Abstract: A method of processing fish includes inserting hollow needles (32) into fish bodies (22) to be treated. The fish bodies (22) are supported in a treatment chamber (12) and each needle (32) inserted into a fish body (22) defines a passage having a discharge opening (36) placed inside the fish body (22). The passage in a needle (32) is in flow communication with a treatment gas supply. A treatment gas is fed into the fish bodies (22) via the needles (32) inserted in the fish bodies (22). A negative pressure is maintained in the treatment chamber (12) for inducing the treatment gas fed into the fish bodies (22) to be drawn through the fish bodies (22) thereby exposing the fish bodies (22) to the treatment gas for the processing thereof.