First posted on 02-15-2013
Bolder, more gluttonous fish can damage aquatic ecology.
Water treatment plants only filter out so much material. Mineral levels, for example, are typically much higher downstream of treatment plants than they are elsewhere. That fact is driven by salt expelled by the body, but not captured during treatment.
A larger issue is the accumulation of pharmaceuticals passed through the body or dumped down the drain. Low concentrations of many different types of drugs are often found downstream of treatment facilities. Swedish scientists linked one such medication to aggressive behavior in perch.
Researchers at Umeå University in Sweden studied the effects of the anxiety-moderating drug Oxazepam on perch. Tomas Brodin, who led the study, explained, “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.”
The drug made fish less social, leaving their schools to hunt alone. The formation of schools is a defense strategy for fish, so loners took a greater risk of predation. Perch also ate their prey more quickly, a problem that could tip the balance of diversity in a stream.
“Perch that were exposed to Oxazepam lost interest in hanging out with the group, and some even stayed as far away from the group as possible.” Brodin said.
Since fish are an integral component of a stream’s food web, alteration of their natural habits could change the ecosystem. The researchers predicted the possibility of consequences over time, such as algal blooms, in waters where fish behaviors changed dramatically.
Researchers said that fish in the study accumulated Oxazepam in their muscle tissue in concentrations comparable to what they found in wild perch. They felt it likely that perch in streams could already be experiencing behavior changes similar to the test fish.
Many more drugs with the same function as Oxazepam are found in the tailwaters of sewage treatment plants worldwide. The use of medications is on the rise, so we could be on the cusp of a considerable shift in the behavior of aquatic animals.
Jerker Frick, an environmental chemist said, “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.”
Brodin and his team admit that more study must be done before drawing long-term conclusions, but they say that their discovery points to what may already be underway in waters around the globe.
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