Drugged up fish become greedy and bold


The behaviour of perch changes in the presence of drugs in the water (photo credit: Bent Christensen, Umea University)

Modern medication is a god-send for many people who are suffering illness and disease. Prescription drug use is also booming across the world but not all drugs administered stays in the body. A large proportion goes through the body to end up in waste-water and some will pass through water treatment to end up in the natural environment.

A new study shows that anxiety-reducing drugs that end up in rivers and lakes can make fish more bold and they also become ravenous, eating at much quicker rates that normal.

The study by Umeå University researchers in Sweden has been published in the prestigious journal Science. It’s the first time that fish behaviour has been observed to be modified by drugs reaching the natural environment.

The researchers looked at  the impact on perch of the anxiety-moderating drug Oxazepam. At concentrations of drug found in the freshwater environment of densely populated areas the differences were noticeable.

Normally, perch are shy and hunt in schools. This is a known strategy for survival and growth. But those who swim in Oxazepam became considerably bolder,” explains ecologist Tomas Brodin, lead author of the article.

This led the affected fish to leave the social confines of the shoal and look for food on their own. This boldness means that the perch also left the protection of the shoal where there is safety in numbers. This could have consequences for predation rates of perch populations.

The fish affected also ate more and more quickly which could have an impact on the eco-system that they live in by affecting community balance.

We’re now going to examine what consequences this might have. In waters where fish begin to eat more efficiently, this can affect the composition of species, for example, and ultimately lead to unexpected effects, such as increased risk of algal blooming,” says Brodin.

Higher concentrations of the drugs used in the study are found in surface waters downstream of sewage treatment lagoons. With drug use expected to increase around the world in coming years there could be unintended consequences for the freshwater environment.

The team do not suggest reducing medication but advise that there could be a need for better designed waste-water treatment system to reduce the amount of pharmaceuticals getting into the wider environment.

As environmental chemist Jerker Fick explained, “The solution to the problem is not to stop medicating ill people but to try to develop sewage treatment plants that can capture environmentally hazardous drugs.”



Posted in Freshwater and tagged , , .
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