Acoustic and postural displays in a miniature and transparent teleost fish, Danionella dracula

Acoustic communication is widespread across vertebrates, including among fishes. We report robust acoustic displays during aggressive interactions for a laboratory colony of Danionella dracula, a relatively recently discovered miniature and transparent species of teleost fish closely related to zebrafish (Danio rerio). Males produce bursts of pulsatile, click-like sounds and a distinct postural display, extension of a hypertrophied lower jaw, during aggressive but not courtship interactions. Females lack a hypertrophied lower jaw and show no evidence of sound production or jaw extension in such contexts. Novel pairs of size-matched or -mismatched males were combined in resident-intruder assays where sound production and jaw extension could be linked to individuals. Resident males produce significantly more sound pulses and extend their jaw more often than intruders in both dyad contexts, and relatively larger males are significantly more sonic and exhibit more jaw extensions in size-mismatched pairs. The majority of highest sound producers in both contexts also show increased jaw extension during periods of heightened sonic activity. These studies firmly establish D. dracula as a sound-producing species that modulates both acoustic and postural displays during aggressive interactions based on either residency or body size, providing a foundation for further investigating the role of multimodal displays in a new model clade for neurogenomic studies of aggression, courtship, and other social interactions.