They studied physiological effects the tank had on people as they looked at it, and discovered that as more fish were added, heart rates and blood pressure dropped. People reported having better moods after looking at the exhibit.
"Even watching a normal tank — the light and the movement of the artificial seaweed — was quite relaxing for people," said Deborah Cracknell, lead researcher at the National Aquarium, in a statement. "But when we added fish, it definitely did make a difference."
It's not that surprising a result — aquariums are known to be calm and enchanting places. Good evidence of that can be heard in the music from Camille Saint-Saens inspired by aquariums. But it does add to the vast body of research that says people can physically improve stress levels by escaping the grind and observing nature.
Loads of studies have shown that green space — like gardens or parks — has similar physiological effects, and there have been other studies done to show that visitors to dentist offices and elderly homes will have lower blood pressure and reduced anxiety if there are fish tanks present.
There's also evidence that the type of marine life present in the tanks can make a difference. Authors of the study suggest that people were more affected by images of colorful, tropical fish and higher levels of biodiversity.
"I can see that this could be used in a hospital setting," Cracknell said. "Even if you couldn't have a physical tank, maybe you could have a video or a link to a real tank."