Crayfish may be smarter than we thought, as a study finds they can experience "anxiety"

Crustaceans really are spineless, according to a recent study in the journal Science.

Sign Up

Get the New Statesman's Morning Call email.

It’s not just humans who love to worry. New research at the University of Bordeaux has demonstrated that crayfish subject to high stress will develop anxiety-like symptoms – but human medicines can cure them of it.

The study is one of many in recent years to highlight the potential for emotional intelligence in non-humans. The researchers, from the Aquitaine Institute for Cognitive and Integrative Neuroscience (INCIA), managed to induce a state of anxiety in the fish, which they subsequently cured by administering drugs.

After being exposed to a stressful electric field, a group of crayfish were placed in an aquatic maze. Two arms of the maze were left dark, to replicate the crustaceans’ original environment; the others were illuminated with bright lights.

The team found that the control group (crayfish who hadn’t been shocked) explored the entire maze, while exhibiting a slight preference for the darker areas. Conversely, the group which had been subject to the electric field rarely ventured into the light areas at all, as if they were too scared or nervous to confront the unknown.

Team leader Daniel Cattaert, associate research director of INCIA, believes this highlights the similarities between “primitive” crayfish and ourselves: “[The results] emphasise the ability of an invertebrate to exhibit a state that is similar to a mammalian emotion."

Such wariness in non-sentient beings has previously put down as simple ‘classical conditioning’ – a learning process that occurs when two stimuli are paired, as with Pavlov’s dogs. Crayfish may develop a fear of the unfamiliar, but that doesn’t necessarily mean they suffer from anxiety in the human sense of the word, does it?

Well, no. But in this experiment the two stimuli (the electric shock and the bright light) were not paired. If the crustaceans’ actions were based solely on learned experiences, they shouldn't have had any reason to fear the light. However, the it seems the stress of the shocks had put them on a sort-of ‘red-alert’ mode. The stressed crayfish were too nervous to explore areas that their "naive" counterparts were happy to. This was evident by the accompanied release of high levels of serotonin, a chemical used by the brain to combat feelings of stress and anxiety.

To investigate this apparent anxienty further, the team administered the stressed fish with a ‘BZD’ – a type of psychoactive drug commonly used as anxiety medication. The authors discovered that the cautious behaviour amongst the crayfish “was abolished" almost immediately, meaning that the crayfish were successfully treated for anxiety with human drugs.

This doesn’t indicate high-level emotion processing within crustaceans, but it does suggest the anxiety mechanism in humans is also present in crayfish – a species classified by the European Food Standards Authority as non-sentient. Speaking to the BBC, zoologist Bob Elwood said: “This work shows the behaviour is consistent with a state of anxiety... but you cannot ask a crayfish how it feels.”

They might not be signing up for group therapy anytime soon, but crayfish are certainly susceptible to bouts of apprehension.