Why is that aquariums are such popular screensavers? I guess it has something to do with the fact that your screen makes the perfect looking glass into the colorful world of exotic fish.
SereneScreen Marine Aquarium is one of the most realistic you'll ever see, bringing a stunning underwater virtual world to your PC. The screensaver is full of coral and exotic fish, with air bubbles and random darting movements adding to the realism. It also features an on-screen clock, which you can toggle on and off.
The fish are modeled in 3D for maximum effect and the screensaver can be displayed on multiple monitors and even wide screen displays for a truly spectacular show. There is an abundant amount of fish and the developer has just added to them with the 'Clearfin Lionfish' and 'Achilles Tang', taking the total number of species to 28. The only slight drawback is that this screensaver is a little more heavy on your CPU than most due to the 3D rendering.
As visually impressive as SereneScreen Marine Aquarium is, you might eventually get bored of watching them just swim about all day long.