Sega Toys' digital pocket aquarium avoids the work and spitefulness of a real aquarium. Of course, it also means that you're wasting your time on something that isn't even alive!
As the little guy grows, so does the world around him or her–the scrolling map widens accordingly to reveal new areas of the underwater world. There are also three mini games you can play with your pets, which are sure to boost mutual affection. The Handheld Aquarium offers countless hours of fun (not to mention responsibility training) for all ages.
It is, at least, far more tasteful than most Tamogotchi-like toys. But are there apartments that disallow fish? Let's have a pocket unicorn, or something else prohibited by the rental contract. ("Tenants shall not keep or house animals of any kind whatsoever over 25lbs in weight, including dogs, extraordinarily overweight cats, and space narwhals.")
Handheld Aquarium from Sega Toys [Japan Trend via Random Good Stuff]