Behavioural responses to sound exposure in captivity by two fish species with different hearing ability

Underwater sound generated by human activities is increasing in, on and near aquatic environments. Such anthropogenic noise can induce artificially elevated ambient sound levels and cause various detrimental effects in fish, such as temporary or permanent hearing loss, masking of relevant acoustic signals and cues or behavioural changes that may have fitness consequences. Also, captive fish are often exposed to noisy conditions, which may have consequences for production in aquaculture, biases in scientific results in laboratories or welfare in hobby aquaria. However, we still have limited insight into how fish cope with artificial sound exposure and how species differ in sensitivity. Here, we compared zebrafish, Danio rerio, and Lake Victoria cichlids, Haplochromis piceatus, the former being sensitive to lower absolute thresholds and wider spectral ranges than the latter. Experimental sound exposure induced a significant reduction in swimming speed in the first minute of exposure for both species in captive conditions. Furthermore, zebrafish showed clear startle response behaviour with the onset of the sound exposure leading to an initial, brief increase in swimming speed, which was not found for the cichlids. Neither species showed spatial shifts away from the active speaker in the horizontal plane, but cichlids shifted downwards to spend more time in the bottom area of the fish tank after the onset of sound exposure, while zebrafish retained their average swimming height during the same exposure levels. Our results show that sound exposure can cause both similar and species-specific responses in two fish species and that these responses are not obviously related to differences in their hearing ability.