The efficacy of animal-assisted therapy isn’t some sort of state secret; the news regularly fills in holes with fluff pieces about how Fido can keep you young or how research shows Mittens may help lower your blood pressure. But like every other kind of therapy, pet therapy isn’t ‘one size fits all.’ There are definite benefits—but if the benefits are outweighed by the drawbacks, the addition of a pet to your family can increase stress.

First, let’s take a look at the benefits. One of the obvious upsides to having a pet is simply that they’re there—pets provide companionship, which can be more than just a comfort to seniors who may be isolated and lonely. Not only do pets fill up the time, but as human friends pass away and adult children and grandchildren get busy and increasingly self-sufficient, pets provide a sense of purpose—they may not be the best conversationalists, but being responsible for any other life can renew a senior’s sense of meaning.

Of course, one of the significant drawbacks to having a pet is upkeep—dogs need to be walked and groomed, and even cats, which tend to be lower maintenance, require attention; additionally, they can get underfoot and be moving, breathing tripping hazards, and can knock over other objects and create messes. Even smaller rodents can trigger allergies. So what’s to be done?

Amazingly, it’s been shown in several studies that fish can have a notably beneficial effect on Alzheimer’s disease patients. Not only does easy access and exposure to an aquarium soothe aggression and depression in dementia patients, but it also has shown a marked improvement in appetite and food consumption at mealtimes, even leading to an overall, quantifiable increase in weight!

According to a study done by a nursing professor at Purdue University, participants in an Alzheimer’s study increased their food intake by an average of 17.2%. The same study “showed a decrease in the number of instances and the duration of behaviors such as wandering, pacing, yelling and physical aggression.”

Aquariums also provide a colorful and constantly moving source of entertainment and stimulation; because of its active nature, it is well-suited to the naturally short attention span of an Alzheimer’s patient. Even better—Alzheimer’s patients will get a boost of confidence from helping to feed the fish and seeing them respond to the arrival of food, and the huge number of aquarium accessories—from the ubiquitous deep-sea divers and castles to laughing Buddhas and popular cartoon characters like Spongebob Squarepants—means there’s no end to the possibilities when it comes to setting up a creative and colorful background for your fish.

The downside to fish, of course, is that they’re nowhere near as cute and cuddly as, say, a cat or a dog, but as the Purdue professor who headed up the aquarium study says, “[Alzheimer’s patients] might step on the cat’s tail or pull the dog’s hair,” whereas fish are “basically indestructible.”

While tanks require upkeep and regular maintenance, there’s no risk of “accidents” on the floor, and the last we heard there was no record of a fish chewing on expensive shoes. There’s no grooming, shedding, or walks on rainy days required. With such considerable benefits and fewer downsides, when it comes to your seniors, man may have a new best friend!