It is described a method for assembly of a fish cage (1). The fish cage (1) comprises a bottom unit (2) having a buoyancy exceeding a weight of the bottom unit (2). The bottom unit (2) comprises a body (20) configured impermeable to water. The fish cage (1) further comprises at least one wall element (30a-d, 31a-d) configured impermeable to water. The method comprises providing the bottom unit (2) on a surface (40) of a water body (4). The method further comprises connecting the at least one wall element (30a-d, 31a-d) to the body (20), thereby defining a spacing (5) impermeably separated from the water body (4).
