Study finds crayfish treated with antidepressants become more outgoing, adventurous

A study by freshwater crustacean boffins in Florida has revealed that feeding antidepressants to crayfish can make them more outgoing and adventurous — which is more or less a definition of how antidepressants are supposed to work. On humans, at least.

The experiment set out to investigate how exposure to antidepressants might affect crayfish behaviour in the wild, since human pharmaceutical pollutants are an increasing factor in freshwater environments.

To do this, they created “20 oval-shaped recirculating artificial streams,” each of which they filled with 60 litres of chemical-free groundwater. In each artificial stream, they built a shelter at one end for the crayfish to start in, which led to two separate paths: one flavoured with fish gelatin to signal a source of food; the other populated by another crayfish to potentially provoke an aggressive response.

Once they had been exposed to small amounts of a common antidepressant called citalopram, the excitingly named spiny-cheek crayfish used in the experiments (aka Faxonius limosus) emerged from shelters in half the time they did in control groups and spent twice as much time out in the open foraging for food.

Spiny-cheeked crayfish are native to water courses across the east of North America, but are also increasingly common in Europe and elsewhere, where they are considered an invasive species and a pest.

“I don’t think any of us really expected such drastic changes in the crayfish behaviour,” said AJ Reisinger, lead author of the study and Assistant Professor in the Soil and Water Sciences Department at the University of Florida.

As Lauren Mathews, an ecologist of freshwater systems at Worcester Polytechnic Institute, told Voice of America News: “Ecosystems are really complex, and extrapolating out what’s going to happen from the removal or increase of one species is really difficult. But there probably would be an impact.”

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The fact the crayfish were spending more time out in the open means they could suffer more from predation, for example, while the fact they were spending more time foraging for food could have an impact on the stability of the food chain.

The Florida study did not confirm either case, but human pollutants in freshwater environments can have unpredictable outcomes. A 2019 study of freshwater shrimp across 15 locations in rural Suffolk, UK, found that every single one contained traces of cocaine, with some also baked on ketamine.

Studies in both Britain and the US have also found that fish populations can be affected by the presence of synthetic female hormones in polluted water, leading to male fish changing their sexual characteristics.

Another study suggested that wastewater flowing from two drug-manufacturing facilities contained pharmaceuticals, including opioids, at ten to 1000 times the concentrations found in normal outflows, potentially giving freshwater creatures yet another opportunity to get high — albeit with presumably the opposite outcome to the outgoing crayfish in the Florida study.

While the presence of such chemicals in natural ecosystems is troubling, the study might at least be of use to owners of morose crayfish interested in persuading their pets to come out of their shells. ®