The present invention concerns 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. According to the invention there are provided, inter alia, a well boat- and service vessel (1) that comprises a self-floating, exchangeable well unit (2), a propulsion unit (3), wherein the propulsion unit comprises propulsion means (4), steering and positioning means, a dock (5) for the well unit, positioning and attachment means for positioning and securing the well unit (2) in the dock (5).
