Summary
This paper is concerned with sound production of Doradides and Auchenopterides (Siluriformes, Pisces). Field observations (hydrofone recordings) near Manaus, Amazonas and electrophysiological investigations in INPA, Manaus have been made. 1. The drumming apparatus of the Doradides Doras, Megalodoras (Bacu) and Oxydoras (Cuiú-Cuiú) consists of the ramus Mülleri (the elastic spring of the so-called "Springfederapparat), the drumming muscles and the exomembrane. A special quality of the drumming apparatus of these genera is the fact that the elastic spring and the exomembrane are firmly connected by a strong ligament. Thus they build up a compound oscillating system. 2. Acanthodoras (Rabeca) and Trachycorystes (Kangati) have no such ligaments between the elastic spring and the exomembrane. 3. The dramming sounds of Doras and Oxydoras show a pulse repetition rate of 60-90 Hz. This rate corresponds to the frequency of the myogram responses of the dramming muscles during the stimulus-induced grunts. A drumming sound generally lasts about 40-70 msec. 4. The drumming sounds of Acanthodoras (Rabeca) show a fundamental frequency which may range over 250 Hz. In the electrophysiological experiments the frequency of myograms did not exceed 170 Hz during stimulus-induced grunts. The duration of the grunts produced under hand-held-conditions corresponds very well to the duration of the stimulus-induced grunts (100-200 msec). 5. The dramming sounds of Trachycorystes (Kangati) show a fundamental frequency of about 120 Hz. They may last several seconds.