Behavioural response of chub, barbel and brown trout to pulsed direct current electric fields

Electrified fish guidance and trash racks at water intakes are a promising technology to divert downstream moving fish away from turbines and towards a safe bypass route. Current recommendations on pulsed direct current (pDC) waveforms to electrify such racks are based on a limited number of field studies, and hence investigations comparing pDC waveforms are needed. To this end, systematic tests of electrosensitivity to pDC waveforms were performed with wild caught brown trout (<em>Salmo trutta</em>), chub (<em>Squalius cephalus</em>) and barbel (<em>Barbus barbus</em>) to determine (1) behaviour types and thresholds exhibited by different species and variation within species families, (2) the effect of fish body size, and (3) optimal parameters of pDC waveforms for possible use at electrified bar racks. Both the peak power density threshold triggering immobilization and twitch reactions decreased with increasing fish size according to a power law relation. Increasing frequency led to lower thresholds for immobilization and higher thresholds for twitch reactions. Though some inter-specific variation was observed, a waveform with a pulse duration of 2 ms and a frequency of 10 Hz was determined to be the most promising for all three species to be tested and possibly used at electrified bar racks.