Effect of noise on the behaviour and microbiome of a common temperate estuarine fish

Underwater noise pollution is an increasing stressor in marine and estuarine environments, with anthropogenic activity altering natural soundscapes and adversely affecting animal behaviour, which is often an early indicator of environmental stress with broader physiological implications. Host-associated microbiomes, particularly the gut, are central to organism health, influencing digestion, immunity, metabolism, and stress regulation. The gut microbiome also plays a key role in linking environmental disturbances with physiological condition and behavioural changes, yet the impacts of noise on these microbial communities remain poorly understood. We examined the behavioural and gut microbial response of Pelates sexlineatus exposed to three acoustic treatments: continuous white noise (i.e. urban hum), short-pulsed white noise (i.e. intermittent boat noise), and ambient control (no added noise), under controlled aquarium conditions. Fish in ambient tanks spent the most time swimming, while fish exposed to noise exhibited increased resting and erratic movements. Microbial communities in fish and water samples, characterised using 16S rRNA gene amplicon sequencing, identified 44 phyla in the fish microbiome and 11 comprised the core microbiome. Strong differentiation was observed between fish and water communities with fish dominated by Firmicutes, Proteobacteria and Actinobacteriota, and water dominated by Bacteroidota and Proteobacteria. Although short-term acoustic exposure did not significantly alter overall microbial diversity, subtle compositional shifts and strong host-environment distinctions highlight the complexity of microbiome responses to environmental stress. This study provides novel insights into the short-term stability of the gut microbiome in estuarine fish and highlights the need for integrated research assessing behavioural and microbial responses to noise pollution.