaceans—using empty mollusc shells for protection—they are therefore able to abandon the shell at will.
Test-subject hermit crab. Photo by Bob Elwood.
The hermit crabs which were shocked were the only ones to abandon their shells, showing that the shock was painful enough for them to leave their protective home.
“There has been a long debate about whether crustaceans including crabs, prawns and lobsters feel pain,” Elwood said. “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. 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”.
Pushing the experiment further, Elwood tested at what level the shock would be small enough so that the crab would remain in the shell. At this point a new shell was offered to the crab. The hermit crabs that were shocked, even at a very low level, were more likely to move out of their shell and examine the new shell. They were also more likely to change their old shell—which had given them the shock—for the new one. Their reactions showed that not only are hermit crabs experiencing pain but they are remembering it well-enough to trade the first shell, which was a perfectly fine shell in every other way, for another, sometimes lesser, shell.
Elwood says that this trading of one shell for another is not dissimilar from how humans respond to pain. “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.”
Prior to this, Elwood has conducted research that showed prawns feel pain as well. However, Elwood points out that such research has not made its way to the fishing and food industries.
“More research is needed in this area where a potentially very large problem is being ignored…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.”
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