The invention relates to a method for holding fish or other species which live in the water in a circulation system (1) comprising at least one holding tank (2), at least one biological filter (3), and optionally other water treatment units (4) for example for a supply of oxygen (5), for sterilization (6), for defoaming (7), for a mechanical filtering process (8), etc. The invention additionally relates to a circulation system. In order to reduce the energy requirement, supply air is supplied to the system by at least one supply air line (60), and exhaust air is discharged by at least one exhaust air line (59). Supply and exhaust air is conducted through a heat exchanger in which heat contained in the exhaust air is transferred to the supply air, and/or the temperature of the supply air is increased to the level of the holding basin.
