In this pleasant and relaxing software experience, much like a real aquarium, you can customize your fish tank with different backgrounds, gravel styles, decorations, plant life, and of course, fish. Sit back, relax and interact with the fish. If you have to go away for a while, don't worry; you might even find a brand new fish when you come back! In My Aquarium, Wii owners can choose the fish that will live in their aquarium and what decorations they'll get to enjoy. You can choose the glass color, lighting, background design, style of gravel, rocks, or plant life for the world their fish will inhabit and can mix and match different fish in up to 6 individual aquariums. You can even send aquariums to friends using WiiConnect24 if they also have My Aquarium.
Source: The Developer Website.