Yik Yaw Neo

Behavioral changes in response to sound exposure and no spatial avoidance of noisy conditions in captive zebrafish.

Auditory sensitivity in fish serves various important functions, but also makes fish susceptible to noise pollution. Human-generated sounds may affect behavioral patterns of fish, both in natural conditions and in captivity. Fish are often kept for consumption in aquaculture, on display in zoos and hobby aquaria, and for medical sciences in research facilities, but little is known about the impact of ambient sounds in fish tanks. In this study, we conducted two indoor exposure experiments with zebrafish (Danio rerio). The first experiment demonstrated that exposure to moderate sound levels (112 dB re 1 μPa) can affect the swimming behavior of fish by changing group cohesion, swimming speed and swimming height. Effects were brief for both continuous and intermittent noise treatments. In the second experiment, fish could influence exposure to higher sound levels by swimming freely between an artificially noisy fish tank (120–140 dB re 1 μPa) and another with ambient noise levels (89 dB re 1 μPa). Despite initial startle responses, and a brief period in which many individuals in the noisy tank dived down to the bottom, there was no spatial avoidance or noise-dependent tank preference at all. The frequent exchange rate of about 60 fish passages per hour between tanks was not affected by continuous or intermittent exposures. In conclusion, small groups of captive zebrafish were able to detect sounds already at relatively low sound levels and adjust their behavior to it. Relatively high sound levels were at least at the on-set disturbing, but did not lead to spatial avoidance. Further research is needed to show whether zebrafish are not able to avoid noisy areas or just not bothered. Quantitatively, these data are not directly applicable to other fish species or other fish tanks, but they do indicate that sound exposure may affect fish behavior in any captive condition.

The effect of temporal variation in sound exposure on swimming and foraging behaviour of captive zebrafish

Anthropogenic noise of variable temporal patterns is increasing in both marine and freshwater systems. Aquatic animals often rely on sounds for communication and orientation, which may therefore become more difficult. Predator–prey interactions may be affected by masking of auditory cues, sound-related disturbance or attentional interference. Here, we investigated the impact on both predator and prey for zebrafish, Danio rerio, preying on water fleas, Daphnia magna. We experimentally raised ambient sound levels in an aquarium and tested four sound conditions that varied in temporal pattern: continuous, fast and slow regular intermittent and irregular intermittent, which we compared with ambient sound levels with no extra exposure. We found no effects on water flea swimming speed or depth but there was an increasing number of individual zebrafish with an increased number of startle responses, especially to the intermittent sound treatments, which was also reflected in a significant increase in zebrafish swimming speed, but not in any change in zebrafish swimming depth. Discrimination in attacking edible water fleas or inedible duckweed particles was low for the zebrafish and unaffected by sound exposure, but foraging was affected in two ways: intermittent sounds delayed the initial acceleration response and all treatments caused a rise in handling error. These insights confirm that elevated sound levels, and especially intermittent conditions, may affect predator–prey interactions. Our results apply to laboratory conditions but call for outdoor studies that go beyond single-species effects. If acoustic impact of human activities extends to multiple species and their interactions, natural sound conditions may turn out to be important for the stability and dynamics of aquatic ecosystems.

Impulsive sounds change European seabass swimming patterns: Influence of pulse repetition interval

Seismic shootings and offshore pile-driving are regularly performed, emitting significant amounts of noise that may negatively affect fish behaviour. The pulse repetition interval (PRI) of these impulsive sounds may vary considerably and influence the behavioural impact and recovery. Here, we tested the effect of four PRIs (0.5-4.0s) on European seabass swimming patterns in an outdoor basin. At the onset of the sound exposures, the fish swam faster and dived deeper in tighter shoals. PRI affected the immediate and delayed behavioural changes but not the recovery time. Our study highlights that (1) the behavioural changes of captive European seabass were consistent with previous indoor and outdoor studies; (2) PRI could influence behavioural impact differentially, which may have management implications; (3) some acoustic metrics, e.g. SELcum, may have limited predictive power to assess the strength of behavioural impacts of noise. Noise impact assessments need to consider the contribution of sound temporal structure.

Noise impact on European sea bass behavior : Temporal structure matters

Anthropogenic sounds come in different forms, varying not only in amplitude and frequency spectrum but also in temporal structure. Although fish are sensitive to the temporal characteristics of sound, little is known about how their behavior is affected by anthropogenic sounds of different temporal patterns. We investigated this question using groups of Dicentrarchus labrax (European sea bass) in an outdoor basin. Our data revealed that the temporal pattern of sound exposure is important in noise impact assessments.

Impact of Anthropogenic Noise on Aquatic Animals: From Single Species to Community-Level Effects

Anthropogenic noise underwater is on the rise and may affect aquatic animals of marine and freshwater ecosystems. Many recent studies concern some sort of impact assessment of a single species. Few studies addressed the noise impact on species interactions underwater, whereas there are some studies that address community-level impact but only on land in air. Key processes such as predator-prey or competitor interactions may be affected by the masking of auditory cues, noise-related disturbance, or attentional interference. Noise-associated changes in these interactions can cause shifts in species abundance and modify communities, leading to fundamental ecosystem changes. To gain further insight into the mechanism and generality of earlier findings, we investigated the impact on both a predator and a prey species in captivity, zebrafish (Danio rerio) preying on waterfleas (Daphnia magna).

Particle motion and pressure soundscape in outdoor vs indoor set-up

Underwater sound consists of particle motion and sound pressure. Due to technical difficulties only sound pressure is measured in most sound impact studies on fish and invertebrates. However, sound pressure alone may not adequately reflect the actual acoustic stimulus, especially in tanks, basins and near-field conditions. To test the acoustic validity of different experimental settings, we measured particle motion (in velocity) and sound pressure soundscapes of two set-ups for sound impact studies on fish: an outdoor floating pen and an indoor basin. During sound exposure, there was a gradient in particle velocity as well as in the outdoor floating pen and a standing wave in the basin. The ratio between particle velocity and sound pressure was consistent in the floating pen, but not in the basin. These findings confirm the concerns about the acoustic validity and variability between particle motion and sound pressure in basins (and tanks). Therefore, we encourage researchers to measure both particle motion and sound pressure to gain insight in the actual acoustic stimulus, in order to better interpret and understand its effect on fish and aquatic invertebrates.