Measurements show that crabs can process pain

Researchers from the University of Gothenburg are the first to prove that painful stimuli are sent to the brain of shore crabs, providing more evidence for pain in crustaceans. EEG-style measurements show clear neural reactions in the crustacean’s brain during mechanical or chemical stimulation.

The study is published in the journal Biology.

In the search for better welfare of animals that humans kill for food, researchers at the University of Gothenburg have chosen to focus on decapod crustaceans. This includes shellfish delicacies such as prawns, lobsters, crabs and crayfish that we both catch wild and farm. Currently, shellfish are not covered by animal welfare legislation in the EU, but this might be about to change. For a good reason, according to researchers.

“We need to find less painful ways to kill shellfish if we are to continue eating them. Because now we have scientific evidence that they both experience and react to pain,” says Lynne Sneddon, zoophysiologist at the University of Gothenburg.

Several research groups have previously conducted a number of observational studies on crustaceans where they have been subjected to mechanical impact, electric shocks or acids to soft tissues such as the antennae. These crustaceans have reacted by touching the exposed area or trying to avoid the danger in repeated experiments, leading researchers to assume that they feel pain.

Pain receptors in the soft tissues

The researchers at the University of Gothenburg are the first to carry out neurobiological studies by measuring the activity in the brain of a shore crab, through an EEG style measurement.

“We could see that the crab has some kind of pain receptors in its soft tissues, because we recorded an increase in brain activity when we applied a potentially painful chemical, a form of vinegar, to the crab’s soft tissues. The same happened when we applied external pressure to several of the crab’s body parts,” says Eleftherios Kasiouras, Ph.D. student at the University of Gothenburg and lead author of the study.

The activity of the central nervous system in the brain was measured in the crab when the soft tissues of claws, antennae and legs were subjected to some form of stress. The responses show that shore crabs must have some form of pain signaling to the brain from these body parts. The pain response was shorter and more powerful in the case of physical stress than in the case of chemical stress, which lasted longer.

Cut up alive

“It is a given that all animals need some kind of pain system to cope by avoiding danger. I don’t think we need to test all species of crustaceans, as they have a similar structure and therefore similar nervous systems. We can assume that shrimps, crayfish and lobsters can also send external signals about painful stimuli to their brain which will process this information,” says Kasiouras.

The researchers point out that we need to find more humane ways to handle and even kill crustaceans. At present, it is allowed to cut up a crustacean alive, unlike the mammals we eat.

“We need more research to find less painful ways to kill shellfish,” says Sneddon.