A net pen (2) and wires (3) attached to a floating ring (1). To the wires (3) a weight (4) is fastened and a bottom ring (6) slides along the wires (3). Floats (5) are sliding along the wires (3) and are attached to the net pen (2). An air-regulated ballast block (8) is secured to the bottom ring (6). The air-regulated ballast block (8) is designed like a tank provided with an opening (9) for air and with water intakes (11).
