Male painted gobies (Pomatoschistus pictus) vocalise to defend territories

Many fish species emit sounds in agonistic contexts. During direct confrontations sounds are typically produced during the display phase in conjunction with visual exhibitions. Here we studied sound production during territorial defence in captive painted gobies, Pomatoschistus pictus, and related acoustic parameters with male traits and the date of recording (Julian day, i.e., with the approach of the peak of the breeding season). Territorial males emitted drumming sounds during displays that involved darkening the chin and fins, spreading fins and quivering the body. Drums were trains of low frequency pulses (approximate to 23 pulses) repeated every 27 ms and usually lasting under a second. Drums were produced in short sequences of sounds (bursts). All acoustic parameters differed significantly among males. Drum and burst duration, and drum number of pulses increased significantly with male size. Calling duration (including drum, burst duration and drum number of pulses) also increased significantly with Julian date and presented a high intra-male variability, suggesting that these parameters may also depend on the individual's motivation. We provide the first report for agonistic sound production in sand gobies and give evidence that sound parameters contain information that can be used during mutual assessment in contests over territories.