To provide a closed circulation filtration aquaculture system capable of feeding sufficient oxygen gas required for nitrification in a biological filtration device. A closed circulation filtration aquaculture system in which a breeding tank for breeding fish and shellfish and a biological filtration device for biologically filtering breeding water discharged from the breeding tank are provided on a circulation channel equipped with a circulation pump and provided to circulate breeding water wherein a gas-liquid mixed water generation device for mixing oxygen gas in the form of nanolevel bubbles into the breeding water and thereby generating a gas-liquid mixed water is provided on a portion of the circulation channel positioned downstream of the breeding tank and upstream of the biological filtration device, oxygen gas is caused to be dissolved in a supersaturated state in the gas-liquid mixed water generated in the gas-liquid mixed water generation device and fed to the biological filtration device, and oxygen gas is also caused to be dissolved in a supersaturated state in the gas-liquid mixed water fed to the breeding tank after being biologically filtered in the biological filtration device.
