sound production

Fish swimbladders can serve as sound-producing organs and accessory auditory organs that transfer vibrations to the ears. Since the 1960s swimbladders have been modelled acoustically as underwater bubbles, resonant monopoles that radiate sound omni-directionally. Data inconsistent with this paradigm are typically dismissed as the result of damping by surrounding fish tissues. Fish sonic swimbladder muscles are among the fastest in vertebrates, which should be unnecessary to excite a resonant structure. Recent work however indicates that toadfish, weakfish and black drum produce sounds as a forced response whose frequency is determined by muscle contraction and not the resonant frequency of the bladder. Furthermore, the natural frequency of toadfish sounds does not vary inversely with fish size, and damping is equivalent to that of an automobile shock absorber, a device designed to suppress resonance. Toadfish produce a directional (not omnidirectional) sound field consistent with swimbladder shape, and deflation of the bladder does not change auditory thresholds. To our surprise, we recently discovered that carapid fish utilize slow muscles to produce sounds. Their swimbladder has an elastic fenestra covered by a bony plate that we believe drives the swimbladder following muscle contraction. We suggest that related ophidiid fishes, one of the commonest groups in the deep-sea bottom also have slow muscles because some species have a fenestra and muscles that occur in antagonistic pairs. Paradoxically, the striped cusk-eel produces the highest peak frequency known for swimbladder sounds, likely with a slow muscle. Fish swimbladder walls are anisotropic structures with a high water content composed of collagen. They are likely responsible for rapid damping of swimbladder sounds, and we suggest that sounds produced by slow muscles utilize additional mechanisms to drive high frequency vibrations from a structure that would otherwise damp rapidly.

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.

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.

Little information exists about how noise exposure may modulate agonistic behaviour of some sonic fish in which perception of sounds produced by conspecifics is crucial in interpreting the message conveyed by the opponents. Recently, it has been demonstrated that temporary hearing impairment can be induced by exposing fish to certain periods of white noise. Experiments were designed to test the hypothesis that elevation of hearing thresholds my means of exposure to noise) of a sonic fish, the croaking gourami Trichopsis vittata, could alter the quality of sound produced because of the altered feedback route in sound perception and production loop. This experiment also tested the hypothesis that altered characteristics of the sound produced would subsequently modulate the outcome of the behavioural contest. Test subjects were exposed to 300 - 4000 Hz white noise (142 dB; re: 1 mPa) for 12 and 24 hours, respectively. The hearing threshold shifts were evaluated at the end of noise exposure as well as one day and five days after exposure with the use of the auditory brainstem response recording protocol. The frequency range tested (600 - 2500 Hz) corresponded to the fish best hearing range as well as to the range of the croaking sounds emitted by the fish. Hearing threshold was found significantly elevated after noise exposure. Recovery, however, appeared faster in 12-hr noise exposed fish than those from the 24-hr exposure group. The croaking sounds produced by noise-exposed fish were also recorded through staged contests. The results were used to compare with the sounds produced prior to the exposure. Details of differences in sound spectra as well as changes of agonistic behaviour are presented and discussed (supported by National Organization for Hearing Research, NIMH-58198, Institute of Museum and Library Service-LL90187).

Vocalisation has been recognised as one of the important modes of animal communication. In one anabantoid fish, the croaking gourami Trichopsis vittata, both sexes produce loud, croaking sounds during agonistic encounters and courtship. It is known that sound emission of this fish is mostly involved with the ritualised portion of the contest, which is likely to convey information between the opponents about their respective strength and status. The sound is produced by a complex mechanism that involves two modified tendons, located behind each pectoral fin. Due to the external position of these soft structures, parasites, sickness, or injury from fights can easily damage the tendons, leading to muteness. Reduction or even loss of the croaking ability may result in a substantial decreasing of the overall fitness. Experiments were designed to test whether or not croaking gouramis can repair damaged tendons and regain fully functional sound producing organs, as well as to evaluate the effect of muting and recovery on the outcomes of agonistic interactions. Fishes were muted by surgically cutting one or both the tendons that connect the "sonic'' muscle with the fin rays. The occurrence and timing of recovery was evaluated for 30 specimens of T. vittata after surgical muting. Croaking sounds produced by the fish were recorded during staged contests after recovery. Sound from each specimen was previously recorded before and after muting as well, for comparison. The elapsed time of reconnection of each tendon to the relative fin ray was also recorded. Some fishes were found to recover completely within less than 30 days, while others needed up to three months. However, evidence for the beginning of the recovery process was noticed as early as 4 days after operation. Behavioural performance after recovery was normal. Details of sounds produced and changes of behavioural repertoires are discussed (supported by National Organization for Hearing Research, NIMH-58198, Institute of Museum and Library Service-LL90187).

Food begging calls are highly stereotyped innate vocalisations whose structure is very similar in quite different species. It usually consists of a series of homologous harmonic pulses. To understand species-specificity and relationship to the adult sounds, using Canary ,software we recorded and processed food begging calls from five different species of African Poicephalus parrots pertaining to two different superspecies (P.  gulielmi, supersp. robustus), and P.  senegalus, P. meyeri, P. rufiventris, P. cryptoxanthus, supersp. meyeri) from birth to 60 days of age. As the food begging call is an innate vocalisation type, it also qualifies as a useful taxonomic character. In fact, it is evolutionarily slow to change, apparently because it is unlikely to be affected by those external pressures that more quickly shape morphological characters. The general principle is that in all Poicephalus species studied, the call is structured in a series of harmonic pulses. These increase in number in the first four weeks of age, then decrease. However, at all times, a clear-cut difference among all the species is maintained up to the tenth week of age, when the differences disappear and the pulse number is two for all species. For all species studied, the main specific character appears to be the utterance rate, that is the pause duration between the different pulses. By applying a correlator analysis routine to the different species' spectrograms and subsequently a multidimensional scaling to correlation values, it clearly appears that all species' parameters segregate neatly. Within the superspecies meyeri, it also appears that P. meyeri and P. senegalus are phylogenetically the most apart, bioacoustically confirming recent molecular results.

Sciaena umbra (Linneaus, 1758) is one of the four species of Sciaenidae that are present in the Mediterranean Sea. It lives in rocky reefs or in Posidonia grass meadows; it is a nocturnal predator, sexes are separated and eggs are buoyant. It has been known to produce sounds since 1947 at least, when Dijkgraaf described sounds of Sciaena umbra observed in the Zoological Station A. Dohrn of Naples. In the UNEP Asp-protocol of 1995 it was included in the list of species whose fishery needs regulating. In the Miramare Marine Reserve (north-eastern Adriatic Sea, Trieste, Italy), S. umbra is very abundant from May to September along the artificial rocky reefs under the pier of Miramare castle. Sounds were recorded digitally at 44.1 kHz sampling rate with a Reson TC 4032 hydrophone from the pier. Recording 10 minutes each hour for a whole day (24h) confirmed that sounds are present only from late afternoon until 1 a.m. Therefore all subsequent recordings of 10 minutes each hour were carried out from 19.00 to 24.00 only. Sounds are repetitive knocks composed of 1-11 pulses, more or less regularly spaced (131.6ms ± 33.8 SD), with the main frequency components within each pulse ranging between ca. 100 and 1,200 Hz. Based on time interval between sounds, there are at least three different acoustic patterns, named irregular, regular and chorus. Sounds are emitted from May till September with irregular patterns usually followed by regular ones during a daily session. Chorus patterns were recorded only in June and July and not consistently. If S. umbra is a serial spawner like most other Sciaenidae, chorus pattern might indicate spawning bouts.

Voiced cries are described as cries where the fundamental frequency is well evident in the spectrogram, while voiceless and partially voiced cries partially or totally lack a well defined contour (Lieberman 1985: In Infant crying: Theoretical and research perspectives. (B. M. Lester & C. F. Z. Boukydis, eds.) Plenum Press; New York pp. 29-58). Some authors suggest that a greater percentage of the latter is pathognomonic of CNS damage, as happens in kernicterus due to hyperbilirubinemia (Koivisto 1987: Acta Paediatrica Scandinavia Suppl. 335, 1-73). In a study of the ontogeny of premature infant cries carried in our laboratory, we found a greater amount of voiceless and partially voiced cries in premature infants aged 34 and 40 weeks than in normal control. However, normal infants show a considerable amount of voiceless and partially voiced cries (Lenti Boero et al. 1998, Perceptual & Motor Skills 86, 1123-1140), while infants affected by severe pathologies such as congenital hypothyroidism (Lenti Boero et al. 2000: J. Child Neurology 15, 603-608) and CNS lesions induced by neonatal asphyxia, emit a lesser amount of voiceless and partially voiced cries than normal controls. In this presentation we examine this issue, both from a physioacoustic and an evolutionary perspective and suggest that disphonation might be due to different causes and that in normal infants it might have had an important evolutionary role in calling the attention of a distant care-giver.

Sound production has been widely described for territory holding fish, including cichlids, during reproductive and agonistic activities. Males of the African mouth-brooding cichlid Oreochromis mossambicus defend territories where they dig pits to attract females. Sound emissions, a series of pulses, were studied in this species to determine their association with agonistic and courtship acts. Focal observations on visual and acoustic behaviour were carried out for 8 territorial males of various sizes belonging to 5 mixed sex groups. The number of times each behavioural act occurred with and without sound emission was scored and tested for dependence. Agonistic and courtship episodes were also quantified and correlated with sound production rate. Courtship episodes were categorised into low (either 'tilt' or 'lead' occur) and high (either 'tail wagging' or 'quivering' occur) rank episodes. Sound production was significantly associated with the courtship acts 'tail wagging' and 'quivering' in all fish and with 'pit circling' and 'dig' in larger males. Courtship episodes were positively correlated with sound emission rate, though only for high rank episodes in small individuals. Sound production was not significantly associated with agonistic behaviour.

We examined the relationship between the spectral quality of the acoustic environment, the courtship sounds and hearing ability of two freshwater gobies, Padogobius martensii and P. nigricans. Sounds of P. nigricans were more intense and had a narrower frequency range than those of P. martensii, yet sound energy peaked at around 100 Hz in both species. Audiograms, obtained with evoked potentials, exhibited thresholds and bandwidth characteristics typical of hearing generalists. Maximum sensitivity occurred at 100 Hz, and thresholds increased sharply at higher frequencies. Hearing abilities in P. martensii were superior to those of P. nigricans in terms of threshold and bandwidth. Species difference in hearing correlated with differences in the amplitude and spectral content of their sounds. Underwater recordings revealed the presence of lowest noise levels at frequencies around 100 Hz, where sound energy in both species was maximal.