So, I've never done aquaponics before, but I've read and watched about it online, and I'm interested in exploring my options as an city dweller.

I've read that in a 55-gallon drum, up to 12 adult tilapia can live, and that a good ration is one male to four or five females.

Now, here's my dilema: if I live in a second story apartment, I am worried that the concentrated weight of a 55-galon drum aquarium would eventually bust in the floor boards. However, it seems reasonable that a 40 gallon tank with the dimensions of 36" x 18" x 16" should be fine since it's a pretty common size for people to keep.

Is this size cruel to the fish? Would a tank with a depth of less than 36" be cruel to the fish - like, would they be crowded? Could I just put some sort of cover over it to prevent them from hopping out?

Do you think it would be possible to keep 6 tilapia (1:5) in a 40 gallon tank? Would things work out naturally, or do I need to setup some kind of breeding tank? Would it be better to start out with just 1 male and 3 females?