i may be wrong but i always thought hardware is where the money is made.... at least in singapore...
because the common fishes are so cheap i can't imagine how they can earn from there, taking into account, food, medicine, water change, quarantine, some deaths etc
I definitely agree that hardware is where the money is at, which is also why 50% of tung choi st is dedicated to the stuff these days pushing a lot of the actual fish stores out...