A buoyancy element (I) for constmcting a modular buoyancy system (2) for a circularly shaped net cage (3), the buoyancy element (I) including a cage side (I I), an opposite straight long side (13), coupling sides ( 15, 1 7) between the cage side ( 11) and the stTa ight long side (13), and the cage side (11) being curved, following the periphery of the net cage (3).