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Wild Fish Can Become Addicted to Methamphetamine in the Water

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Scientists have shown that brown trout are at risk of becoming addicted to methamphetamines that enter the water supply. The new study is published in the Journal of Experimental Biology.1

Pharma pollution in freshwaters

A growing amount of research has demonstrated how pharmaceuticals – designed for treating human disease – can accumulate in water supplies, exposing aquatic organisms to their effects. A 2013 study published in Science found that dilute concentrations of the anxiolytic Oxazepam could alter both the behavior and feeding rate of wild European perch. Chronic exposure at environmental concentrations to six pharmaceutical families was detected in eight different fish species by the US EPA 2008–2009 National Rivers and Streams Assessment. Concerns are therefore mounting as to the full impact of pharmaceutical pollution on aquatic life.

Illicit drugs, those that are illegal to make, sell or use, have also been detected in waterways. Users of such drugs excrete them into sewage collections systems, where the substances can then enter wastewater treatments plants that are unable to filter out such contamination. Eventually, the contaminants enter freshwater ecosystems at low – but detectable – concentrations. Illicit drugs are often addictive when consumed by humans, but it is unclear how they might affect aquatic organisms in the concentrations at which they have been detected in the environment. Now, a new study by researchers at the Czech University of Life Sciences and the University of Southern Bohemia has shed some light.

A method to test meth addiction in fish

Dr. Pavel Horký and colleagues explored whether a species of brown trout (Salmo trutta) was at risk of addiction to the recreational drug methamphetamine. "Brown trout is a globally important species that is native primarily in Europe with a range extending to western Asia and North Africa but with naturalized populations on all continents except for Antarctica," Horký says in an interview with Technology Networks. "It has also been employed as a model species in toxicology." Using this model organism for the study therefore yields data that are broadly relevant to numerous ecosystems.

Methamphetamine has been detected in freshwater rivers at concentrations between hundreds of nanograms per L-1 and 25 µg per L-1. This variation is attributed to human events, such as weekend socializing, or music festivals, Horký explains. For this work, the team opted to test an intermediate concentration of 1 μg per L-1.

A sample of 120 trout were divided into two groups. One group was isolated in a water tank laced with methamphetamine for eight weeks, and the other group acted as a control, isolated in a tank without methamphetamine for the same duration of time. After the eight-week period, the trout were transferred to a tank with clean water for 10 ten days to simulate withdrawal. Forty-eight hours after transferring the trout to the clean tank, the researchers commenced behavioral studies, whereby the fish were exposed to a two-current choice flume.

"The choice arena consisted of two flows – one was dosed with the same environmentally relevant concentration of methamphetamine and the other one was a control. Preference for methamphetamine during a simulated withdrawal period was considered an indicator of addiction," Horký says. The choice flume is a reliable method, he adds, and is widely used to study how aquatic organisms perceive and respond to chemical cues in the environment, including avoidance or preference towards toxicants.

Wild fish can become addicted to methamphetamine

In the behavioral studies, the trout that had been exposed to methamphetamine-contaminated water for eight weeks displayed preference for the water that contained the drug during the first four days after being transferred to the choice flume tanks. The control group did not display such preference.

In addition, the trout also demonstrated signs of lower activity than the control group. Post-mortem analyses of the methamphetamine-exposed trout’s brains revealed biochemical changes that were related to the observations of withdrawal symptoms. "Significant differences (both up- and down-regulated signal intensities) between control fish and those experiencing the withdrawal period during depuration gradually decreased from 210 signals (substances) during the 2nd day of depuration to 36 substances during the 10th day," the authors write in the publication.

The study outcome concerns Horký and colleagues: "Drug reward cravings by fish, as was documented in our results, could overshadow natural rewards like foraging or mating that provision homeostatic and reproductive success. The elicitation of drug addiction in wild fish could represent another example of unexpected evolutionary selection pressure for species living in urban environments, along with ecological side effects of human societal problems within aquatic ecosystems," he says. There is a need to explore the withdrawal effects of methamphetamine observed in the experiment in natural ecosystems, which will be the next step for this work.

As described previously, illicit drugs are not the only contaminant that can be found in waterways. To this end, Horký emphasizes the need for society to confront its potential overuse of prescription medications: "Current research from teams around the world undoubtedly shows their adverse impact on ecosystems, which in turn can influence humans. Everybody should think about it and use medicines responsibly, just in case of real need," he concludes.

Dr. Pavel Horký was speaking to Molly Campbell, Science Writer for Technology Networks.


Horký P, Grabic R, Grabicová K, et al. Methamphetamine pollution elicits addiction in wild fish. J. Exp. Biol. 2021;224, jeb242145. doi: 10.1242/jeb.242145.