[descry]

in my earth/space science class i have to make an ecosystem in a fishtank, with living animals (ie, frogs, snails etc, living things that can survive harsh environments). has anyone here had to do this before, and even of you havnt, i need some sugestions, im retarded, all my creatures are gonna die.
oh, they are gonna be sealed away in the fishtank for 4 weeks, so i need food sources and shit like that. i need alittle help here.