Psychophysical experiments demonstrated that the hearing abilities of two damselfish species change during ontogeny. Auditory thresholds of four size-groups of juvenile bicolor damselfish. Pomacentrus partitus, and for comparative purposes, three different sized juveniles belonging to a closely related species, P. variablis, were determined through classical conditioning experiments conducted in a standing wave tube. Young juveniles (10–27 days post-metamorphosis) exhibited poor hearing, with detection limens ranging from 54 dB (at 300 Hz) to 15 dB (at 1500 Hz) higher than known adult thresholds. Thresholds decreased exponentially with increasing age, while rapidly approaching adult levels. Youngest juveniles exhibited flat, untuned audiograms, with the appearance of a best frequency and a pattern of increasing acuity progressing in a manner similar to that observed in mammals and birds.