Abstract: A tank system and a method for accommodating aquatic life and particularly fish. The tank system comprises a holding tank for holding fluid to sustain aquatic life disposed therein and a filtering means in the form of a biofilter for receiving extraneous fluid from the top of the holding tank at one side thereof separated from the biofilter by a partition. A tank discharge means comprising a longitudinally extending lip surmounts the partition to permit the discharge and passage of extraneous fluid from the top of the holding tank via a prefilter to a filtering area in which the biofilter is disposed. Recirculating means including a network of pipes is provided for recirculating the extraneous fluid passed through biofilter by gravity, from the bottom of the filtering area back to the holding tank via one or pumps and a pair of water inlet lines.