Differential acoustic response specificity and directionality in the round goby, Neogobius melanostomus

The ability to differentiate and localize conspecific calls from the ambient soundscape is particularly challenging for aquatic animals because of the increased wavelength, and concomitant increased distortion, of sound underwater. The increased wavelength is especially problematic for fish because of the relatively small space between their two ears, making interaural comparisons difficult. We presented round goby with conspecific calls, two heterospecific calls (Padogobius bonelli and Gobius niger), white noise and a 100 Hz tone burst to ascertain the effects of sound structure on localization abilities. The round goby has no obvious hearing specializations, causing theory to predict that it should not be able to localize sounds. In the laboratory, fish were presented with a silent speaker and a speaker playing one sound of interest and their behavioural response was quantified. In all trials except those using Gobius niger calls, fish preferentially selected the playing speaker over the silent but the intensity of this response differed with sound type. When the round goby call was played, fish came closer to the speaker and swam faster when responding. Also, the ability to directionalize the sound, measured by examining the path taken to the speaker, was significantly better when the conspecific call was played than when other sounds were presented. While it is still unclear how the round goby is able to directionalize the conspecific call, it appears clear they can directionalize, and possibly localize, conspecific calls as well as differentiate between call types.