Fish On Human Drugs Alter Their Behavior
February 15, 2013

Drug Residue In The Water Changes Fish Behavior, Making Them Bolder And Gluttonous

Michael Harper for — Your Universe Online

Ecosystems are complicated and tightly integrated systems. One small change to any part of the system can and will affect another part of the system further down the line. As humans, it´s sometimes easy to forget that we´re also a part of a larger ecosystem and that even the tiniest of actions can affect another living thing somewhere down the line.

A recent study describes this sort of cause and effect chain reaction, finding that the drugs leaving our system end up medicating fish in the sea.

According to ecologist Tomas Brodin, lead author of this study, our bodies don´t absorb medicines with 100% efficiency. Traces of these medications leave our bodies as waste and therefore end up in wastewater. Low concentrations of certain drugs have been found in wastewater treatment plants, causing scientists such as Brodin to investigate what effect, if any, these medicines have on fish.

In particular, Brodin studied the effects of the anti-anxiety drug Oxazepam on perch. This medicine is usually prescribed to patients who are experiencing withdrawal from alcohol and works by slowing down activity in the brain to quell anxiety.

Brodin and team found that fish who live in waters where higher concentrations of this drug were found acted quite differently than normal.

“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,” explained Brodin.

Rather than swim around with their school, these perch became less social and began striking out on their own to find food. This behavior is actually quite dangerous for these fish, as swimming in a pack helps protect them from other, predatory fish.

Brodin also noticed that the exposed perch did seem less “stressed and scared” than those fish that had not been exposed to the drug.

These fish also exhibited a different kind of behavior: They ate much more quickly than normal. As fish play their own important role in their ecosystem, these changes could dramatically disturb the ecological balance underwater.

“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,” explained Brodin.

Sweden isn´t the only place where the water has been tainted by our human drugs. Surface water all over the world has been found to contain human medicines, and not just the water surrounding sewage plants. What´s more, scientists expect that we´ll continue medicating ourselves, meaning more drugs in the water. Though he´s not the only scientist to note this trend, he´s only studied the effects of one drug on one type of fish in one part of the world.

When looked at on a broader scale, the ecological consequences could be severe.

“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,” suggested environmental chemist Jerker Fink.

The related report appears in the today's issue of the journal Science, which is published by AAAS, the nonprofit science society.