Are we drugging our fish?

Pharmaceutical drugs in rivers are changing how they feed, reproduce and evade predators

Are we drugging our fish?

by Angling Times |

ANTI-depressants being washed into our waterways are changing the behaviour of fish and affecting their growth, reproduction and survival rates, new research shows.

Traces of common pharmaceuticals taken by humans are difficult and expensive to cleanse from sewage, meaning they are increasingly found in our rivers.

Scientists in Australia tested the effects of fluoxetine (also known as Prozac) on 3,600 tank-kept fish and found zombie-like shoal behaviour that may make them far less inclined to escape predators.

Scientists from Sweden are also planning to test the impact of anti-anxiety drugs on pike, perch and roach in the wild.

Professor Bob Wong, who led the Australian research, said:

“Pharmaceuticals pollutants can affect ecologically important behaviours, such as the ability to find food or mates, or avoid predators. Such disturbances can have a direct bearing on reproduction and survival.”

Across the world more than 600 different pharmaceuticals have been found in waterways, Professor Wong added, and the Australian study, published last month, replicated the typical wild concentrations of anti-depressants such as Prozac, and tested the impacts on fish.

The experiment

The 3,600 fish were kept for two years in tanks containing either freshwater, water with typical wild levels of fluoxetine, or higher levels that might be found near sewage outlets. Scientists then placed one fish at a time into a fresh tank with a white background and a dark patch in one corner to simulate a hiding spot. The drug-free fish showed a range of behaviours, from darting about to being more inactive, while the Prozac-exposed fish showed half as much variation in activities and did “not have their individuality any more.”

Professor Wong added:

“There is evidence from research conducted in Europe that pharmaceutical pollutants are showing up in species of fish targeted by anglers. We also know that pharmaceutical pollutants can affect the behaviour of important angling species, such as perch and various salmonids (salmon and trout).”

Should we be worried?

Asked whether this was an environmental cause for concern more generally, Professor Wong said:

“Yes. Vast quantities of the medicines we take or give to our pets and livestock can end up in the environment and many of the receptors targeted by these drugs are ‘evolutionary conserved’, meaning medicines designed for humans or for our pets or livestock can also impact on wildlife. Studies have reported all kinds of behavioural, physiological and morphological disturbances. What’s more, there is potential for such effects to cascade beyond their initial disturbance, with consequences for the entire ecosystem.

“Here in Australia, pharmaceuticals are turning up in the tissues of aquatic invertebrates. These are consumed by spiders living on the water’s edge, so the spiders also end up being exposed. It has been estimated that platypuses in some urban streams in Melbourne could be consuming as much as 40 per cent of an adult dose of antidepressants every day!”

Faster-growing perch, clumsy pike

Professor Tomas Brodin, of the Swedish University of Agricultural Sciences, is currently planning an experiment on wild perch, pike and roach. He told Angling Times:

“In the lab we have seen anti-anxiety drugs make perch less social, more risk-taking and more active.

“This makes them forage more efficiently and grow faster. But it also makes them much more vulnerable to predators such as pike. Luckily for perch, pike are also affected by the medicine and have a significant increase in failed attacks.”

Asked whether anglers might notice differences, Professor Bodin added:

“Our results suggest fish exposed to anti-anxiety pharmaceuticals might be more prone to attack baits, but they will be less accurate in their strike. The exposed fish will probably also be less stressed out by disturbance on the banks!”

What’s being done about it?

UK water companies came together to form the Chemical Investigation Programme a decade ago, though there is still no single process which removes all pharmaceuticals from wastewater. Individual treatments, which use a lot of energy and chemicals, are also not 100 per cent effective.

Angling Times contacted trade body Water UK and all individual English water companies for comment. Thames Water said it would be watching the Somerset trial with interest (see panel below) and that there was no danger of pharmaceuticals entering the drinking water supply.

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