An aquarium includes a semi-cylindrical transparent casing for holding water and water animals and plants and covered with a top cover, a base member attached to the bottom side of the transparent casing and defining an open space, a battery-operated LED lamp detachably mounted in the open space of the base member and controllable to emit light upwardly toward the inside of the transparent casing. The battery-operated LED lamp can be removed from the base member, and attached to the top cover to emit light downwardly toward the inside of the transparent casing, or separately used as a mobile lighting tool.
