Abstract: An immaterial fish fence is based on a combination of low frequency mechanical vibrations and synchronously modulated electric fields, where fish approaching the fence will be given at the same time fear reactions and directional information by mechanical vibrations, and in addition will feel pain due to the electric field. The fish will then turn and swim away. The fence is implemented by means of columns positioned side by side, each comprising a number of low frequency transducers suspended above each other, each column being suspended in a float. Each column also has two electrical conductors to which a high voltage can be delivered. Thus, synchronized fields of both acoustic and electric type can be generated between and around the columns.