It's considered good feng shui to have moving water in your home, like in a fountain or aquarium. It helps activate the chi in a dry room, and our house was full dry rooms. It's even better to have fish, but only if they are kept alive. If they die you're immediately suppose go out and buy bigger, more expensive ones. Otherwise the gods will think you're a cheap-ass and your luck will be even worse than if you never had fish.
My mother believed in these aspects of feng shui but didn't want the burdens of real fish. Similar to the Forever Orchid, she found the Forever Aquarium. It was a cylindrical tower lined with blue cellophane and plastic seaweed. At the bottom was a propeller that would create an internal current that would make the plastic fish swim.
The tank is gone but last night I found the plastic fish. The four fish (including a Nemo) and three seahorses have wiggling tail parts, so their swishing would be believable to the feng shui gods.