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How Fish React When Exposed to Human Anti-Anxiety Drugs

Swedish scientists test the change in fish behaviors when exposed to the drug oxazepam.

February 15, 2013

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Perca fluviatilis

European perch (Perca fluviatilis) Photo by D. Martin/Wikipedia
So what are anti-anxiety drugs and other pharmacologicals doing to fish? Scientists with Sweden's Umea University set out to find out how fish react to the human anti-anxiety drug oxazepam. The scientists focused on a schooling species of European wild perch (Perca fluviatilis) that lived downstream from a wastewater treatment plant in Sweden. The scientists had three test groups of perch, all hatched in a laboratory. They split the fish into three groups, one which lived in a tank with clean water, the second group which lived in a tank laced with levels of oxazepam similar to that found in the river, and the third group settled in oxazepam-laced water with up to 500 times that found in the river.

During the first week, the scientists ran a battery of tests to determine if the fish would congregate with each other, how fast that they would eat the zooplankton that is a staple of their diet in the wild, and how bold the fish would be to leave a dark box and venture out into the open.

After the second week, they again observed the fish, noting that the fish in the unmolested water performed the same way as they did a week prior. The fish with the low level oxazepam-laced water became more anti-social and spent less time with other fish, darted around more frequently and ate their fish food more quickly than the previous week, while the fish exposed to the highest levels of the drug became emboldened. While the no dose and low dose fish would not leave the confines of the dark box, the fish with the highest exposure to the anti-anxiety drug readily left the confines of the dark box. In fact, 23 of 24 of the fish left the box. It’s an extreme effect,” Tomas Brodin, assistant professor of ecology and an author of the paper told Time. “They get fearless. That’s bad, if you’re a little schooling fish,” he said.

An abstract of the paper is available on the Science Magazine website.

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