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How Many Fish Does It Take to Lower Your Stress Level?

New research finds just the implication of aquatic life has an effect, but more sea creatures produce a greater impact.
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(Photo: ivosar/Shutterstock)

(Photo: ivosar/Shutterstock)

If exposure to nature is good for us, is exposure to more nature even better? An experiment conducted at a British aquarium finds some evidence that indeed it is.

"Fish tanks and displays are often associated with attempts at calming patients in doctors' surgeries and dental waiting rooms," marine biologist Deborah Cracknell notes. "This study has, for the first time, provided robust evidence that 'doses' of exposure to underwater settings could actually have a positive effect on people's well-being."

In the journal Environment and Behavior, Cracknell and her colleagues describe a study which took advantage of the "complete refurbishing and restocking of a large exhibit in the United Kingdom's National Marine Aquarium."

"As restocking was completed in three stages," they write, "it provided a rare opportunity ... to compare people's responses with different levels of biota in precisely the same setting."

The exhibit in question was contained in a 550,000-liter tank "viewed predominately through a single, huge acrylic window." In Condition 1, "it contained only seawater and artificial decoration." In Condition 2, it was partially stocked; most people who visited during this period viewed six species of fish. In Condition 3, it was fully stocked, with 19 fish species and three species of invertebrates.

"This study has, for the first time, provided robust evidence that 'doses' of exposure to underwater settings could actually have a positive effect on people's well-being."

In a preliminary experiment, researchers observed randomly selected members of the public and noted how much time they spent looking at the exhibit. Not surprisingly, they found people lingered longer the more fish were in the tank.

But the more extensive second part of the study featured 84 university students, who were randomly assigned to visit the exhibit during one of the three stages: unstocked, partially stocked, or fully stocked. After entering the aquarium, they had their heart rate and blood pressure measured, and reported their mood and level of emotional arousal.

Each participant then gazed at the exhibit for five minutes, during which their heart rate was "discreetly noted." After another five minutes of observation, their heart rate and blood pressure were taken again. Finally, they described their mood and reported how much they did or did not enjoy the experience.

"All three stages of exhibit restocking were associated with significant drops in blood pressure and heart rate, indicating that exposure in all conditions was calming and psychologically restorative," the researchers write.

Perhaps surprisingly, "the exhibit alone, although unstocked and containing only seawater and artificial decoration, appeared to be sufficiently interesting to confer some benefits," the researchers report.

That said, they found "the greatest drop in heart rate occurred in the fully stocked condition, and this drop was significantly different from the unstocked condition." What's more, "as stocking levels in the exhibit increased, participants' interest in the exhibit and willingness to watch it again significantly increased."

Participants' moods brightened, and heart rates decreased, with the number of sea creatures they observed.

They found no clear correlation between blood pressure levels (which decreased for all three groups) and the number of fish in the exhibit. The researchers suspect this reflects the fact that, while participants found the overall experience soothing, they simultaneously found the fully stocked tank to be stimulating.

The heart-rate decreases "were observed after a rest period, and so cannot be attributed simply to sitting quietly," Cracknell and her team write. "Most of these gains occurred within the first five minutes, with only diminishing returns following a further five minutes of exposure."

Even with this fall-off, the researchers found that, in general, "as duration of exposure increased, people became both more positive and calmer."

So even the inference of a natural environment (the empty but decorated tank) apparently reduced stress levels to some extent. But participants' moods brightened, and heart rates decreased, with the number of sea creatures they saw swimming.

The results suggest any exposure to nature is a positive thing, and getting truly immersed in a natural environment is even better. And this exposure needn't take place in a pristine wilderness: A built environment such as an aquarium will do just fine.

What's more, the fact the most robust effects were noted in the first five minutes suggests that the initial, calming dose of the natural world has the greatest impact on our health and happiness. So don't let a busy schedule be an excuse to pass up the park or avoid the aquarium. If you're suffering from stress, you'll benefit from even a brief visit with the fish.

Findings is a daily column by Pacific Standard staff writer Tom Jacobs, who scours the psychological-research journals to discover new insights into human behavior, ranging from the origins of our political beliefs to the cultivation of creativity.