Ontogenetic development of auditory sensitivity and sound production in the squeaker catfish Synodontis schoutedeni

Abstract

BackgroundSurveys of ontogenetic development of hearing and sound production in fish are scarce, and the ontogenetic development of acoustic communication has been investigated in only two fish species so far. Studies on the labyrinth fish Trichopsis vittata and the toadfish Halobatrachus didactylus show that the ability to detect conspecific sounds develops during growth. In otophysine fish, which are characterized by Weberian ossicles and improved hearing sensitivities, the ontogenetic development of sound communication has never been investigated. We analysed the ontogeny of the auditory sensitivity and vocalizations in the mochokid catfish Synodontis schoutedeni. Mochokid catfishes of the genus Synodontis are commonly called squeakers because they produce broadband stridulation sounds during abduction and adduction of pectoral fin spines. Fish from six different size groups - from 22 mm standard length to 126 mm - were studied. Hearing thresholds were measured between 50 Hz and 6 kHz using the auditory evoked potentials recording technique; stridulation sounds were recorded and their sound pressure levels determined. Finally, absolute sound power spectra were compared to auditory sensitivity curves within each size group.ResultsThe smallest juveniles showed the poorest hearing abilities of all size groups between 50 and 1,000 Hz and highest hearing sensitivity at 5 and 6 kHz. The duration of abduction and adduction sounds and the pulse period increased and sound pressure level (in animals smaller than 58 mm) increased, while the dominant frequency of sounds decreased with size in animals larger than 37 mm. Comparisons between audiograms and sound spectra revealed that the most sensitive frequencies correlate with the dominant frequencies of stridulation sounds in all S. schoutedeni size groups and that all specimens are able to detect sounds of all size groups.ConclusionsThis study on the squeaker catfish S. schoutedeni is the first to demonstrate that absolute hearing sensitivity changes during ontogeny in an otophysine fish. This contrasts with prior studies on two cypriniform fish species in which no such change could be observed. Furthermore, S. schoutedeni can detect conspecific sounds at all stages of development, again contrasting with prior findings in fishes.

Sound production to electric discharge: sonic muscle evolution in progress inSynodontisspp. catfishes (Mochokidae)

“…All species examined showed a broad range of sensitivity, as is known from other otophysan fishes [30][31][32][33].…”

Vocal differentiation parallels development of auditory saccular sensitivity in a highly soniferous fish

“…However, acoustic communication might be absent during early developmental stages because of poor hearing sensitivity, as in the gourami (Trichopsis vittata) (Wysocki and Ladich, 2001). Yet, at least in some species, it may occur during a wide range of developmental stages, as in the catfish (Synodontis schoutedeni) (Lechner et al, 2010). Nevertheless, these studies only focused on simple-pulsed sounds produced in distress/ agonistic contexts and they do not report any evidence of vocal differentiation that would facilitate acoustic communication in these species.…”

“…1 µPa at 0.8-3.0 kHz and a shift in the best frequency from 2.5 kHz to 1.5 kHz. Likewise, Lechner et al (2010Lechner et al ( , 2011 reported a considerable increase in auditory sensitivity and shift in the best frequency with development in two catfish species. Lechner et al (2010) reported an ontogenetic increase in Synodontis schoutedeni auditory sensitivity of 26 dB re.…”

“…The refinement in some of these signal characteristics with age is probably due to ontogenetic changes in the size and/or resonance properties of the soundgenerating apparatus (e.g. Myrberg et al, 1993;Amorim and Hawkins, 2005;Lechner et al, 2010). It remains unclear whether fish that produce more complex acoustic signals exhibit vocal differentiation, which could potentially result from ontogenetic modifications of the motor circuitry of the vocal pathways as in birds or mammals (e.g.…”

Developmental variation in sound production in water and air in the blue catfish Ictalurus furcatus

“…Blue catfish are also cannibalized by their own species (Chandler, 1998;Schloesser et al, 2011), and catfish have specialized hearing that is sensitive at low thresholds and high frequencies (Ladich, 1999;Ladich and Fay, 2013;Lechner et al, 2010;Papes and Ladich, 2011). Most fish predators that consume them would be less well tuned to the frequency spectrum of the blue catfish sounds than would bird predators (Dooling, 1982).…”