[Shinsa]

I don't know if this has come up yet, but how about having the fish actually grow? Have the selected fish start at a young age, and watch as they mature. This could be done at a selectable time scale. Maybe even have the fish lay eggs? Mating? NAH! That's getting a bit too real!!

And if the option to feed them is there, then how about the fish dying off? Nothing morbid, maybe just fade away, and now a fish is missing?"Hey! Where'd my favorite Powder Blue Tang go? Uh oh, I forgot to feed them..."

I remember a program on my old Apple IIe called "Little Computer People" or something like that. You needed to have a daily interaction with this program or the little guy would get ticked off. And this was about 15 years ago!