Acoustic deterrence has been identified as a potentially effective behavioral control method to reduce the feeding on macroalgae by Siganid fish. The hearing ability of the target fish species is a key prerequisite for selecting the appropriate sound frequency used in acoustic deterrence. The auditory capabilities of juvenile Siganus guttatus were examined through the analysis of auditory evoked potentials (AEPs) to determine their auditory frequency sensitivity and corresponding threshold. In this paper, the AEPs of 14 juvenile fish with different body lengths were studied using a TDT Auditory Physiological Workstation. It was observed that all juvenile fish exhibited discernible AEP waveforms when exposed to acoustic stimulation within the frequency range of 100–800 Hz. Additionally, the amplitudes of the AEP waveforms were found to increase in conjunction with the intensity of the acoustic stimulation. As the frequency of the sound increased, the hearing threshold of the juvenile fish did so simultaneously. In terms of low-frequency sounds, those within the range of 100–300 Hz evoked greater sensitivity, with the most sensitive frequency of hearing being 200 Hz and the average auditory threshold being 104 dB. The auditory sensitivities of individuals with different body lengths were significantly different at 200–300 Hz, at which point the auditory threshold of larger individuals (4.5−5.0 cm) was significantly lower than that of smaller individuals (4.1−4.4 cm). This suggests that larger fish have a lower auditory threshold, which is related to the development of their auditory organs. Due to the heightened sensitivity of juvenile S. guttatus to sound, their low hearing threshold, and the similarity of ambient noise, it is possible to employ acoustic deterrence in the wild to decrease the incidence of macroalgal consumption by S. guttatus, thereby mitigating the economic losses associated with important macroalgae.