An aquarium includes a bottom tank which has a pump circulate water via a first pipe and a first drainage pipe provided on top of the bottom tank to maintain water level in the bottom tank in a predetermined level, a middle tank mounted on top of the bottom tank and having a filtering box, a collecting pipe, a receiving box, a lid to cover the inlet of the collecting pipe and a funnel in communication with the lid via a conduit and a top tank having a filtering plate mounted on top of the bottom to cover the through hole and having multiple apertures, a top board to cover the top tank, an illuminating device to illuminate the top tank and a feeding device mounted on top of the top board for distributing food to fish in the top tank.