The present application relates to duct stringer. The duct stringer forms at least part of a duct with a closed cross-section which is adapted to transport fluid. The duct stringer has a duct wall anda female bayonet fitting in the duct wall. The female bayonet fitting is configured to engage with a male bayonet fitting on a fluid transporting conduit to connect the fluid transporting conduit with the duct. The present application also relates to an aircraft assembly comprising the duct stringer and the fluid transporting conduit.