An aquarium system for aquatic organisms, comprising: an aquarium; a partition wall attached at a rear portion of the aquarium and arranged vertically to divide an inside of the aquarium into a nurturing zone constituted by a front side region in the aquarium and a purifying zone constituted by a rear side region in the aquarium; a circulation pump arranged to circulate water between the nurturing zone and the purifying zone; and at least one purifying device selected from a filter for filtering water by making the water pass through a filtering material, a protein skimmer for removing proteins contained in the water by making the proteins adhere to air bubbles, and an ultraviolet light irradiator for sterilizing the water by irradiating ultraviolet light to the water, wherein the circulation pump and the at least one purifying device constitute a unit member, wherein the unit member is mounted on a mounting frame to thereby form a purification unit, wherein the purification unit is accommodated in the purifying zone in a removably inserted manner in a state in which the unit member is mounted on the mounting frame, wherein the mounting frame is constituted by a box-shaped casing sized to be accommodated in the purifying zone in a fitted manner and configured to accommodate the unit member in a removably inserted manner, wherein the casing comprises a pump chamber in which the circulation pump is disposed, and wherein an opening portion corresponding to the pump chamber is formed on each of front and rear walls of the casing for inserting and removing the circulation pump so that the circulation pump can be removed from the purification unit after removing the purification unit from the aquarium to efficiently and assuredly perform the maintenance of the circulation pump. an aquarium; a partition wall attached at a rear portion of the aquarium and arranged vertically to divide an inside of the aquarium into a nurturing zone constituted by a front side region in the aquarium and a purifying zone constituted by a rear side region in the aquarium; a circulation pump arranged to circulate water between the nurturing zone and the purifying zone; and at least one purifying device selected from a filter for filtering water by making the water pass through a filtering material, a protein skimmer for removing proteins contained in the water by making the proteins adhere to air bubbles, and an ultraviolet light irradiator for sterilizing the water by irradiating ultraviolet light to the water, wherein the circulation pump and the at least one purifying device constitute a unit member, wherein the unit member is mounted on a mounting frame to thereby form a purification unit, wherein the purification unit is accommodated in the purifying zone in a removably inserted manner in a state in which the unit member is mounted on the mounting frame, wherein the mounting frame is constituted by a box-shaped casing sized to be accommodated in the purifying zone in a fitted manner and configured to accommodate the unit member in a removably inserted manner, wherein the casing comprises a pump chamber in which the circulation pump is disposed, and wherein an opening portion corresponding to the pump chamber is formed on each of front and rear walls of the casing for inserting and removing the circulation pump so that the circulation pump can be removed from the purification unit after removing the purification unit from the aquarium to efficiently and assuredly perform the maintenance of the circulation pump.