New research conducted by Swedish researchers finds that anxiolytic drugs in surface waters alter animal behaviours that are known to have ecological and evolutionary consequences

Researchers from Umeå University in Sweden examined how perch behaved when exposed to oxazepam, a drug commonly used to treat anxiety disorders in humans.

The scientists exposed the fish to concentrations of the drug similar to those found in the waters near densely populated areas in Sweden.

The researchers conducted a “boldness test” on the perch, opening a door that would allow them to swim from a small box into a much larger water tank. The fish with no drugs in their system remained timid and “didn’t come out at all,” he said, while those on oxazepam did.

Such behaviours, coupled with the tendency to scarf down food faster than normal, could alter the composition of the species and lead to ecological changes in the real world.

Although scientists focused on just oxazepam in their research, they noted that residue from a “veritable cocktail of drugs” can be found in waterways worldwide.

Normally, perch are shy and hunt in schools. This is a known strategy for survival and growth. But those who swam in oxazepam became considerably bolder

Tomas Brodin. ecologist, Umeå University, Sweden