Toadfish do not have a reputation for glamour, but what they lack in visual appeal they more than make up for with their chatty personalities: croaking, grunting and moaning like a boat horn (boatwhistle), even the tiniest fry get in on the action. But communication is pointless if there is no one there to hear the message, which made Raquel Vasconcelos from the University of Saint Joseph, China, and colleagues from the Universidade de Lisboa, Portugal – Andreia Ramos, Paulo Fonseca and Clara Amorim – wonder how closely hearing development in the vociferous Lusitanian toadfish (Halobatrachus didactylus) matches the development of their vocal repertoire.
Trawling for the communicative fish in the Tagus and Mira river estuaries in Portugal, the team collected animals ranging in size from dainty fry (up to 1.7–2 cm) to fully grown adults (25–35 cm) and recorded the animals’ garrulous conversations. Then they shipped fish from the three oldest groups to the University of Washington, USA, where Vasconcelos, Peter Alderks and Joseph Sisneros played short bursts of sound to the animals and measured the sensitivity of the delicate hair cells in the fish's ear to the tones.
Analysing the fish's vocal repertoire, the team noticed that the animals produced single grunts and grunt trains when competing for food, while double croaks and long trains of grunts were associated with sitting alone in shelters, and large juveniles resorted to their distinctive boatwhistles when defending their territory. They also realised that the calls became more sophisticated as the fish grew older. And when they analysed the fish's sensitivity to sound, they noticed that the hearing of the large juveniles was three times more sensitive than that of the small juveniles, while the adults’ and large juveniles’ hearing was equally sensitive.
So the fish's hearing becomes more sensitive as their vocal repertoire expands and the team adds that learning more about the interplay between the development of the two could help us to understand how communication evolved.