Abstract

A fish barrier to prevent passage there past of fish is established by applying alternating asymmetrical pulses across water immersed anode and cathode electrodes, where the cathode electrode represents the barrier. A higher voltage negative pulse produces a direct current field in a first zone adjacent the cathode electrode which zone is sensed by the fish at a threshold value of field intensity. The first zone induces a neuromuscular twitch response to turn the fish away from the negative electrode. A lower voltage positive pulse produces an alternating current field in a second zone closer to the cathode electrode, which zone is sensed only by those fish in close proximity to the cathode electrode. The second zone induces muscular contraction followed by tetany and usually death. By placing the cathode electrode across a stream or canal to prevent upstream fish movement, most of the fish will be involuntarily prevented from swimming close to the barrier. The dying and dead fish which did swim too close to the cathode electrode will be carried downstream and away from the barrier by the water flow. The use of alternating pulses of essentially equal energy level prevents degradation of the field intensity by preventing a build-up of metallic oxides on the cathode electrode due to electrolysis.