Swedish fish thrive on anti-anxiety drugs

Silver linings.

Not all man-made waste is detrimental to wildlife. Pike (perch) in waters contaminated with anti-anxiety drugs were found to be more social, had an increased survival rate on hatching and showed more activity 30 days after hatching. Generally the beneficial effects of man-made “contaminants” are neither expected nor looked for. “Most studies of risks from pharmaceutical pollution are conducted along the lines of standard tests for environmental toxins in ecosystems. …. and are structured in a way that hampers the detection of possible positive effects of medicinal contaminants”.

Perhaps anti-anxiety medication (like benzodiazepines or antidepressants or beta-blockers) could be used more widely – intentionally – for the mass treatment of unacceptably anxious or aggressive animals? I particularly like the comment that the fish were more social. I have a vision of man eating tigers being socialised on Prozac!

Nordic Science: Swedish scientists showed in 2013 that pike (or perch) that came in contact with water contaminated with the drug Oxazepam ― commonly used to treat anxiety ― exhibited changes in behaviour. They became more social and even more daring in their hunt for food.

Swedish researcher Tomas Brodin and his colleagues have returned with a new publication about the perch that lived in an experimental environment laced with antidepressants. They actually fared better than fish in water free of the drug. Fewer of the lightly drugged fish died over the course of the experiment.

J Klaminder et al, The conceptual imperfection of aquatic risk assessment tests: highlighting the need for tests designed to detect therapeutic effects of pharmaceutical contaminants, Environ. Res. Lett. 9 (2014) 084003, doi:10.1088/1748-9326/9/8/084003


Standardized ecotoxicological tests still constitute the fundamental tools when doing risk-assessment of aquatic contaminants. These protocols are managed towards minimal mortality in the controls, which is not representative for natural systems where mortality is often high. This methodological bias, generated from assays where mortality in the control group is systematically disregarded, makes it difficult to measure therapeutic effects of pharmaceutical contaminants leading to lower mortality. This is of concern considering that such effects on exposed organisms still may have substantial ecological consequences. In this paper, we illustrate this conceptual problem by presenting empirical data for how the therapeutic effect of Oxazepam—a common contaminant of surface waters—lower mortality rates among exposed Eurasian perch (Perca fluviatilis) from wild populations, at two different life stages. We found that fry hatched from roe that had been exposed to dilute concentrations (1.1 ± 0.3 μg l−1) of Oxazepam for 24 h 3–6 days prior to hatching showed lower mortality rates and increased activity 30 days after hatching. Similar effects, i.e. increased activity and lower mortality rates were also observed for 2-year old perch exposed to dilute Oxazepam concentrations (1.2 ± 0.4 μg l−1). We conclude that therapeutic effects from pharmaceutical contaminants need to be considered in risk assessment assays to avoid that important ecological effects from aquatic contaminants are systematically missed.


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