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Stockholm: Medicinal
drugs that end up in the world's waterways after being excreted,
flushed and treated at wastewater treatment plants may
unexpectedly alter fish behaviour, says a new finding.
Tomas Brodin and colleagues from Umea University in Sweden
discovered that the a wild European perch, a fish species ate
faster, became bolder and acted less social after being subjected
to an anxiety-moderating drug, known as Oxazepam.
The psychiatric drug is used to treat anxiety in humans. But,
Oxazepam residues often wind up in natural aquatic systems,
downstream from sewage treatment plants, where their effects on
eco-systems have been unknown, the journal Science reports.
Now, Brodin and the other researchers have dosed wild perch with
amounts of Oxazepam equivalent to those found in Sweden's rivers
and streams, and their results suggest that even small amounts of
the drug can alter the behaviour and the foraging rates of these
fish, according to an Umea statement.
"While alone, fish that were exposed to Oxazepam dared to leave
safe refuge and enter novel, potentially dangerous areas,"
explained Brodin.
"In contrast, unexposed fish stayed hidden in their refuge. The
exposed fish seemed much less stressed and scared, behaving calmer
and bolder."
Perch that were exposed to the drug also devoured their food
quicker than unexposed fish-a behavioural quirk that the
researchers say could alter the composition of species in the
water and lead to ecological events, such as increased algal
blooming, over time.
Since fish are generally integral pieces of their food webs,
changes in their eating patterns could disturb ecological
balances, according to the researchers.
The fish that were given Oxazepam during the study also became
anti-social, distancing themselves from other perch and putting
themselves at greater risk of predation.
"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," explained Brodin.
The fish in the study accumulated concentrations of the drug in
their muscle tissues that were comparable to those found in wild
fish, said the researchers.
But, a veritable cocktail of drugs can be found in waterways
worldwide, making the discovery of Oxazepam's effects on fish that
much more important.
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