Last year, while standing in the middle of the marine life aisle at our local pet store, my children pleaded for a fish tank. “They’re easier to take care of than a dog,” they wailed. “We’ll feed them, and clean their water, and take them for walks." I had heard it all before, but I’m obviously easily influenced by their adorable facial expressions. So, that afternoon, I left with three aquariums: two small, five-gallon tanks suitable for only a few fish and the other a large 50-gallon tank that, at first glance, looked like it could’ve housed Dory and her entire extended family. I placed the tanks in various rooms where everyone could enjoy them. Although they were mainly meant for my kids to marvel over, I think I’ve benefited most from their presence.

I was immediately drawn to the subtle water sounds, colors, and serenity of the environment. I was intrigued by how the fish came to the edge of the tank and followed me as I passed by. I’ve also found that they’ve had a positive impact on my mood. I’m calmer and feel less stressed after sitting with Ms. Cupid, Raphael, Bob, and their various companions. What I thought was just a coincidence is actually a recognized approach to mental well-being called “aquarium therapy.”

Aquarium therapy, while not an official concept, is part of a larger field called animal-assisted therapy (AAT). AAT includes the use of certified therapy animals as a part of a therapeutic plan.

Studies have found that aquarium-watching helps reduce stress and anxiety, increase feelings of relaxation, and decrease heart rate and muscle tension. In fact, staring at a fish tank for as little as five minutes has an almost hypnotic effect, calming us down because of our genetic predisposition to regard some natural environments as non-threatening and essential to survival.

“The importance of viewing nature, especially animals, appears to be deep-seated into the human psyche,” says Alan Beck, professor and director of the Center for the Human-Animal Bond at Purdue University. Humans understanding and appreciation for the natural world, and our preference for natural environments, could be the product of biological evolution. He refers to the attraction as the biophilia hypothesis, coined by American biologist E.O. Wilson, which describes our innate tendency to focus on life and lifelike processes.

“Viewing nature in the form of aquarium fish is nature on demand,” Beck adds. And the benefits, which are still being explored, appear to be numerous.

In one recent study, watching an aquarium display for ten minutes was linked to noticeable long-term reductions in blood pressure and heart rate. The study assessed the physical and mental responses of 112 random participants to a tank containing varying amount of fish. The findings showed that people relaxed even when the tank was empty, with heart rates reducing by as much as 3 percent. As fish were added, the benefits increased with heart rate and blood pressure lowering up to 7 percent and 4 percent, respectively. The more fish, the more people’s moods improved too. People were happier.

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“Overall, we found that images of tropical exhibits containing large numbers of different species were usually preferred to, and were perceived as more restorative than, images of exhibits with few species/animals,” says Deborah Cracknell, lead author and an independent researcher affiliated with Plymouth University and the University of Exeter. “When using a large, live aquarium exhibit, we found that people's improvement in mood—and drop in heart rate—was greater when they viewed more, versus less, fish.”

In a previous study, conducted by the Center for Human-Animal Interaction at Virginia Commonwealth University, investigators looked at the effect of an aquarium on pre-treatment anxiety, fear, frustration, and depression in electroconvulsive therapy (ECT) patients. Forty-two patients were rotated between rooms with and without fish tanks while awaiting treatment. While no participants showed significant changes in their blood pressure and heart rate, the average patient experienced 12 percent less anxiety in the presence of an aquarium.

The effects of these little gilled therapists aren’t limited to mental health either. A 1999 study, conducted at Purdue University, revealed that aquariums can improve Alzheimer’s patients’ eating habits and behavioral patterns. The study followed 62 patients in three healthcare facilities for 16 weeks. Researchers examined how participants behaved before, during, and after the introduction of a 30- by 20-inch aquarium with eight large, colorful fish. The results showed that the tanks increased food intake by 21.1 percent and increased the patients’ level of attentiveness as well.

“People with advanced Alzheimer’s disease are often so agitated that they don’t stop for meals and lose weight to the level of endangering their health,” Beck says. “Fish tanks hold the attention of these patients and they significantly gain weight and are less of a burden for others.”

Additional studies confirm that watching fish in an aquarium can be effective in reducing anxiety in patients awaiting dental surgery. Aquariums can also help adults and children with autism and ADHD.

“With increasing scientific evidence to support the effectiveness of animal-assisted interventions, more hospitals, nursing homes, and schools are welcoming therapy animals into their facilities,” says Steve Feldman, executive director of the Human Animal Bond Research Institute (HABRI). “We often think that this activity is limited to dogs, but scientific research also demonstrates the therapeutic benefits of aquarium fish for a number of health conditions and populations.”

Aquarium fish might be the right choice for some because, as Feldman explains, in addition to the health benefits that aquariums can provide, they can be easier to maintain. They’re also ideal for those who don’t have the time, money, or means to reach the real "natural" environments that have calming benefits.

“Lost in watching fish as they swim with great beauty, without predictability, holds our attention and gives us time to relax,” Beck says. So, while dog might be man’s best friend, don’t rule out a buddy with scales.