Crabs have well-developed senses of sight, smell, and taste. New research now shows that crabs not only suffer pain too but also retain a memory of it.
The research, which is just published in the journal Animal Behaviour was carried out by Professor Bob Elwood and Mirjam Appel
Professor Elwood told BBC the research highlighted the need to investigate how crustaceans used in food industries are treated, saying that a "potentially very large problem" was being ignored.
Professor Elwood, who previously carried out a study showing that prawns endure pain, said: "There has been a long debate about whether crustaceans including crabs, prawns and lobsters feel pain.
"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.
Experimental setup
As part of the research, wires were attached to shells to deliver small shocks to the abdomen of some of the crabs. The study revealed the only crabs to get out of their shells were those which had received shocks, indicating that the experience was unpleasant for them.
Hermit crabs are known to prefer some species of shells to others and it was found that they were more likely to come out of the shells they least preferred.
The main aim of the experiment was to deliver a shock just under the threshold that causes crabs to move out of the shell, to see what happened when a new shell was then offered.
Those responsible for the study said crabs that had been shocked but remained in their shell appeared to remember the experience of the shock.
They said these crabs quickly moved towards the new shell, investigated it briefly and were more likely to change to the new shell compared to those that had not been shocked.
Trade-offs
"Trade-offs of this type have not been previously demonstrated in crustaceans. The results are consistent with the idea of pain being experienced by these animals."
Dr. Nedim Buyukmihci, professor of veterinary medicine at the University of California, Davis, explains: “Pain is a universal biological phenomenon in the animal world. It serves to protect an individual from internal or external adverse conditions. All animals studied to date have been demonstrated to have at least some means of responding to stimuli which would cause pain. Even invertebrates such as insects and earthworms have been shown to possess pain modulators which were commonly thought to exist only in vertebrates such as mammals. It is, therefore, completely rational and biologically sound to state that crabs would be able to feel pain. Moreover, their behavior is consistent with this principle.”
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