An arrangement, a system and a method relating to a well boat- and service vessel (1) for transporting or storing fish or other aquatic organisms. There are provided, inter alia, a well boat- and service vessel (1) that includes a self-floating, exchangeable well unit (2), a propulsion unit (3), wherein the propulsion unit includes propulsion elements (4), steering and positioning elements, a dock (5) for the well unit, positioning and attachment elements for positioning and securing the well unit (2) in the dock (5).
