Anti-depressants disrupt fish's brains

3 July 2014 by Alex Peel

Drugs designed to ease the symptoms of mental health problems such as depression, obsessive compulsive disorder and post-traumatic stress can have major disruptive effects on aquatic animals' brains, say scientists.

PillsAnti-depressants are some of the most commonly prescribed drugs in the world. In 2012, there were more than 50 million prescriptions of the drugs in the UK, and in some towns and cities as many as one in six of us are taking them.

In recent years, researchers have found increasing concentrations of the drugs in rivers around the world. Most of them find their way into waterways via sewage and waste water systems, from human waste or from people flushing unwanted prescriptions down the toilet.

A suite of new research, published in a special issue of the journal Aquatic Toxicology, points to mounting evidence that they could be damaging aquatic species.

Researchers have found that fish exposed to tiny concentrations of the drugs in the laboratory can become more aggressive and less cautious.

In other aquatic species, their ability to find food and reproduce was affected, their behaviour patterns were altered, and some became more attracted to light. There is also evidence that the drugs may damage the ability of cuttlefish to camouflage, and disturb genes controlling the brain function of shrimp.

At the moment, it's almost impossible for regulators to work out what is a safe level for these drugs in the environment

- Dr Alex Ford, University of Portsmouth

"In the 90s there was lots of concern about the so-called gender-bending properties of contraceptive drugs that were finding their way into our rivers," says Dr Alex Ford from Portsmouth University, who edited the special issue.

"There is now substantial evidence from laboratory tests that anti-depressants can affect animals' behaviour and basic functions even at the very low concentrations that they would be likely to encounter in the wild."

Most anti-depressants work by increasing the availability of the mood-influencing chemical serotonin in the brain. Many aquatic creatures also produce serotonin and appear to be sensitive to the effects of the drugs.

In one experiment, a shrimp was placed in a test-tube which was then lowered into a tank with cuttlefish. Whereas cuttlefish not exposed to the drugs would soon give up on the unobtainable snack, those exposed to the anti-depressant continued to slam into the tube, wasting vital energy in the process.

In another, a group of male crayfish became more aggressive - fights lasted longer and rates of female mortality rose sharply.

For now, difficulties in accurately monitoring exposure levels and animal behaviour in the wild are proving a significant barrier to understanding the threat of anti-depressants in the real-world environment.

Signal crayfish

Signal crayfish.

And some scientists caution that the effects of the drugs need to be tested at a variety of doses before more robust conclusions can be drawn.

"As a proportion of the whole US population, there are probably as many people taking these drugs now as there are on the contraceptive pill," says Ford.

"At the moment, it's almost impossible for regulators to work out what is a safe level for these drugs in the environment."

He warns that these problems are not unique to anti-depressants. Humans consume hundreds of different drugs every day, and many are likely to find their way into sewage and, eventually, the environment.

There has been talk of increasing the requirements on sewage treatment plants to remove the chemicals, but the costs of doing so make it unlikely to happen anytime soon.

Many countries are instead focusing on those drugs which go unused, encouraging people to take unwanted prescriptions back to their pharmacist instead of flushing them away.

"Like many people, my kitchen drawer at home is full of drugs that are long out of date and no good to anybody," says Ford. "We don't want to stop people taking drugs, they obviously save countless lives and bring all sorts of benefits to people, but we need to manage the way that we get rid of them."

Correction: This article originally implied that cuttlefish was a fish. It has since been pointed out that, despite its name, it is a mollusc. It also incorrectly described serotonin as a hormone - it is a neurotransmitter which carries messages around the brain. We apologise for any misunderstanding caused.


Alex Ford, 'From gender to brain benders (and beyond!)', Aquatic Toxicology, 2014.