Effects of Noise Exposure and Ageing on Anxiety and Social Behaviour in Zebrafish

Simple Summary As animals age, exposure to additional environmental stressors such as noise pollution might be more detrimental at the physiological and behavioural levels, but such an effect is not yet clear. In this study, we tested the effects of noise exposure for 24 h on young adults and old zebrafish. Based on different behavioural tests, we found that both noise and ageing caused anxiety responses when the animals were introduced to a novel environment as well as a tendency for social proximity. Such anxiety responses decreased when the animals were tested in groups. Since the old zebrafish already showed anxiety-like behaviour with a preference for bottom dwelling, noise treatment induced the opposite effect in these individuals, increasing their vertical exploration. This work is a first attempt to investigate the effects of noise and ageing on zebrafish, a reference model in hearing and ecotoxicology research. Overall, we suggest that old individuals may have distinct physiological and behavioural mechanisms for dealing with noisy environments.Abstract Noise pollution is creating a wide range of health problems related to physiological stress and anxiety that impact the social life of vertebrates, including humans. Ageing is known to be associated with changes in susceptibility to acoustic stimuli; however, the interaction between noise effects and senescence is not well understood. We tested the effects of 24 h continuous white noise (150 dB re 1 Pa) on both young adults and old zebrafish in terms of anxiety (novel tank diving test), social interactions (with mirror/conspecific attraction), and shoaling behaviour. Both noise and ageing induced higher anxiety responses in a novel environment. Since the old zebrafish showed longer bottom dwelling, acoustic treatment induced the opposite pattern with an initial increase in vertical exploration in the aged individuals. Both noise- and age-related anxiety responses were lowered when individuals were tested within a group. Regarding social interactions, both noise and ageing seemed to cause an increase in their proximity to a mirror. Although the results were not statistically significant, noise exposure seemed to further enhance conspecific attraction. Moreover, the interindividual distance within a shoal decreased with noise treatment in the aged individuals. This study is a first attempt to investigate the effects of both noise and ageing on zebrafish behaviour, suggesting the age-dependent physiological coping mechanisms associated with environmental stress.