fish

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).

There is growing concern that aquatic vertebrates may be affected by the increasing noise of anthropogenic origin in their environment. Several studies have been conducted on the effects of noise on marine mammals, but only a few studies have dealt with fish. The aim of the present study is to measure and compare the immediate effects of intense noise exposure (160 dB re 1 µPa for 12 and 24 hours) on two otophysine fish species, the non-vocal cyprinid Carassius auratus and the catfish Pimelodus pictus, which produces low-frequency drumming and high-pitched stridulatory-sounds. The second aim of this study was to determine the effects of noise on the ability of P. pictus to communicate acoustically. Hearing sensitivity was determined utilising the auditory evoked potential (AEP) recording technique. Measurements were performed prior and directly after noise exposure as well as after several days of recovery. Threshold shifts immediately after noise exposure ranged from 13-22 dB in C. auratus and from 7-34 dB in P. pictus. In both species the greatest hearing loss occurred at their most sensitive frequencies (C. auratus: 500 - 1000 Hz; P. pictus: 500-4000 Hz). Sound energies in the pimeloid catfish were maximally 10 dB above hearing curves immediately after noise exposure. Differences in recovery were observed between species. Carassius auratus recovered completely after 3 days, whereas in Pimelodus pictus reduced auditory sensitivity of up to 15 dB was still observed after 3 days. Our results showed that these two hearing specialists are differently affected by noise exposure and that the threshold shifts are more persistent in P. pictus. The hearing loss in the vocalising pimelodid catfish indicates that sound communication is impaired in noisy environments. This research was supported by the Austrian Science Fund (FWF No 12411 to F.L.).

Underwater noise pollution is becoming a pressing environmental issue that could affect aquatic wildlife, but very little research has been done on this topic. The effect can be even more dramatic for species actively using acoustic signals for communication and assessment of quality of opponents during agonistic encounters. We examined the effects of underwater noise on auditory sensitivity and aggressive behaviour in the vocalising skunk loach Botia morleti. Fish were exposed to white noise (142 do re: 1 µPa) for 12 hours and shifts of auditory threshold were measured with the auditory brainstem response protocol. Noise exposure resulted in elevated auditory thresholds throughout the entire auditory range. It was also found that significant recovery occurred in approximately 9 hours. The effects of noise-exposure on behaviour during aggressive contests were investigated by comparing contest dynamics between noise-exposed fish and a resident (non-exposed fish). The results showed that noise-exposure could influence behaviour in two ways: 1) contest durations with noise-exposed fish were significantly shorter; and 2) noise-exposed fish tended to engage in more re-escalation of contests than those with control fish. Two mechanisms (direct, indirect) were proposed to explain the findings. In the direct effect, noise exposure causes direct stress on the fish which results in decreased contest duration. In the indirect effect, the noise exposure cause a temporary hearing loss which results in a misperception of the acoustic signal emitted by the opponents. The sound perception and production feedback loop is compromised due to noise exposure (i.e., elevation of hearing threshold) and as a result, contests are repeatedly re-escalated because the information content of the signal can not be accurately perceived by the noise-exposed fish. The present study demonstrates that noise pollution could have dire physiological impacts as well as behavioural consequences (supported by National Organization for Hearing Research, N1MH-58198, Institute of Museum and Library Service-LL90187).

The underwater acoustic environment is inherently loud as a result of ambient sounds. In addition, there is an increasing amount of sound from anthropogenic sources, which produce noise within the hearing range of most fish (less than 1.0 kHz). For fish, the auditory system is one of the most important sensory systems because it provides information about ambient sounds, prey items, predators and potential mates. Since a fish's ability to accurately interpret its acoustic environment is essential for its survival, it is important to understand how noise affects sound perception ability of fish. This study examines the question: does noise exposure affect auditory sensitivity differently in hearing specialists (fish with coupling devices between the gasbladder or ancillary structures and inner ear, enhancing overall hearing with wider frequency range and lower threshold) and hearing generalists (fish without coupling devices, with narrow frequency range and higher threshold)? For this study, a hearing specialist species, the fathead minnow Pimephales promelas, and a hearing generalist species, the bluegill sunfish Lepomis macrochirus, were used to examine: (1) the immediate effects on auditory threshold of white noise exposure at various exposure durations (1-24 h at 0.3-4.0 kHz, 142 dB re: 1µPa); and (2) recovery time after noise exposure (1-14 days). Audiograms for noise-exposed fish were measured using the auditory brainstem response protocol, which records acoustically evoked brainwaves, and compared to control fish (no noise exposure). The results for specialists showed that their best hearing frequency range (0.8-2.0 kHz) was affected significantly more than other frequencies. In addition, recovery of hearing ability after noise exposure was found to be both frequency- and exposure-dependent. The results for hearing generalist fish will be presented and discussed (work supported by the Kentucky Academy of Science, National Organization for Hearing Research, NIMH-58198, Institute of Museum and Library Service-LL90187).

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.

Acoustic researches were made in the Miramare Marine Reserve (Gulf of Trieste, Adriatic Sea, Italy) and just outside it in order to evaluate interferences between fish acoustic communication and man-made under- water noise due to the passage of outboard engine boats. Average sea ambient noise was recorded both inside and outside the protected area because in the reserve the passage of boats is intermittent, while outside the boat traffic is intense. Then observations in tanks and in the field were made on the territorial agonistic behaviour of the red mouth goby Gobius cruentatus, a benthic fish present in and out the protected area. Two different fish sounds were recorded: a train of distinct knocks and a drumming sound, a less regular spaced train. The frequency range is from 50 Hz up to 800 Hz with highest amplitude below 200 Hz. Meanwhile the boat noise was recorded from the smaller distance between engine source and fish inside (200 metres) and outside (10 metres) the preserved area. Finally all of these recordings were compared in a frequency - P.S.D. graph. The result of the comparison suggests that in the Reserve the acoustic communication in G. cruentatus is undisturbed and that this approach is a useful method to assess and prevent the impact of man-made noise in a protected area.

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.

Many species of fish are vocal and several studies have shown that these sounds emitted by fish have a communicative function. One group of marine fish, the Gadidae or codfish, contains a large number of vocal species. Codfish calls are relatively simple and species-characteristic. However, one gadoid, the haddock, produces a range of different calls in different social contexts. Both male and female haddock produce short sequences of repeated 'knocks' during aggressive encounters. But during reproductive behaviour male fish produce calls that vary in their characteristics as courtship proceeds. We have recently re-examined the repertoire of sounds produced by a small group of spawning haddock, and have attempted to relate the sounds made by males to the different patterns of behaviour shown by the fish. We have also characterised the sequences of behavioural acts that lead up to spawning. Haddock sounds were classified into single and multiple 'knocks'. Each 'knock' was composed of two low frequency pulses. Multiple 'knocks' were further split into 5 different categories based on sound duration and 'knock' repetition rate. The behavioural acts Follow, Flaunt, Solitary Display and Lateral Display were significantly associated with sound production. Sounds became longer and showed higher 'knock' repetition rates as the male fish became more aroused and came closer to spawning. It is suggested that the sounds serve to bring male and female fish together, in the same part of the ocean, and that sounds also play a role in synchronising the reproductive behaviour of the male and female fish.