The Effect of Electrical Waveform Shape on the Mortality of Steelhead Embryos and Larvae

Pacific salmonids have a worldwide distribution.  Some native salmonid populations are endangered, whereas introduced populations can harm native fish communities.  Electricity is used as a tool for the conservation and monitoring of native fishes and also for the control or removal of non-native fish.  The susceptibility of juvenile and adult fish to injury and death from electric shock can differ among waveform shapes.  However, surprisingly little is known about which waveform shape is most injurious to embryos and larvae.  To address this, we exposed the embryos and larvae of hatchery steelhead to three waveforms shapes often emitted by electrofishers:  sine alternating current (AC), pulsed square direct current (square), and pulsed ½-sine direct current (½-sine).  For each waveform, developing fish were shocked at 6 stages (blastula, gastrula, segmentation, organogenesis, alevin, and swim up) over 2-3 different voltage gradients.  Shock frequency (60 Hz), pulse width (8.33 ms), and exposure duration (30 sec) were held constant among treatments.  AC and square waveform shapes were more deadly, mortality was positively related to voltage gradient, and sensitivity varied by developmental stage.   The sensitivity of young fish to different waveform shapes should be considered when employing electric fields in both fisheries conservation and control efforts.