Methods and systems for processing fish are provided which enable removal of the head or other portion of a fish in a particularly reliable and efficient manner. The systems include a conveyor drive motor which provides continuous movement of a conveyor device for transporting fish along a transport path and which simultaneously provides intermittent movement of a blade across the transport path to sequentially sever a portion of each fish. An intermittent drive mechanism is coupled to the conveyor drive motor and coupled to the blade to convert continuous movement produced by the conveyor drive motor to intermittent movement of the blade between a standby position and a cutting position. Related methods for severing a portion of each fish in a series of transported fish are also provided.