By Brian Bienkowski
for Environmental Health
News
A little bit of an
anti-depressant makes wild guppies less active, camp out more under plants and
freeze up for longer after something scares them, according to a new study.
The latest research
out of Australia adds to mounting evidence that one the world’s most widely
prescribed drugs—fluoxetine, most commonly known by the trade name Prozac—is
getting flushed into waterways and making fish act different. And different
isn’t good: The drug appears to be changing habits designed to keep fish alive
and reproductive.
Fluoxetine, used to
treat depression and anxiety, is the third most prescribed drug in the U.S.,
with about 28 million prescriptions annually. The drug is frequently found in
waterways by way of people excreting the drug or flushing pills.
Researchers collected wild adult guppies from Queensland, Australia, and put 60 fish in tanks with a low dose of fluoxetine, 60 in with a high dose and 60 in drug-free water.
After
28 days they started testing their behavior, specifically simulating a bird
strike and seeing how they responded. They used a fake heron, a bird that preys
on guppies, and had it strike into the center of the tank and then immediately
retract.
Fish exposed to
fluoxetine remained stationary (called “freezing”) for longer and spent more
time under plant cover. Both freezing and heading to plant cover are
anti-predator behaviors for fish and are crucial to their survival.
“There is no doubt
those are environmentally relevant treatment levels, and there’s no doubt there
are changes in behavior,” said Bryan Brooks, a professor of environmental
science at Baylor University who was not involved in the study.
The findings,
published in the journal Aquatic Toxicology, were sex-specific, with dosed
females spending more time under plant cover and dosed males becoming less
exploratory. These may seem small changes but they’re important for tiny fish
often preyed upon.
“Time and energy used in remaining stationary is diverted
from other fitness-related activities, such as foraging and finding mates,”
said lead author Minna Saaristo, a research associate at Monash University in
Australia, via email.
Saaristo said that
male guppies benefit from being “bold and exploring new territories” to find
mates, so any changes to their behavior could harm the overall fish population.
Anti-depressants, such
as fluoxetine, work by increasing serotonin function in the brain. This system
of the brain is similar across vertebrates, Saaristo said. Drugs that affect
human brains can and will affect fish brains.
“These drugs are
intended to alter behavior,” Brooks said.
More than a decade ago
Brooks and colleagues were the first to find anti-depressants
in fish. They reported fluoxetine and other drugs in every liver, brain and
filet tissues they tested from fish in a north Texas stream.
Since then multiple
studies have shown fluoxetine is not only accumulating in fish but altering
behavior.
In a landmark 2013
study, University of Wisconsin-Milwaukee researchers found that
fluoxetine-exposed male minnows were anxious, anti-social and aggressive—in
some cases killing females.
The lab work suggested that the drugs altered
how genes in the fish brains were expressed, or turned on and off.
The minnows
were exposed when they were a couple of months old and still developing.
Last March University of New England researchers
reported that male Siamese fighting fish were less aggressive
and bold after fluoxetine exposure.
Brooks said two of the
current study’s strengths were using guppies—which are not routinely
studied—and dosing at levels that are commonly found in waterways.
Brooks said he is
encouraged to see such studies specifically looking at fish behavior.
Pharmaceuticals are still tricky compounds that can “fall through the
regulatory cracks,” he said. Traditionally water contaminants—think pesticides
and metals—have been tested for toxicity but not the subtle behavioral changes
Saaristo and others are reporting.
It’s important to look
for behavioral changes to aquatic creatures, Brooks said, because our waters
increasingly have pharmaceuticals such as fluoxetine, and certain endocrine
disrupting compounds, that may not prove acutely toxic but alter behavior and
development.
Saaristo said the next
step for her research group is to tease out if there are indeed fish
population-level impacts from the fluoxetine exposure.
For questions or
feedback about this piece, contact Brian Bienkowski at bbienkowski@ehn.org.