Why bore your fish with a humdrum aquarium when you can house them in the Spillarium, a spherical 5 gallon tank that features color-changing LED lights and a spilling waterfall that plunges into a bigger fish's ceramic maw.
Though the MythBusters proved that goldfish don't really have a 3 second memory—they trained fish to swim through mazes and found that their times improved as they became familiar with the course—the Spillarium fish tank will constantly make your fish swim like its life depends on it. Lest that little fishy fall into a bigger fishy's mouth, carried to his cannibalistic fate by a stream of water that continually spills out of a hole in the tank.
The waterfall effect is designed to circulate water in the aquarium; the water is purified in the base and recycled back up into the sphere. But I like to think it's for keeping your fish on their best behavior. [Oh Gizmo]