A method to displace water from a water filled closed sea pen of a sealed sea pen fabric (12) is disclosed. It is characterized in that a grid shaped cage (40,150) is arranged down in the volume of water (100) inside the sea pen, and the water is withdrawn from the sea cage through a pipe or a hose (18) which is arranged inside of the grid cage (40,150), so that the sea pen fabric (12) is gradually brought to squeeze up against the outside of the grid cage. An arrangement to displace and remove water from a water filled closed sea pen of water tight sea pen fabric (12) as defined in the method, is also disclosed.
