Abstract: An aquarium includes a water tank received in a picture-frame-shaped housing suitable for either mounting on a wall or being supported on a stand. The housing includes a hidden storage space for neatly storing an air pump. A vertical sheet or partition extending between the sides of the tank divides the tank into a full-width, but relatively thin and flat, bubble conduit behind the partition for carrying air bubbles, and a habitation compartment in from of it for keeping fish. The lower edge of the partition is spaced above the bottom of the tank to form a gap or water intake, and the upper edge of the partition is spaced below the water line to form a water return. An elongated air diffuser substantially extends between the side edges of the bubble conduit near its bottom. When supplied air by the pump, the diffuser emits a wide sheet of air bubbles that rise upwardly through the bubble conduit to aerate the water.