Pulse Frequency and Water Velocity Determine Crossing Probability in Pulsed Direct-Current Fish Barriers

Abstract

Fish barrier technology by pulsed direct current has broad application potential to guide fish to suitable waters. The primary objective of this investigation was to study the effects of electric pulse frequency and water velocity on fish deterrence by pulsed direct current. The test fish were adults of two common carp species, Hypophthalmichthys nobilis (bighead carp, standard length 0.460–0.545 m) and Cyprinus carpio (Eurasian carp, standard length 0.292–0.335 m). Experiments were conducted in the 20 m swimming chamber of a 50 m flume, with a pulsed electric barrier produced by vertical electrodes located in the middle of the swimming chamber. The effectiveness of the electric barrier in deterring fish from swimming upstream past the electrodes was tested. The electric pulse generator produces a square wave pulse, with a voltage of 150 V and width of 2 ms. There were four electric pulse frequency treatments (4 Hz, 6 Hz, 8 Hz, 10 Hz), and two water velocity treatments (0.2 m/s, 0.6 m/s), with 10 replicates of each treatment. There were four primary findings. (1) Of the 160 fish tested, no fish was stunned and only 4 trembled (lost the ability to swim) for more than 2 s after encountering the electric barrier. (2) At a given water velocity, the crossing probability decreased as pulse frequency increased, and the decrease was largest when the frequency increased from 8 to 10 Hz. (3) At a given electric pulse frequency, the crossing probability was higher at the high water velocity, and barrier efficiency was more sensitive to velocity at higher pulse frequencies. (4) H. nobilis, a stronger swimmer, crossed more often than C. carpio. This study can provide ideas for the management of invasive species. However, the study was conducted under controlled laboratory conditions, and field experiments should be carried out before field applications.

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