Asocial fish by psychotropic drugs in rivers

Psychotropic residues in rivers make fish more courageous and antisocial

15/02/2013

The residues of psychotropic drugs enter the wastewater into our rivers and can lead here even in the smallest doses to sustainable behavioral changes of fish and other aquatic organisms, scientists of the Swedish Umeå University in the journal „Science“. The animals react „Strange even at low concentrations of the drugs in the rivers, suggesting that the psychotropic drugs may affect fish behavior and ecology in small doses“, The researchers write about Tomas Brodin from Umeå University.

According to the Swedish scientists, "Hundreds of different medicines are capable of hatching through conventional treatment plants and then find their way back to our waters". Researchers at the University of Umeå explained that "the many medicines in the rivers and streams have an impact on aquatic life." It is already known from previous studies that "high concentrations of pharmaceutical residues in the waters have an influence on aquatic organisms". Now the Swedish researchers have been able to show that even very dilute concentrations of psychotropic drugs lead to serious behavioral changes in fish - they became more courageous, but at the same time showed a less sociable (in part antisocial) behavior.

Residues of the drug oxazepam in the waters
The Swedish scientists have according to their own information already „a few years ago, the psychoactive drug oxazepam (a group of diazepam) in water samples from the Fyris River that flows through Uppsala - the fourth largest city in Sweden“, demonstrated. Oxazepam belong „to a class of drugs that make the neurons less excitable and slower“, the researchers report. The transmission of signals in the brain is inhibited. Oxazepam-based psychotropic drugs are one today „essential“ Part of the treatment of panic attacks and other severe anxiety disorders, write the Swedish scientists. The burden of waters with such drugs is included „no particular Swedish problem“, continues the main author Tomas Brodin. Since the psychotropic drugs accumulate over time in the tissue of the fish, even low concentrations should be critically evaluated in the long term. According to the researchers, this was the case with perch from the river Fyris „Oxazepam concentrations up to six times higher in fish muscle than in water“, report Brodin and colleagues.

Fish under the influence of psychotropic drugs show significant behavioral changes
The research team of the University of Umeå has investigated in its current study, the effect of the residues of psychotropic drugs in the body of water on the organism of fish. They tested this on three different groups of juvenile perch (perch-juvenile). One group was raised in an aquarium with twice the concentration of oxazepam as in the river Fyris, another at 500 times the concentration, and the third in water-free drug residue. The scientists observed „three striking changes in perch behavior that were exposed to oxazepam.“ Thus, the perch laid by the psychotropic drugs behavior as „Swarm fishes“ from. This „social behavior that holds the fish shoals together and protects them from predators“, Under the influence of the drugs, it was significantly lower and the fish instead swam more often solo, write Brodin and colleagues.

Increased risk-taking under the influence of the drugs
Second, fish exposed to very high levels of psychotropic drugs had a significantly increased risk appetite. The perches became bolder and more daring „as their sober peers jump over a flap in the aquarium into a new environment“, This is the finding of the Swedish research team. The third conspicuous behavioral change, according to the researchers, concerned the dietary behavior of the fish. Both groups under the influence of psychotropic drugs therefore showed a much greedier feeding behavior, but also proved to be more efficient feed funders and better hunters of water fleas.

Unclear consequences of behavioral changes in perch
In the context of their study, the scientists were unable to clarify clearly how the behavioral changes due to psychopharmaceutical residues affect the fish in their natural environment. Both positive and negative effects are conceivable here. For example, fish's avidity could lead to drastic decimation of water fleas, possibly threatening algal blooms, depriving water of oxygen and, in the worst case, causing the fish to die, write Brodin and colleagues. On the other hand, "more efficient feed procurement may also increase the fish population faster." The more courageous behavior, however, as well as the stronger inclination to anti-social unilateral actions, can also lead to the fish frequently falling victim to predators. This depends heavily on whether the perch are the largest predatory fish in their environment, so the conclusion of Brodin and colleagues.

Reduction of drug residues in waters required
Their study highlights the urgent need for improved wastewater treatment, the Swedish researchers emphasized. Comparable behavioral changes as for perch are to be expected also with other fish. In addition, the residues of the drugs on the drinking water increasingly reach humans. Here, for example, a study by Jacobs University Bremen on the pollution of drinking water in Berlin in 2010 showed that there were sometimes alarming strains with the MRI contrast agent gadolinium. This contrast agent could also be used as an indicator for the drinking water load with other drugs, the Bremen researchers reported about two years ago and referred to possible health risks for the population. (Fp)

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Image: Roger Mladek