Flow-through fish stunner and method of stunning fish

Fish stunner apparatus for use in saltwater flow-through fish stunning comprising, an elongate stunner tube configured so that water and fish can be pumped through the tube in a flow-through manner, at least three stunning electrodes spaced along the stunner tube configured to provide, when powered, an electric field substantially longitudinally along the stunner tube, a high power alternating voltage power supply configured to supply 0v to at least one, preferably two stunning electrodes, and further configured to supply at least one high power alternating voltage to at least one remaining stunning electrode, at least the first electrode and last electrode in the direction of flow being at 0v, whereby high power alternating voltage electric fields are provided along part or substantially all of the stunner tube.