Triglid fish produce typical swimbladder sounds and have been mentioned in the literature as very active sound producers. Sound production and associated behaviour of the grey gurnard has been studied. The detailed physical structure of sounds produced by different size class of fish is reported. Acoustic signals of medium grey gurnard (approximately from 15 to 20 cm in total length) consist of knocks and grunts and are mainly associated with aggressive behaviour. Knocks are usually composed of 1-5 pulses, and grunts are composed of 5-40 pulses. Grunts are longer and more variable than knocks. Predominant frequencies extend up to 1700 Hz. The frequency and time structure of sounds produced by small gurnards (10 to 15 cm total length) has been compared to those of medium-sized gurnards. Seasonal and diurnal rhythms of sound production have been investigated. Sexual and developmental changes in the sound producing apparatus, the swimbladder and the sonic muscles, have been examined, to explain ontogenetic, sexual and seasonal variations in sound production in this species.