Anthropogenic Underwater Noise Induces Anxiety-like Behavior in Zebrafish

Underwater noise pollution, driven by human activities, is an emerging environmental concern, yet its effects on fish behavior and physiology remain poorly understood. As a vertebrate model with conserved stress pathways, zebrafish (<i>Danio rerio</i>) is well-suited for investigating the mechanistic basis of such impacts. We hypothesized that daytime and nighttime noise exposure would differentially induce anxiety-like behavior and associated neuroendocrine disruptions in zebrafish, with effects varying by sex. To evaluate this hypothesis, adult zebrafish were exposed to anthropogenic noise (100-1000 Hz, 130 dB) for seven days, specifically during daytime (08:00-20:00) and nighttime (20:00-08:00) periods. Behavioral assays revealed that noise exposure delayed the first entry of females into the top zone during daytime, while both sexes exhibited prolonged bottom-dwelling and reduced exploratory behavior under nighttime noise. Physiological analyses showed elevated plasma cortisol levels in females, accompanied by up-regulated HPI-axis genes, whereas males displayed a non-significant cortisol increase. Neurotransmitter profiling indicated a sex-specific response to nighttime noise: In females, brain 5-hydroxytryptamine (5-HT) showed a non-significant increasing trend, whereas in males it was significantly elevated, while dopamine (DA) decreased in both sexes. Gene expression analysis further revealed disruptions in 5-HT and DA pathways. These findings demonstrate that underwater noise induces anxiety-like behavior in zebrafish by dysregulating endocrine and neurotransmitter systems, with nighttime noise exhibiting more pronounced effects, suggesting that chronic exposure to anthropogenic noise may impair natural behavior and stress regulation in aquatic species, particularly during nighttime periods.