Fish farming cage utilizing live biomass as driving force for water exchange

A floating fish cage for farming of fish, the fish cage comprising:

• one of a water-tight outer wall and a close to water-tight outer wall, and the outer wall is form stable;
• an entrance for water into the fish cage;
• an outlet for water out of the fish cage at a lower portion;
• and
• buoyancy means,
• wherein the fish cage comprises at least two compartments, the at least two compartments comprise a fish compartment and at least one passage;
• the at least one passage comprises the entrance and an inlet at an upper portion;
• the fish compartment comprises the outlet and is in fluid communication with the at least one passage through the inlet;
• the fish compartment is adapted to keep a shoal of fish in a region between the inlet and the outlet, said shoal of fish comprises fish with one of the characteristics:
• negative buoyancy,
• swimming in circle, and
• negative buoyancy and swimming in circle;
• the fish compartment and the passage are circular shaped and positioned concentrically, and an inner wall between the fish compartment and the passage is connected to a bottom of the fish compartment, such that the shoal of fish creates a water flow from the entrance through the pas-sage and the fish compartment and to the outlet.