Laying the foundations for selective-fish guidance using electricity: multi-species response to pulsed direct currents

To develop effective technology that employs electric fields to simultaneously guide valued freshwater fish whilst limiting the range expansion of undesirable invasive species, there is a need to quantify the electrosensitivity of multiple families. This experimental study quantified the electrosensitivity of two carp species that, in UK, are invasive (grass carp, <i>Ctenopharyngodon idella</i>, and common carp, <i>Cyprinus carpio</i>) and compared the values with those previously obtained for adult European eel (<i>Anguilla anguilla</i>), a species of conservation concern in Europe. Electric field strengths (V/cm) required to elicit physiological responses (<i>twitch</i>, <i>loss of orientation</i> and <i>tetany</i>) were identified across four pulsed direct current (PDC) electric waveforms (single pulse-2 Hz, double pulse-2 Hz, single pulse-3 Hz and double pulse-3 Hz). Grass carp were sensitive to differences in waveform with <i>tetany</i> exhibited at lower field strengths in the single pulse-2 Hz treatment. Both cyprinid species responded similarly and were less sensitive to PDC than adult European eel, although <i>loss of orientation</i> occurred at lower field strengths for grass than common carp in the single pulse-3 Hz waveform treatment. This variation in electrosensitivity, likely due to differences in body length, indicates potential for electric fields to selectively guide fish in areas where invasive and native species occur in sympatry.