Studies show and my personal experience confirms that watching fish calms and soothes oneself. I’ve seen several medical offices which displayed a beautiful aquarium in the waiting room. And the reason is that people tend be stressed and anxious while waiting for their turn to be consulted, and watching fish swim in their aquarium reduces the stressful minds. This article http://journals.sagepub.com/doi/pdf/10.1177/0013916515597512 contains a more in-depth description of the phenomenon.
I don’t know how fish feel about this human behavior, but I know that my fish are always happy when I am around. They come close to the glass and wiggle the tail just like puppies. It may be food on their mind, but their attitude makes me feel grateful for having them.