Abstract: A heat exchanger equipped for indirect heating, stirring and steam removal is charged with a finely divided fish mass, whereafter a combined boiling and drying procedure is carried out in the heat exchanger with essentially continuous heat supply and steam removal until the heat exchanger contains fish meal with a desired low water content and oil content. The oil removal is effected during part of the period for said boiling and drying procedure by feeding fish mass from the heat exchanger to a decanter having three separate outlets for separated sludge phase, oil phase and water phase while continuously recirculating to the heat exchanger the sludge phase separated in the decanter, removing separated oil for storing or further treatment, and removing separated stick water, at least part of the stick water being recirculated to the heat exchanger and/or being remixed with the fish mass discharged from the heat exchanger to be fed into the decanter.