Acoustic repertoire and anatomical features of the flying gurnard from the Adriatic Sea

Ray-finned fish communicate by emitting acoustic signals; however, many species have not yet been investigated for their ability to produce sound. Dactylopterus volitans is a marine bottom-dwelling fish occurring throughout the Atlantic Ocean and Mediterranean Sea, including the Adriatic Sea. In this study, we explored the vocal repertoire of D. volitans by analysing sounds opportunistically acquired by an action camera during a field survey in the south Adriatic Sea (Croatia). The acoustic repertoire was composed of two distinct sound types (Grunt A and Grunt B) produced in an alternating order. Grunt A was a harmonic sound composed of two to nine pulses that lasted around 30 ms. They were produced singly or in trains (bursts), and we could differentiate short- and long-intervals between the sounds within the bursts. Grunt A was harmonic and possessed up to six harmonics, with the peak frequency of around 225 Hz. Grunt B, composed of two to four pulses and lasting around 110 ms, had overlapping peak and fundamental frequencies (~170 Hz). In addition, we recorded several sounds of juvenile D. volitans. By examining the anatomy, we provide insights into the swim bladder mechanism and other anatomical features of the skull and vertebral column. The large swim bladder was separated along the midline into two rostrocaudal chambers, and the walls of each chamber were surrounded by highly vascularized intrinsic sonic muscles. The skull of D. volitans possessed two large openings situated posteriorly; the anterior extensions from the swim bladder fitted into these openings, hence shortening the distance between the bladder and inner ear. Our study establishes D. volitans as a sonic species, paving the way for future bioacoustic surveys to provide valuable insights into its status and distribution in the Adriatic Sea.