By Maria Luisa da Silva
K. S. Boyle, G. Bolen & E. Parmentier, 2015, Journal of Zoology, 296: 249-260.
I was glad to read this article about sound production in fish, because it is a field that must be better studied and this study represents an effort to cover the lack of information. The difficulties to study behaviour in fish start because they live in the water and we are terrestrial, so this team of researchers from University of Liège, Belgium, kept some individuals of Malapterurus beninensis in several aquaria and recorded their agonistic sounds. Many fish species produce sounds and sometimes it is a mystery which structure is responsible for the sound emission. The movement of the protactor muscle linked at “elastic spring apparatus” (ESA) during the production of low frequency drumming sounds in doradid catfish has already been described, and the authors present a detailed sound analysis of broadband clicks trains, unusual emissions among catfish families, with high-quality spectrograms and oscillograms.
The sounds that the authors observed M. beninensis to make were ratchet, click train and mouth sounds. Mouth sounds were single event, of low frequency and coincided with a bite-like motion, whereas ratchet and click sounds were high-frequency and occured in trains. This species also produced bubble sounds, however they did not coincide with behavioural interactions and seemed to be by-products of air released from the orobranchial chamber or the swim bladder. The authors also show impressive images of the swim bladder obtained by computerized tomography and histological and ultrastructure analysis. What is particularly interesting is that this structure has evolved several times among Siluriformes, especially in a group that also uses electrical signals for defence. However, the scope for answering questions like the authors proposed – ‘What is the evolutionary function of the ESA morphology in Malapteruridae?’ – it is limited in laboratory experiments to analyse and to interpret natural behaviour associated with sound production. If it is possible to study this species in a semi-captive, almost natural condition, with some control and maybe with waterproof cameras to identify which individual produce the sound, we might be better able to answer evolutionary questions about sound production in these fish.