AUDITORY THRESHOLDS OF THE JUVENILE BIGHEAD CARP (ARISTICHTHYS NOBILIS) WITH DIFFERENT BODY LENGTH

The bighead carp (<italic>Aristichthys nobilis</italic>) is an economically and ecologically vital species in Asian freshwater systems. Its hearing capability, crucial for survival behaviors like predator avoidance and communication, is enhanced by the Weberian apparatus connecting the swim bladder to the inner ear. However, little is known about the ontogenetic development of auditory sensitivity, particularly during the critical juvenile stage. This study aimed to quantify the auditory thresholds of juvenile bighead carp across different body sizes to elucidate hearing development and establish a physiological basis for acoustic-based management. Using the non-invasive Auditory Evoked Potential (AEP) technique, we measured hearing in 30 juveniles divided into three size groups: small (7.9±0.4) cm, medium (10.9±0.8) cm, and large (14.2±0.7) cm. Auditory thresholds were determined for pure tone bursts (100—2000 Hz) under controlled lab conditions. The threshold was objectively defined as the lowest sound level eliciting a repeatable neural response, confirmed by analyzing AEP waveforms from phase-inverted (90° and 270°) stimuli to cancel artifacts. Results revealed an asymmetrical “V-shaped” audiogram for all groups, indicating specialized low-frequency hearing. The maximum sensitivity occurred at 400 Hz [overall mean threshold: (93.0±3.0) dB re 1 µPa], while sensitivity sharply decreased at higher frequencies [reaching (125.0±4.3) dB at 2000 Hz]. A significant negative correlation was found between auditory threshold and body length, demonstrating improved hearing sensitivity with growth. This effect was most pronounced at 400 Hz, where the large-size group was 5 dB more sensitive than the small-size group (<italic>P</italic>=0.001). Significant improvements were also observed at 100 and 1000 Hz. This enhancement is likely due to the ongoing maturation of the inner ear and the Weberian apparatus-swim bladder system. Ecologically, these findings imply that smaller juveniles are more vulnerable to acoustic masking from anthropogenic noise. Our data provide essential parameters for ecological risk assessment and for developing size-selective acoustic control technologies. We recommend noise mitigation in juvenile habitats prioritize frequencies ≤400 Hz. Future studies should integrate behavioral assays to determine response thresholds and include wild and adult populations to facilitate a comprehensive, life-cycle-based management strategy.