The red swamp crayfish carries hundreds of tiny crustaceans on its back.
Credit: Juan Rueda Sevilla
Marc Bekoff, emeritus professor at the University of Colorado, Boulder, is one of the world's pioneering cognitive ethologists, a Guggenheim Fellow, and co-founder with Jane Goodall of Ethologists for the Ethical Treatment of Animals. Bekoff's latest book is Why Dogs Hump and Bees Get Depressed (New World Library, 2013). This Op-Ed is adapted from one that appeared in Bekoff's column Animal Emotions in Psychology Today. He contributed this article to Live Science's Expert Voices: Op-Ed & Insights.
Over the years, scientists have discovered that many animals feel pain including some "surprises." I put the word surprises in quotes because solid evolutionary theory — and good biology based on Charles Darwin's ideas about evolutionary continuity — strongly support the notion that a large number of animals should, in fact, feel pain.
For example, some animals were long excluded from the "pain club," but we know that they do indeed feel pain and are highly sentient beings, something I've addressed before in articles on pain in fish and similar findings for crabs.
Now, a new study has shown that crayfish, those delicious beings some people choose to eat, actually feel stress, and when given a drug used to treat that anxiety, respond as humans do. The results of the study are reported in the journal Science in an essay titled "Anxiety-like behavior in crayfish is controlled by serotonin."
The research team, led by Pascal Fossat of the Department of Life Science and Health at the Université de Bordeaux in France, concluded that this research "may alter our conceptions of the emotional status of invertebrates."
Studying crayfish anxiety
When Fossat and his colleagues mildly shocked crayfish in an aquarium maze containing pathways that were either well-lit or dark. The shocked and stressed crayfish strongly preferred the dark paths and rarely entered the lighted ones, whereas the non-stressed crayfish preferred the dark pathways but also entered the lighted ones.
What was incredibly interesting is that light avoidance by the stressed crayfish was associated with heightened levels of the brain neurotransmitter serotonin, a chemical also is associated with human moods. In addition, injecting crayfish with serotonin made them anxious and treating them with the drug chlordiazepoxide that's used to treat anxiety in humans reduced the anxiety in the stressed individuals — to the point the once stressed crayfish could again enter the lighted pathways. [How Animal and Human Emotions Are Different ]
When I read about this research, I was reminded of work that was done on honeybees that showed that they, too, show human-like responses to stress and depression. The bees showed altered levels of neurochemicals (dopamine, serotonin, and octopamine) that are associated with human depression. These fascinating studies show that we need to be careful making claims that invertebrates do not have emotional lives or feelings. In fact, these animals have marked similarities with vertebrates including humans.
Eliminating pain from the menu
Through research, humans are continually expanding the circle of sentience and consciousness and the Treaty of Lisbon — passed by member states of the European Union and placed into force on December 1, 2009 — recognizes that, "In formulating and implementing the Union's agriculture, fisheries, transport, internal market, research and technological development and space policies, the Union and the Member States shall, since animals are sentient beings, pay full regard to the welfare requirements of animals, while respecting the legislative or administrative provisions and customs of the Member States relating in particular to religious rites, cultural traditions and regional heritage." [After 2,500 Studies, It's Time to Declare Animal Sentience Proven (Op-Ed)]
Crabs, and many other invertebrates who supposedly don't feel pain, are served up as food in the countless billions, and many researchers agree that it's time to reconsider how these animals are treated in the food industry. I couldn't agree more.
Fish don't like being hooked and crayfish and lobsters really don't like being dropped, live, into boiling water. I expect more "surprises" will be revealed about sentience in other animal beings; they really do not live pain-free lives.
Bekoff's most recent Op-Ed was "Why Humanity Must 'Rewild' ." This article was primarily adapted from the post "The Emotional Lives of Crayfish: Stress and Anxiety" in Psychology Today. The views expressed are those of the author and do not necessarily reflect the views of the publisher. This version of the article was originally published on Live Science.