Toadfish croaks and grunts grow deeper and louder with age, according to a recent study.
Raquel Vasconcelos and Friedrich Ladich studied the hearing ability and calls of the Lusitanian toadfish (Halobatrachus didactylus) of different ages and reported their results in the latest issue of the Journal of Experimental Biology.
The Lusitanian toadfish is a coastal species found in the eastern Atlantic between the southern Bay of Biscay to Ghana (including the western Mediterranean).
The species is capable of a relatively complex acoustic repertoire of at least four different low-frequency vocalizations.
The authors studied the hearing and vocalization ability of the toadfish from a few months to 8 years old by recording and analyzing the calls, and then implanting electrodes in the brainstem to measure the response of individual fishes to sounds.
The researchers found that most very young fish (2.8"3.8 cm standard length) did not exhibit vocal activity, with only the heaviest fish in this group doing so.
They also found the very young fish to be insensitive to the grunts of the adult fish, and that the frequency, number and duration of grunts in the toadfish changed with age (older fish produced shorter, lower-frequency grunts that were also louder).
The authors surmise that he vocalizations produced during different developmental stages showed clear changes in temporal characteristics, spectral content and intensities. These changes are perhaps associated with the swimbladder and intrinsic sonic muscles, which both increase in size throughout life in H. didactylus.
For more information, see the paper: Vasconcelos, RO and F Ladich (2008) Development of vocalization, auditory sensitivity and acoustic communication in the Lusitanian toadfish Halobatrachus didactylus. Journal of Experimental Biology 211, pp. 502"509.