C. gobio is solitary, maintains territories, and defends them by threat display, seldom by biting and fighting. Threatening consists of spreading gill covers and fins darkening, lowering the head and sound production. Acoustic signals of C. gobio are built up of knocking sounds produced as single pulses (50 ms) or trains of 4-6 pulses (230 ms). Frequencies extend up to 3kHz, but most sound energy is concentrated between 50 and 500 Hz in both sound types. Calling is accompanied by a nodding movement of the head, during which the pectoral girdle and the skull are moved rapidly against each other. During emission of trains of knock sounds several contractions follow rapidly at 50 ms intervals. Each contraction causes the emission of one pulse. Calling was registered throughout the year in the laboratory at seasonal temperatures between 8° and 13° C. No difference in ability of sound production was observed between sexes.