Underwater noise exposure induces auditory threshold shifts and metabolomic alterations in the inner ear endolymph of European sea bass.

Anthropogenic underwater noise is a pervasive pollutant in marine and aquaculture environments. However, its physiological and biochemical impacts on fish auditory systems remain poorly understood, particularly in species of ecological and aquaculture importance such as the European sea bass (Dicentrarchus labrax). Here, we combined auditory evoked potentials (AEPs) with untargeted metabolomics of inner ear endolymph to quantify noise-induced auditory threshold shifts and to identify molecular pathways affected by broadband noise exposure. A total of 114 sea bass were first assessed for baseline hearing sensitivity (100-600 Hz) and subsequently exposed to vessel-derived broadband noise concentrated below 1 kHz under two playback treatments: Medium-intensity exposure (SELcum 163-165 dB re 1 μPa2s, 30 min) and High-intensity exposure (SELcum 180 dB re 1 μPa2s, 60 min), with matched unexposed controls. Fish exposed to the High-intensity treatment showed auditory threshold shifts of 11-17 dB across all tested frequencies. Untargeted metabolomic profiling identified 752 metabolites, providing a comprehensive characterization of teleost endolymph metabolism. Noise exposure affected 199 metabolites, spanning lipids, amino acids, nucleotides, and peptides. Lipid-related subpathways, particularly sphingomyelins, plasmalogens, and long-chain acylcarnitines, were selectively enriched and formed a highly interconnected metabolic module. Notably, metabolic alterations were detected even in fish without pronounced hearing loss, indicating early inner ear responses to acoustic pollution. These results suggest that current assessments based solely on auditory thresholds may underestimate biological responses to noise exposure, highlighting the need for further investigation in marine and aquaculture contexts.