Closed, spherical cage device (10) suitable for farming fish in a position floating in water, comprising a pattern of polygons divided along boundary lines, the boundary lines consisting of tubular elements (11) which together form a spherical skeleton. A plurality of panes (13) are covered by at least one layer of seine net (51, 52), netting, or the like, the tubular members (11) containing at least one inflatable buoyancy member (60) having fluid communication to a reservoir of pressurized gas. A control unit (33) is arranged to regulate the amount of gas in the buoyancy elements, the pipe elements (11) being connected at nodes (12) by means of sleeves (42) and finger brackets (40) and the pipe elements being arranged to allow inflow of water in the parts of the pipe elements (11) not occupied by the buoyancy element (60).