Small virtual fish bowl to sit on your desktop.
Brighten your day with a friendly fish to swim around and occasionally beg for food!
See how good a caregiver you are by ensuring you keep up with his meals (or make him immortal if you just want companionship).
Vary it up with alternate fish and alternate bowls.
Stressed out and need someone to take it out on? Well, far be it from us to encourage harm to a poor defenseless fish, but if you hunt around in the menus enough...
And he'll even help with your taxes. [Ed. - Fish not qualified to provide tax advice]