Aquazone Seven Seas Deluxe features an amazing array of 40 stunning Fish, Sharks, Turtles, and Jellyfish making it one of the most complete aquarium solutions out there. The colors and swimming actions are incredibly realistic and you can pick and choose species to fit your tastes.
Apart from the 40 fish on show, Aquazone Seven Seas Deluxe includes 20 different tanks each with unique plantlife and coral and the realism even includes day and night. To make things even more realistic, Aquazone Seven Seas Deluxe lets you feed your fish with "digital food" and even tap on the glass to make them move around a bit. If you want to spend some time following a specific fish, you can use a Virtual Fish Cam which zooms-in on a selected one and follows it around for a while.
The only slight problems you might find in Aquazone Seven Seas Deluxe are that some tanks are not big enough for certain species of fish (and you're warned when selecting them when this is the case) and also, the program does hang for a few seconds when you change the preferences to add new fish or change the tank.
For stunning aquarium realism and the widest range of fish available anywhere, you can't do much better than Aquazone Seven Seas Deluxe.