Insaniquarium Deluxe is a strategy puzzle fish tank management video game developed by Flying Bear Entertainment and published by PopCap Games. If you want to have a virtual aquarium on your Mac, where you can feed the fish and customize it with new species of plants and aquatic animals, you can check this list of alternatives. Unfortunately, at the moment, the developer hasn't released a version of Insaniquarium for Mac.
For Windows users, I think you are able to download Insaniquarium Deluxe for Free (trial version). Basically, I am a Mac user and I found this amazing tutorial on how to play Windows Steam Games on Mac.