Auditory representation of conspecific calls improves throughout ontogeny in a singing fish.

A central question in understanding acoustic communication systems is how auditory processing develops relative to vocal differentiation. While the development of auditory processing of conspecific vocalizations has been studied in songbirds and mammals, it remains unexplored in fish. The Lusitanian toadfish (Halobatrachus didactylus) is an highly soniferous fish that exhibits sound production early in ontogeny, representing an ideal model to investigate the development of the vertebrate auditory-vocal system. Based on the auditory evoked potential (AEP) recording technique, we evaluated differences in auditory representation of boatwhistles (reproductive, agonistic and juvenile calls) and territorial grunts between different-sized toadfish groups-small juveniles (1.4-1.8 cm standard length), large juveniles (6.7-10.6 cm) and adults (up to 36 cm). Significant ontogenetic improvements were found in representing temporal patterns of boatwhistles (response latency and duration) and grunts (latency, pulse period and duration), as well as in detecting boatwhistle amplitude modulation. These acoustic parameters can potentially function as social cues for individual quality, motivation and mate choice. We present the first evidence of ontogenetic refinement in resolving fine features of conspecific calls in a fish species, suggesting this may be a conserved mechanism enhancing social communication across vocal vertebrates.