Crayfish can get just as anxious as humans - study

Feeling anxious? Photo / Thinkstock

Crayfish can feel anxious, according to a new study showing that "human" emotions are more widespread among animals than previously thought.

For the first time, scientists have found unequivocal signs that the state of anxiety normally associated with higher forms of life such as humans, mammals and other animals with a backbone, is also shared with a spineless species.

An experiment has shown that the freshwater crayfish can be induced into a state of deep anxiety that can only be alleviated by the same kind of tranquilisers used to treat people afflicted by a similar condition, scientists said.

The study revealed that the crayfish emotion is governed by the same chemical transmitters in its nervous system that are involved in controlling anxiety in humans, which is why anxious crayfish respond to benzodiazepine, a tranquiliser used to treat anxiety in people, scientists said

"Anxiety is different from fear, which is something that even the simplest animals show. Anxiety is a kind of fear of the fear, and animals who experience it will display adaptive behaviour to minimise the threat," said Daniel Cattaert, a neuroscientist at the University of Bordeaux in France.

"Acute anxiety can be beneficial. After an animal has faced a bad experience then if it adapts its behaviour to minimise the risk in the future, then this can be beneficial for the animal. People thought this only occurs in animals with complex nervous systems, but we have found it in crayfish," Dr Cattaert said.

Crayfish at the Tauranga Seafood Festival.

The study, published in the journal Science, involved subjecting crayfish to a series of mild electric shocks which, understandably, made them nervous and therefore prone to flicking their tails as an escape/response. They also changed their behaviour when compared with crayfish that had not been treated with shocks. Instead of exploring well-lit parts of the tank, anxious crayfish kept almost entirely to the darker corners.

"This adaptation in the stressed crayfish lasts for about an hour after being subjected to about 20 minutes of stress. A naive crayfish will readily explore the well-lit arms of the cross-shaped tank, but the stressed crayfish are clearly anxious about doing this," Dr Cattaert said. "There is clear decision making involved. They may start to enter the lit areas of the tank but then they stop and go back to the dark areas," he said.

When the stressed crayfish were treated with chlordiazepoxide, a potent benzodiazepine, they overcame their anxiety and readily explored the well-lit areas of the tank, showing no abnormal aversion to light, he added.

Injecting the neurotransmitter serotonin into unstressed crayfish, however, caused them to behave as if they had undergone the electric-shock treatment. Serotonin also plays a key role in governing the stress response in humans, suggesting there is a common origin of anxiety in crayfish and people, the researchers said. "Our results [suggest] the conservation of several underlying mechanisms during evolution," the study added.

- The Independent