Avoidance behavior of grass carp (Ctenopharyngodon idella) shoals to low-frequency sound stimulation

Acoustic deterrence has been proven instrumental in preventing fish invasions and safeguarding against fish ingress into hydro-turbines, with the systems often employing broadband sounds, such as boat noises or predator vocalizations. However, within these broadband sounds, the specific frequencies that elicit negative phonotaxis (avoidance behavior) in fish remain to be identified. The present study investigated the avoidance behavior of grass carp shoal in sound playback experiments conducted using pure tones within the frequency range of 100–1500 Hz and two broadband sounds. The alligator roar sounds, a known deterrent, were used as broadband sound 1, which was also manipulated to remove high-sound-pressure-level components, creating a novel broadband sound 2. Grass carp exhibited significant overt avoidance behavior and increased swimming speed in response to the 100 Hz pure tone. Under the effect of this tone, the number of avoidance responses over a 10-min experimental duration (8.14 ± 1.44 min) was significantly higher than that recorded in the control group (H = 34.929, P < 0.05). These findings suggested that the low-frequency components in broadband sounds are essential to eliciting avoidance behaviors in fish. The present research offers novel insights into the strategic selection of sound frequencies in acoustic deterrence systems, facilitating the development of further precisely targeted and effective fish management strategies.