A sea-pen arrangement is for farming fish. The sea-pen arrangement has a service unit with a plurality of shafts projecting downwards and a pontoon at their lower portions. The shafts define an inner area. A net forms a closed enclosure. The sea-pen arrangement further includes at least one sea pen positioned in an outer area on the outside of two shafts. A frame structure has an upper frame with a first fastening portion and a second fastening portion, a bottom frame, and a fence fastened to the upper frame and the bottom frame. The frame structure is fastened to the service unit at the fastening portions, and the frame structure surrounds the at least one sea pen in the outer area.
