Monday, February 18, 2013
A new study shows that medicine designed to help humans suffering from anxiety disorders and insomnia also changes the behavior of wild perch, but outcomes for the fish appear to be far less positive. For them, exposure to the generic drug Oxazepam causes hyperactivity, increased appetites, and anti-social behavior. Taken together, these new behaviors put perch in greater danger of being eaten by predators that can more easily hunt lone fish that chose to forgo the safety of a school.
Swedish researchers discovered changes in the behavior of wild European perch after exposing them to different concentrations of the medicine over a period of seven days. At the lowest concentration–three times higher than what has been reported in surface waters in both the U.S. and Europe–the fish moved more, ate more aggressively, and ventured alone into unfamiliar places. And the effects were even more noticeable at concentrations up to 1,500 times higher than existing levels.
Behaviors like these that change a species' ability to catch food or avoid being eating can also have long-term consequences for other organisms living in the same habitat. In the case of the perch, aggressive feeding could cause a dip in the population of zooplankton, a staple of their diet. Because zooplankton feed on algae and keep it from blanketing lakes and rivers, hungrier perch could mean less oxygen and sunlight for other aquatic life.
In addition, researchers found that Oxazepam builds up in the perch. Fish living in the Fyris River in central Sweden had more than six times the natural concentrations in their muscle tissue when they were tested at the start of the study. It is unclear what impact this has on predators that feed on the perch.
It is also unclear what these results mean for fish living in waters with lower concentrations of Oxazepam, but for longer periods of time than the study's seven days. These results, though, join a growing number of studies that suggest that pharmaceuticals in waterways can affect the biology and behaviors of aquatic animals.
Brodin, T., Flick, J., Jonsson, M., and Klaminder, J. Dilute concentrations of a psychiatric drug alter behavior of fish from natural populations. Science. Vol. 339 no. 6121. DOI: 10.1126/science.1226850. Publication date: 15 February 2013.
Written by: Anjanette Riley, IISG Science Writer