Experimentally determined effectiveness of different electric barrier arrangements on the behavioural deterrent of silver carp (Hypophthalmichthys molitrix)

Abstract

Pulsed direct current electric barrier (EB) technology has been widely used to repel invasive species, guide fish away from dangerous areas, and direct them towards favourable locations, such as bypass channels. The effectiveness of an EB is influenced by many factors, and there is no consensus concerning what are the primary and secondary effects of the factors that influence fish response to EBs. In this study, Experiment 1 was conducted to investigate primary and secondary effects. It consisted of static water tests in which four factors were varied (electrode arrangement (EA), pulse voltage (PV), pulse frequency (PF), pulse width (PW)), each taking one of three values, in three phases of electrode activation (Phase I, before activating the pulsed power supply; Phase II, during the period of electrification; Phase III, after deactivating the power supply). Since the experimental design was orthogonal, nine treatments were designed and used in each phase. Experiment 2 was to identify whether there was any difference in barrier effectiveness and fish injury at different water velocities (0 m s-1, 0.3 m s-1,and 0.5 m s-1). The result showed that times of silver carp successfully passing the barrier in Phase I were significantly greater than in Phase II or Phase III for each treatment (P < 0.05), and there were no significant differences in times of successful passage among the nine treatments in phase II (P > 0.05). The primary and secondary effects of the four factors on the blocking rate and the number of fish injuries were EA > PV > PW > PF. Barrier obstruction rate and the number of fish injuries increased as fish body length increased. There was no significant difference (P > 0.05) in blocking rate or in fish injury rate as water velocity increased. The study will provide a foundational baseline for conserving fish stocks and preventing the cross-regional spread of invasive fish species.