Publications by authors named "Friedrich Ladich"

45 Publications

Both sexes produce sounds in vocal fish species: testing the hypothesis in the pygmy gourami (labyrinth fishes).

J Exp Biol 2020 05 20;223(Pt 10). Epub 2020 May 20.

Department of Behavioural Biology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria

In vocal fish species, males possess larger sound-generating organs and signal acoustically with pronounced sex-specific differences. Sound production is known in two out of three species of croaking gouramis ( and ). The present study investigates sex-specific differences in sonic organs, vocalizing behaviour and sounds emitted in the third species, the pygmy gourami, , in order to test the hypothesis that females are able to vocalize despite their less-developed sonic organs, and despite contradictory reports. Croaking gouramis stretch and pluck two enhanced (sonic) pectoral fin tendons during alternate fin beating, resulting in a series of double-pulsed bursts, termed croaking sound. We measured the diameter of the first and second sonic tendon and showed that male tendons were twice as large as in similar-sized females. We also determined the duration of dyadic contests, visual displays, number of sounds and buttings. Sexes differ in all sound characteristics but in no behavioural variable. Male sounds consisted of twice as many bursts, a higher percentage of double-pulsed bursts and a higher burst period. Additionally, male sounds had a lower dominant frequency and a higher sound level. In summary, female pygmy gouramis possessed sonic organs and vocalized in most dyadic contests. The sexual dimorphism in sonic tendons is clearly reflected in sex-specific differences in sound characteristics, but not in agonistic behaviour, supporting the hypothesis that females are vocal.
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http://dx.doi.org/10.1242/jeb.223750DOI Listing
May 2020

Auditory chain reaction: Effects of sound pressure and particle motion on auditory structures in fishes.

PLoS One 2020 27;15(3):e0230578. Epub 2020 Mar 27.

Department Biology II, Ludwig-Maximilians-University Munich, Planegg-Martinsried, Germany.

Despite the diversity in fish auditory structures, it remains elusive how otolith morphology and swim bladder-inner ear (= otophysic) connections affect otolith motion and inner ear stimulation. A recent study visualized sound-induced otolith motion; but tank acoustics revealed a complex mixture of sound pressure and particle motion. To separate sound pressure and sound-induced particle motion, we constructed a transparent standing wave tube-like tank equipped with an inertial shaker at each end while using X-ray phase contrast imaging. Driving the shakers in phase resulted in maximised sound pressure at the tank centre, whereas particle motion was maximised when shakers were driven out of phase (180°). We studied the effects of two types of otophysic connections-i.e. the Weberian apparatus (Carassius auratus) and anterior swim bladder extensions contacting the inner ears (Etroplus canarensis)-on otolith motion when fish were subjected to a 200 Hz stimulus. Saccular otolith motion was more pronounced when the swim bladder walls oscillated under the maximised sound pressure condition. The otolith motion patterns mainly matched the orientation patterns of ciliary bundles on the sensory epithelia. Our setup enabled the characterization of the interplay between the auditory structures and provided first experimental evidence of how different types of otophysic connections affect otolith motion.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0230578PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7100961PMC
June 2020

Temperature affects sound production in fish with two sets of sonic organs: The Pictus cat.

Comp Biochem Physiol A Mol Integr Physiol 2020 02 22;240:110589. Epub 2019 Oct 22.

Department of Behavioural Biology, University of Vienna, Althanstraße 14, 1090 Wien, Austria. Electronic address:

Sound communication is affected by ambient temperature in ectothermic animals including fishes. The present study examines the effects of temperature on acoustic signaling in a fish species possessing two different sound-generating mechanisms. The Amazonian Pictus catfish Pimelodus pictus produces low-frequency harmonic sounds (swimbladder drumming muscles) and high-frequency stridulation sounds (rubbing pectoral fin spines in the pectoral girdle). Sounds of 15 juveniles were recorded when hand-held after three weeks of acclimation at 30 °C, 22 °C and again 30 °C. The following sound characteristics were investigated: calling activity, sound duration, fundamental frequency of drumming sounds and dominant frequency of stridulation sounds. The number of both sound types produced within the first minute of experiments did not change with temperature. In contrast, sound duration was significantly shorter at 30 °C than at 22 °C (drumming: 78-560 ms; stridulation: 23-96 ms). The fundamental frequency of drumming sounds and thus the drumming muscle contraction rate varied from 127 Hz to 242 Hz and increased with temperature. The dominant frequency of broadband stridulation sounds ranged from 1.67 kHz to 3.39 kHz and was unaffected by temperature changes. Our data demonstrate that temperature affects acoustic signaling in P. pictus, although the changes differed between sound characteristics and sound type. The effects vary from no change in calling activity and dominant frequency, to an increase in fundamental frequency and shortened duration of both sound types. Together with the known effects of temperature on hearing in the Pictus cat, the present results indicate that global warming may affect acoustic communication in fishes.
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http://dx.doi.org/10.1016/j.cbpa.2019.110589DOI Listing
February 2020

Ecology of sound communication in fishes.

Authors:
Friedrich Ladich

Fish Fish (Oxf) 2019 May 8;20(3):552-563. Epub 2019 Apr 8.

Department of Behavioural Biology University of Vienna Vienna Austria.

Fishes communicate acoustically under ecological constraints which may modify or hinder signal transmission and detection and may also be risky. This makes it important to know if and to what degree fishes can modify acoustic signalling when key ecological factors-predation pressure, noise and ambient temperature-vary. This paper reviews short-time effects of the first two factors; the third has been reviewed recently (Ladich, 2018). Numerous studies have investigated the effects of predators on fish behaviour, but only a few report changes in calling activity when hearing predator calls as demonstrated when fish responded to played-back dolphin sounds. Furthermore, swimming sounds of schooling fish may affect predators. Our knowledge on adaptations to natural changes in ambient noise, for example caused by wind or migration between quiet and noisier habitats, is limited. Hearing abilities decrease when ambient noise levels increase (termed masking), in particular in taxa possessing enhanced hearing abilities. High natural and anthropogenic noise regimes, for example vessel noise, alter calling activity in the field and laboratory. Increases in sound pressure levels (Lombard effect) and altered temporal call patterns were also observed, but no switches to higher sound frequencies. In summary, effects of predator calls and noise on sound communication are described in fishes, yet sparsely in contrast to songbirds or whales. Major gaps in our knowledge on potential negative effects of noise on acoustic communication call for more detailed investigation because fishes are keystone species in many aquatic habitats and constitute a major source of protein for humans.
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http://dx.doi.org/10.1111/faf.12368DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6519373PMC
May 2019

Sound production in female (Labyrinth fishes): comparison to males and evolutionary considerations.

Bioacoustics 2020 18;29(2):123-139. Epub 2018 Dec 18.

Department of Behavioural Biology, University of Vienna, Vienna, Austria.

Croaking gouramis (genus , Anabantoidei) generate series of two-pulsed bursts (croaks) during agonistic interactions. Sex-specific differences are minor in which raises the question whether sexes differ in the other two species. The current study analyses sounds recorded in female , compares the sound characteristics to those of males investigated earlier and correlates these characteristics to female body size. Sex-specific differences were found in three out of six sound characteristics. In females, sounds were lower in burst number, burst period and SPL. Pulse period, dominant frequency and peak-to-peak amplitude ratios of pulses did not differ between sexes. Burst period and SPL increased significantly with female body weight, whereas dominant frequency decreased. The present acoustic data indicate the sex-specific differences are more pronounced in than . The results also demonstrate that both sexes are vocal, which remains to be shown for females of the third species, , which have poorly developed sonic organs. The evolution of the pectoral sound-producing mechanism in is most likely based on an exaptation process during which acoustic signals are generated by fin tendons initially related to other functions as is evident in closely related genera lacking this organ.
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http://dx.doi.org/10.1080/09524622.2018.1555773DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7077349PMC
December 2018

Enigmatic ear stones: what we know about the functional role and evolution of fish otoliths.

Biol Rev Camb Philos Soc 2019 04 21;94(2):457-482. Epub 2018 Sep 21.

Department Biology II, Zoology, Ludwig-Maximilians-University, Großhaderner Strasse 2, 82152, Planegg-Martinsried, Germany.

Otoliths in bony fishes play an important role in the senses of balance and hearing. Otolith mass and shape are, among others, likely to be decisive factors influencing otolith motion and thus ear functioning. Yet our knowledge of how exactly these factors influence otolith motion is incomplete. In addition, experimental studies directly investigating the function of otoliths in the inner ear are scarce and yield partly conflicting results. Herein, we discuss questions and hypotheses on how otolith mass and shape, and the relationship between the sensory epithelium and overlying otolith, influence otolith motion. We discuss (i) the state-of-the-art knowledge regarding otolith function, (ii) gaps in knowledge that remain to be filled, and (iii) future approaches that may improve our understanding of the role of otoliths in ear functioning. We further link these functional questions to the evolution of solid teleost otoliths instead of numerous tiny otoconia as found in most other vertebrates. Until now, the selective forces and/or constraints driving the evolution of solid calcareous otoliths and their diversity in shape in teleosts are largely unknown. Based on a data set on the structure of otoliths and otoconia in more than 160 species covering the main vertebrate groups, we present a hypothetical framework for teleost otolith evolution. We suggest that the advent of solid otoliths may have initially been a selectively neutral 'by-product' of other key innovations during teleost evolution. The teleost-specific genome duplication event may have paved the way for diversification in otolith shape. Otolith shapes may have evolved along with the considerable diversity of, and improvements in, auditory abilities in teleost fishes. However, phenotypic plasticity may also play an important role in the creation of different otolith types, and different portions of the otolith may show different degrees of phenotypic plasticity. Future studies should thus adopt a phylogenetic perspective and apply comparative and methodologically integrative approaches, including fossil otoliths, when investigating otoconia/otolith evolution and their function in the inner ear.
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http://dx.doi.org/10.1111/brv.12463DOI Listing
April 2019

In-situ visualization of sound-induced otolith motion using hard X-ray phase contrast imaging.

Sci Rep 2018 02 15;8(1):3121. Epub 2018 Feb 15.

Ludwig-Maximilians-University Munich, Department Biology II, Zoology, Großhaderner Straße 2, 82152, Planegg-Martinsried, Germany.

Regarding the basics of ear structure-function relationships in fish, the actual motion of the solid otolith relative to the underlying sensory epithelium has rarely been investigated. Otolith motion has been characterized based on a few experimental studies and on approaches using mathematical modeling, which have yielded partially conflicting results. Those studies either predicted a simple back-and-forth motion of the otolith or a shape-dependent, more complex motion. Our study was designed to develop and test a new set-up to generate experimental data on fish otolith motion in-situ. Investigating the basic parameters of otolith motion requires an approach with high spatial and temporal resolution. We therefore used hard X-ray phase contrast imaging (XPCI). We compared two anatomically well-studied cichlid species, Steatocranus tinanti and Etroplus maculatus, which, among other features, differ in the 3D shape of their otoliths. In a water-filled tank, we presented a pure tone of 200 Hz to 1) isolated otoliths embedded in agarose serving as a simple model or 2) to a fish (otoliths in-situ). Our new set-up successfully visualized the motion of otoliths in-situ and therefore paves the way for future studies evaluating the principles of otolith motion.
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http://dx.doi.org/10.1038/s41598-018-21367-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5814409PMC
February 2018

Acoustic communication in terrestrial and aquatic vertebrates.

J Exp Biol 2017 07;220(Pt 13):2306-2317

Konrad Lorenz-Institute of Comparative Ethology, Department of Integrative Biology and Evolution, University of Veterinary Medicine, Vienna 1160, Austria.

Sound propagates much faster and over larger distances in water than in air, mainly because of differences in the density of these media. This raises the question of whether terrestrial (land mammals, birds) and (semi-)aquatic animals (frogs, fishes, cetaceans) differ fundamentally in the way they communicate acoustically. Terrestrial vertebrates primarily produce sounds by vibrating vocal tissue (folds) directly in an airflow. This mechanism has been modified in frogs and cetaceans, whereas fishes generate sounds in quite different ways mainly by utilizing the swimbladder or pectoral fins. On land, vertebrates pick up sounds with light tympana, whereas other mechanisms have had to evolve underwater. Furthermore, fishes differ from all other vertebrates by not having an inner ear end organ devoted exclusively to hearing. Comparing acoustic communication within and between aquatic and terrestrial vertebrates reveals that there is no 'aquatic way' of sound communication, as compared with a more uniform terrestrial one. Birds and mammals display rich acoustic communication behaviour, which reflects their highly developed cognitive and social capabilities. In contrast, acoustic signaling seems to be the exception in fishes, and is obviously limited to short distances and to substrate-breeding species, whereas all cetaceans communicate acoustically and, because of their predominantly pelagic lifestyle, exploit the benefits of sound propagation in a dense, obstacle-free medium that provides fast and almost lossless signal transmission.
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http://dx.doi.org/10.1242/jeb.132944DOI Listing
July 2017

Diversity of Inner Ears in Fishes: Possible Contribution Towards Hearing Improvements and Evolutionary Considerations.

Adv Exp Med Biol 2016 ;877:341-91

Department of Behavioural Biology, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.

Fishes have evolved the largest diversity of inner ears among vertebrates. While G. Retzius introduced us to the diversity of the gross morphology of fish ears in the late nineteenth century, it was A. N. Popper who unraveled the large variety of the fine structure during the last four decades. Modifications of the basic inner ear structure-consisting of three semicircular canals and their sensory epithelia, the cristae and three otolithic end organs (utricle, saccule, lagena) including the maculae-mainly relate to the saccule and lagena and the respective sensory epithelia, the macula sacculi and macula lagenae. Despite the profound morphological knowledge of inner ears and the morphological variability, the functional significance of this diversity is still largely unknown. The aims of this review are therefore twofold. First it provides an update of the state of the art of inner ear diversity in bony fishes. Second it summarizes and discusses hypotheses on the evolution of this diversity as well as formulates open questions and promising approaches to tackle these issues.
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http://dx.doi.org/10.1007/978-3-319-21059-9_16DOI Listing
April 2016

Peripheral Hearing Structures in Fishes: Diversity and Sensitivity of Catfishes and Cichlids.

Authors:
Friedrich Ladich

Adv Exp Med Biol 2016 ;877:321-40

Department of Behavioural Biology, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.

Fishes have evolved an astonishing diversity of peripheral (accessory/ancillary) auditory structures to improve hearing based on their ability to transmit oscillations of gas bladder walls to the inner ears. So far it is unclear to what degree the size of the bladder and the linkage to the ear affect hearing in fishes. An interfamilial study in catfishes revealed that families which possess large, single swim bladders and one to four Weberian ossicles were more sensitive at higher frequencies (≥1 kHz) than families which have small, paired, and encapsulated bladders and one to two ossicles. An intrafamilial investigation in thorny catfishes (family Doradidae) revealed that small differences in bladder morphology did not affect hearing similarly. Members of the cichlid family possess an even larger variation in peripheral auditory structures than catfishes. The linkage between the swim bladder and ear can either be present via anterior extensions of the bladder or be completely absent (in contrast to catfishes). Representatives having large bladders with extensions had the best sensitivities. Cichlids lacking extensions had lower sensitivities above 0.3 kHz. Species with a vestigial swim bladder exhibited a smaller hearing bandwidth than those with larger swim bladder (maximum frequency: 0.7 kHz vs. 3 kHz). Catfishes and cichlids reveal that larger gas bladders and more pronounced connections between the swim bladder and the inner ear result in improved hearing at higher frequencies. The lack of a connection between a large bladder and the inner ear does not necessarily result in a smaller detectable frequency range.
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http://dx.doi.org/10.1007/978-3-319-21059-9_15DOI Listing
April 2016

Sex-specific differences in agonistic behaviour, sound production and auditory sensitivity in the callichthyid armoured catfish Megalechis thoracata.

PLoS One 2015 16;10(3):e0121219. Epub 2015 Mar 16.

Department of Behavioural Biology, University of Vienna, Vienna, Austria.

Background: Data on sex-specific differences in sound production, acoustic behaviour and hearing abilities in fishes are rare. Representatives of numerous catfish families are known to produce sounds in agonistic contexts (intraspecific aggression and interspecific disturbance situations) using their pectoral fins. The present study investigates differences in agonistic behaviour, sound production and hearing abilities in males and females of a callichthyid catfish.

Methodology/principal Findings: Eight males and nine females of the armoured catfish Megalechis thoracata were investigated. Agonistic behaviour displayed during male-male and female-female dyadic contests and sounds emitted were recorded, sound characteristics analysed and hearing thresholds measured using the auditory evoked potential (AEP) recording technique. Male pectoral spines were on average 1.7-fold longer than those of same-sized females. Visual and acoustic threat displays differed between sexes. Males produced low-frequency harmonic barks at longer distances and thumps at close distances, whereas females emitted broad-band pulsed crackles when close to each other. Female aggressive sounds were significantly shorter than those of males (167 ms versus 219 to 240 ms) and of higher dominant frequency (562 Hz versus 132 to 403 Hz). Sound duration and sound level were positively correlated with body and pectoral spine length, but dominant frequency was inversely correlated only to spine length. Both sexes showed a similar U-shaped hearing curve with lowest thresholds between 0.2 and 1 kHz and a drop in sensitivity above 1 kHz. The main energies of sounds were located at the most sensitive frequencies.

Conclusions/significance: Current data demonstrate that both male and female M. thoracata produce aggressive sounds, but the behavioural contexts and sound characteristics differ between sexes. Sexes do not differ in hearing, but it remains to be clarified if this is a general pattern among fish. This is the first study to describe sex-specific differences in agonistic behaviour in fishes.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0121219PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4361709PMC
October 2015

Effect of temperature on acoustic communication: sound production in the croaking gourami (labyrinth fishes).

Comp Biochem Physiol A Mol Integr Physiol 2015 Apr 26;182:8-13. Epub 2014 Nov 26.

Department of Behavioural Biology, University of Vienna, Vienna, Austria.

Sound communication comprising the production and detection of acoustic signals is affected by ambient temperature in ectothermic animals. In the present study we investigated the effects of temperature on sound production and characteristics in the croaking gourami Trichopsis vittata, a freshwater fish from Southeast Asia possessing a highly specialized sound-generating mechanism found only in a single genus. The croaking gourami produces pulsed sounds by stretching and plucking two enhanced pectoral fin tendons during rapid pectoral fin beating. Croaking sounds typically consist of a series of double-pulsed bursts with main energies between 1 and 1.5 kHz. Sounds were recorded during dyadic contests between two males at three different temperatures (25°, 30° and 35°C). The mean dominant frequency increased with rising temperature from 1.18 to 1.33 kHz, whereas temporal characteristics decreased. The sound interval dropped from 492 to 259 ms, the burst period from 51 to 35 ms and the pulse period from 5.8 to 5.1 ms. In contrast, the number of sounds and number of bursts within a sound were not affected by temperature. The current study shows that spectral and temporal characteristics of sounds are affected in different ways by temperature in the croaking gourami, whereas the numbers of sounds and bursts remain unaffected. We conclude that acoustic communication in gouramis is affected by changes in ambient temperature.
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http://dx.doi.org/10.1016/j.cbpa.2014.11.013DOI Listing
April 2015

Distress sounds of thorny catfishes emitted underwater and in air: characteristics and potential significance.

J Exp Biol 2014 Nov 29;217(Pt 22):4068-78. Epub 2014 Sep 29.

Department of Behavioural Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria

Thorny catfishes produce stridulation (SR) sounds using their pectoral fins and drumming (DR) sounds via a swimbladder mechanism in distress situations when hand held in water and in air. It has been argued that SR and DR sounds are aimed at different receivers (predators) in different media. The aim of this study was to analyse and compare sounds emitted in both air and water in order to test different hypotheses on the functional significance of distress sounds. Five representatives of the family Doradidae were investigated. Fish were hand held and sounds emitted in air and underwater were recorded (number of sounds, sound duration, dominant and fundamental frequency, sound pressure level and peak-to-peak amplitudes). All species produced SR sounds in both media, but DR sounds could not be recorded in air for two species. Differences in sound characteristics between media were small and mainly limited to spectral differences in SR. The number of sounds emitted decreased over time, whereas the duration of SR sounds increased. The dominant frequency of SR and the fundamental frequency of DR decreased and sound pressure level of SR increased with body size across species. The hypothesis that catfish produce more SR sounds in air and more DR sounds in water as a result of different predation pressure (birds versus fish) could not be confirmed. It is assumed that SR sounds serve as distress sounds in both media, whereas DR sounds might primarily be used as intraspecific communication signals in water in species possessing both mechanisms.
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http://dx.doi.org/10.1242/jeb.110957DOI Listing
November 2014

Effects of temperature on auditory sensitivity in eurythermal fishes: common carp Cyprinus carpio (Family Cyprinidae) versus Wels catfish Silurus glanis (family Siluridae).

PLoS One 2014 25;9(9):e108583. Epub 2014 Sep 25.

Department of Behavioural Biology, University of Vienna, Vienna, Austria.

Background: In ectothermal animals such as fish, -temperature affects physiological and metabolic processes. This includes sensory organs such as the auditory system. The reported effects of temperature on hearing in eurythermal otophysines are contradictory. We therefore investigated the effect on the auditory system in species representing two different orders.

Methodology/principal Findings: Hearing sensitivity was determined using the auditory evoked potentials (AEP) recording technique. Auditory sensitivity and latency in response to clicks were measured in the common carp Cyprinus carpio (order Cypriniformes) and the Wels catfish Silurus glanis (order Siluriformes) after acclimating fish for at least three weeks to two different water temperatures (15°C, 25°C and again 15°C). Hearing sensitivity increased with temperature in both species. Best hearing was detected between 0.3 and 1 kHz at both temperatures. The maximum increase occurred at 0.8 kHz (7.8 dB) in C. carpio and at 0.5 kHz (10.3 dB) in S. glanis. The improvement differed between species and was in particular more pronounced in the catfish at 4 kHz. The latency in response to single clicks was measured from the onset of the sound stimulus to the most constant positive peak of the AEP. The latency decreased at the higher temperature in both species by 0.37 ms on average.

Conclusions/significance: The current study shows that higher temperature improves hearing (lower thresholds, shorter latencies) in eurythermal species from different orders of otophysines. Differences in threshold shifts between eurythermal species seem to reflect differences in absolute sensitivity at higher frequencies and they furthermore indicate differences to stenothermal (tropical) species.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0108583PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4177911PMC
December 2015

Fish bioacoustics.

Authors:
Friedrich Ladich

Curr Opin Neurobiol 2014 Oct 23;28:121-7. Epub 2014 Jul 23.

Department of Behavioural Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria. Electronic address:

Bony fishes have evolved a diversity of sound generating mechanisms and produce a variety of sounds. By contrast to sound generating mechanisms, which are lacking in several taxa, all fish species possess inner ears for sound detection. Fishes may also have various accessory structures such as auditory ossicles to improve hearing. The distribution of sound generating mechanisms and accessory hearing structures among fishes indicates that acoustic communication was not the driving force in their evolution. It is proposed here that different constraints influenced hearing and sound production during fish evolution, namely certain life history traits (territoriality, mate attraction) in the case of sound generating mechanisms, and adaptation to different soundscapes (ambient noise conditions) in accessory hearing structures (Ecoacoustical constraints hypothesis).
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http://dx.doi.org/10.1016/j.conb.2014.06.013DOI Listing
October 2014

Are accessory hearing structures linked to inner ear morphology? Insights from 3D orientation patterns of ciliary bundles in three cichlid species.

Front Zool 2014 Mar 19;11(1):25. Epub 2014 Mar 19.

Department Biology II, Zoology, Ludwig-Maximilians-University, Martinsried, Germany.

Background: Cichlid fishes show considerable diversity in swim bladder morphology. In members of the subfamily Etroplinae, the connection between anterior swim bladder extensions and the inner ears enhances sound transmission and translates into an improved hearing ability. We tested the hypothesis that those swim bladder modifications coincide with differences in inner ear morphology and thus compared Steatocranus tinanti (vestigial swim bladder), Hemichromis guttatus (large swim bladder without extensions), and Etroplus maculatus (intimate connection between swim bladder and inner ears).

Methodology And Results: We applied immunostaining together with confocal imaging and scanning electron microscopy for the investigation of sensory epithelia, and high-resolution, contrast-enhanced microCT imaging for characterizing inner ears in 3D, and evaluated otolith dimensions. Compared to S. tinanti and H. guttatus, inner ears of E. maculatus showed an enlargement of all three maculae, and a particularly large lacinia of the macula utriculi. While our analysis of orientation patterns of ciliary bundles on the three macula types using artificially flattened maculae uncovered rather similar orientation patterns of ciliary bundles, interspecific differences became apparent when illustrating the orientation patterns on the 3D models of the maculae: differences in the shape and curvature of the lacinia of the macula utriculi, and the anterior arm of the macula lagenae resulted in an altered arrangement of ciliary bundles.

Conclusions: Our results imply that improved audition in E. maculatus is associated not only with swim bladder modifications but also with altered inner ear morphology. However, not all modifications in E. maculatus could be connected to enhanced auditory abilities, and so a potential improvement of the vestibular sense, among others, also needs to be considered. Our study highlights the value of analyzing orientation patterns of ciliary bundles in their intact 3D context in studies of inner ear morphology and physiology.
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http://dx.doi.org/10.1186/1742-9994-11-25DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3999956PMC
March 2014

A unique swim bladder-inner ear connection in a teleost fish revealed by a combined high-resolution microtomographic and three-dimensional histological study.

BMC Biol 2013 Jul 4;11:75. Epub 2013 Jul 4.

Department of Behavioural Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.

Background: In most modern bony fishes (teleosts) hearing improvement is often correlated with a close morphological relationship between the swim bladder or other gas-filled cavities and the saccule or more rarely with the utricle. A connection of an accessory hearing structure to the third end organ, the lagena, has not yet been reported. A recent study in the Asian cichlid Etroplus maculatus provided the first evidence that a swim bladder may come close to the lagena. Our study was designed to uncover the swim bladder-inner ear relationship in this species. We used a new approach by applying a combination of two high-resolution techniques, namely microtomographic (microCT) imaging and histological serial semithin sectioning, providing the basis for subsequent three-dimensional reconstructions. Prior to the morphological study, we additionally measured auditory evoked potentials at four frequencies (0.5, 1, 2, 3 kHz) to test the hearing abilities of the fish.

Results: E. maculatus revealed a complex swim bladder-inner ear connection in which a bipartite swim bladder extension contacts the upper as well as the lower parts of each inner ear, a condition not observed in any other teleost species studied so far. The gas-filled part of the extension is connected to the lagena via a thin bony lamella and is firmly attached to this bony lamella with connective material. The second part of the extension, a pad-like structure, approaches the posterior and horizontal semicircular canals and a recessus located posterior to the utricle.

Conclusions: Our study is the first detailed report of a link between the swim bladder and the lagena in a teleost species. We suggest that the lagena has an auditory function in this species because the most intimate contact exists between the swim bladder and this end organ. The specialized attachment of the saccule to the cranial bone and the close proximity of the swim bladder extension to the recessus located posterior to the utricle indicate that the saccule and the utricle also receive parallel inputs from the swim bladder extension. We further showed that a combination of non-destructive microCT imaging with histological analyses on the same specimen provides a powerful tool to decipher and interpret fine structures and to compensate for methodological artifacts.
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http://dx.doi.org/10.1186/1741-7007-11-75DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3720219PMC
July 2013

Does the hearing sensitivity in thorny catfishes depend on swim bladder morphology?

PLoS One 2013 25;8(6):e67049. Epub 2013 Jun 25.

Department of Behavioural Biology, University of Vienna, Vienna, Austria.

Background: Thorny catfishes exhibit large variations in swim bladder morphology. These organs are of different sizes, forms and may have simple or branched diverticula. The swim bladder plays an important role in otophysans because it enhances their hearing sensitivity by transmitting sound pressure fluctuations via ossicles to the inner ear.

Methodology/principal Findings: To investigate if a form-function relationship exists, the swim bladder morphology and hearing ability were analyzed in six species. The morphology was quantified by measuring the length, width and height and calculating a standardized swim bladder length (sSBL), which was then used to calculate the relative swim bladder length (rSBL). Hearing was measured using the auditory evoked potential (AEP) recording technique. Two species had simple apple-shaped and four species heart-shaped (cordiform) bladders. One of the latter species had short unbranched diverticula on the terminal margin, two had a secondary bladder and two had many long, branched diverticula. The rSBL differed significantly between most of the species. All species were able to detect frequencies between 70 Hz and 6 kHz, with lowest thresholds found between 0.5 and 1 kHz (60 dB re 1 µPa). Hearing curves were U-shaped except in Hemidoras morrisi in which it was ramp-like. Mean hearing thresholds of species possessing smaller rSBLs were slightly lower (maximum 8.5 dB) than those of species having larger rSBLs.

Conclusions/significance: The current findings reveal a relationship between swim bladder form and its function among thorny catfishes. Relatively smaller swim bladders resulted in relatively better hearing. This is in contrast to a prior inter-familial study on catfishes in which species with large unpaired bladders possessed higher sensitivity at higher frequencies than species having tiny paired and encapsulated bladders.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0067049PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3692464PMC
February 2014

Hearing in cichlid fishes under noise conditions.

PLoS One 2013 28;8(2):e57588. Epub 2013 Feb 28.

Department of Behavioural Biology, University of Vienna, Vienna, Austria.

Background: Hearing thresholds of fishes are typically acquired under laboratory conditions. This does not reflect the situation in natural habitats, where ambient noise may mask their hearing sensitivities. In the current study we investigate hearing in terms of sound pressure (SPL) and particle acceleration levels (PAL) of two cichlid species within the naturally occurring range of noise levels. This enabled us to determine whether species with and without hearing specializations are differently affected by noise.

Methodology/principal Findings: We investigated auditory sensitivities in the orange chromide Etroplus maculatus, which possesses anterior swim bladder extensions, and the slender lionhead cichlid Steatocranus tinanti, in which the swim bladder is much smaller and lacks extensions. E. maculatus was tested between 0.2 and 3kHz and S. tinanti between 0.1 and 0.5 kHz using the auditory evoked potential (AEP) recording technique. In both species, SPL and PAL audiograms were determined in the presence of quiet laboratory conditions (baseline) and continuous white noise of 110 and 130 dB RMS. Baseline thresholds showed greatest hearing sensitivity around 0.5 kHz (SPL) and 0.2 kHz (PAL) in E. maculatus and 0.2 kHz in S. tinanti. White noise of 110 dB elevated the thresholds by 0-11 dB (SPL) and 7-11 dB (PAL) in E. maculatus and by 1-2 dB (SPL) and by 1-4 dB (PAL) in S. tinanti. White noise of 130 dB elevated hearing thresholds by 13-29 dB (SPL) and 26-32 dB (PAL) in E. maculatus and 6-16 dB (SPL) and 6-19 dB (PAL) in S. tinanti.

Conclusions: Our data showed for the first time for SPL and PAL thresholds that the specialized species was masked by different noise regimes at almost all frequencies, whereas the non-specialized species was much less affected. This indicates that noise can limit sound detection and acoustic orientation differently within a single fish family.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0057588PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3585214PMC
August 2013

Auditory evoked potential audiometry in fish.

Rev Fish Biol Fish 2013;23(3):317-364. Epub 2013 Jan 18.

Marine Laboratory, Woods Hole, MA 02543 USA ; 179 Woods Hole Rd., Falmouth, MA 02540 USA.

A recent survey lists more than 100 papers utilizing the auditory evoked potential (AEP) recording technique for studying hearing in fishes. More than 95 % of these AEP-studies were published after Kenyon et al. introduced a non-invasive electrophysiological approach in 1998 allowing rapid evaluation of hearing and repeated testing of animals. First, our review compares AEP hearing thresholds to behaviorally gained thresholds. Second, baseline hearing abilities are described and compared in 111 fish species out of 51 families. Following this, studies investigating the functional significance of various accessory hearing structures (Weberian ossicles, swim bladder, otic bladders) by eliminating these morphological structures in various ways are dealt with. Furthermore, studies on the ontogenetic development of hearing are summarized. The AEP-technique was frequently used to study the effects of high sound/noise levels on hearing in particular by measuring the temporary threshold shifts after exposure to various noise types (white noise, pure tones and anthropogenic noises). In addition, the hearing thresholds were determined in the presence of noise (white, ambient, ship noise) in several studies, a phenomenon termed masking. Various ecological (e.g., temperature, cave dwelling), genetic (e.g., albinism), methodical (e.g., ototoxic drugs, threshold criteria, speaker choice) and behavioral (e.g., dominance, reproductive status) factors potentially influencing hearing were investigated. Finally, the technique was successfully utilized to study acoustic communication by comparing hearing curves with sound spectra either under quiet conditions or in the presence of noise, by analyzing the temporal resolution ability of the auditory system and the detection of temporal, spectral and amplitude characteristics of conspecific vocalizations.
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http://dx.doi.org/10.1007/s11160-012-9297-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4560088PMC
January 2013

Relationship between swim bladder morphology and hearing abilities--a case study on Asian and African cichlids.

PLoS One 2012 7;7(8):e42292. Epub 2012 Aug 7.

Department of Behavioral Biology, University of Vienna, Vienna, Austria.

Background: Several teleost species have evolved anterior extensions of the swim bladder which come close to or directly contact the inner ears. A few comparative studies have shown that these morphological specializations may enhance hearing abilities. This study investigates the diversity of swim bladder morphology in four Asian and African cichlid species and analyzes how this diversity affects their hearing sensitivity.

Methodology/principal Findings: We studied swim bladder morphology by dissections and by making 3D reconstructions from high-resolution microCT scans. The auditory sensitivity was determined in terms of sound pressure levels (SPL) and particle acceleration levels (PAL) using the auditory evoked potential (AEP) recording technique. The swim bladders in Hemichromis guttatus and Steatocranus tinanti lacked anterior extensions and the swim bladder was considerably small in the latter species. In contrast, Paratilapia polleni and especially Etroplus maculatus possessed anterior extensions bringing the swim bladder close to the inner ears. All species were able to detect frequencies up to 3 kHz (SPL) except S. tinanti which only responded to frequencies up to 0.7 kHz. P. polleni and E. maculatus showed significantly higher auditory sensitivities at 0.5 and 1 kHz than the two species lacking anterior swim bladder extensions. The highest auditory sensitivities were found in E. maculatus, which possessed the most intimate swim bladder-inner ear relationship (maximum sensitivity 66 dB re 1 µPa at 0.5 kHz).

Conclusions: Our results indicate that anterior swim bladder extensions seem to improve mean absolute auditory sensitivities by 21-42 dB (SPLs) and 21-36 dB (PALs) between 0.5 and 1 kHz. Besides anterior extensions, the size of the swim bladder appears to be an important factor for extending the detectable frequency range (up to 3 kHz).
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0042292PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3413697PMC
January 2013

Effects of temperature on sound production and auditory abilities in the Striped Raphael catfish Platydoras armatulus (Family Doradidae).

PLoS One 2011 17;6(10):e26479. Epub 2011 Oct 17.

Department of Behavioural Biology, University of Vienna, Vienna, Austria.

Background: Sound production and hearing sensitivity of ectothermic animals are affected by the ambient temperature. This is the first study investigating the influence of temperature on both sound production and on hearing abilities in a fish species, namely the neotropical Striped Raphael catfish Platydoras armatulus.

Methodology/principal Findings: Doradid catfishes produce stridulation sounds by rubbing the pectoral spines in the shoulder girdle and drumming sounds by an elastic spring mechanism which vibrates the swimbladder. Eight fish were acclimated for at least three weeks to 22°, then to 30° and again to 22°C. Sounds were recorded in distress situations when fish were hand-held. The stridulation sounds became shorter at the higher temperature, whereas pulse number, maximum pulse period and sound pressure level did not change with temperature. The dominant frequency increased when the temperature was raised to 30°C and the minimum pulse period became longer when the temperature decreased again. The fundamental frequency of drumming sounds increased at the higher temperature. Using the auditory evoked potential (AEP) recording technique, the hearing thresholds were tested at six different frequencies from 0.1 to 4 kHz. The temporal resolution was determined by analyzing the minimum resolvable click period (0.3-5 ms). The hearing sensitivity was higher at the higher temperature and differences were more pronounced at higher frequencies. In general, latencies of AEPs in response to single clicks became shorter at the higher temperature, whereas temporal resolution in response to double-clicks did not change.

Conclusions/significance: These data indicate that sound characteristics as well as hearing abilities are affected by temperatures in fishes. Constraints imposed on hearing sensitivity at different temperatures cannot be compensated even by longer acclimation periods. These changes in sound production and detection suggest that acoustic orientation and communication are affected by temperature changes in the neotropical catfish P. armatulus.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0026479PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3195728PMC
February 2012

Ontogenetic development of weberian ossicles and hearing abilities in the African bullhead catfish.

PLoS One 2011 Apr 12;6(4):e18511. Epub 2011 Apr 12.

Department of Behavioural Biology, University of Vienna, Vienna, Austria.

Background: The weberian apparatus of otophysine fishes facilitates sound transmission from the swimbladder to the inner ear to increase hearing sensitivity. It has been of great interest to biologists since the 19(th) century. No studies, however, are available on the development of the weberian ossicles and its effect on the development of hearing in catfishes.

Methodology/principal Findings: We investigated the development of the weberian apparatus and auditory sensitivity in the catfish Lophiobagrus cyclurus. Specimens from 11.3 mm to 85.5 mm in standard length were studied. Morphology was assessed using sectioning, histology, and X-ray computed tomography, along with 3D reconstruction. Hearing thresholds were measured utilizing the auditory evoked potentials recording technique. Weberian ossicles and interossicular ligaments were fully developed in all stages investigated except in the smallest size group. In the smallest catfish, the intercalarium and the interossicular ligaments were still missing and the tripus was not yet fully developed. Smallest juveniles revealed lowest auditory sensitivity and were unable to detect frequencies higher than 2 or 3 kHz; sensitivity increased in larger specimens by up to 40 dB, and frequency detection up to 6 kHz. In the size groups capable of perceiving frequencies up to 6 kHz, larger individuals had better hearing abilities at low frequencies (0.05-2 kHz), whereas smaller individuals showed better hearing at the highest frequencies (4-6 kHz).

Conclusions/significance: Our data indicate that the ability of otophysine fish to detect sounds at low levels and high frequencies largely depends on the development of the weberian apparatus. A significant increase in auditory sensitivity was observed as soon as all weberian ossicles and interossicular ligaments are present and the chain for transmitting sounds from the swimbladder to the inner ear is complete. This contrasts with findings in another otophysine, the zebrafish, where no threshold changes have been observed.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0018511PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3075255PMC
April 2011

Year-round variability of ambient noise in temperate freshwater habitats and its implications for fishes.

Aquat Sci 2010 Jun;72(3):371-378

Department of Behavioural Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria,

Changes in habitat acoustics over the year can potentially affect fish hearing and orientation to sound, especially in temperate climates. This is the first study where year-round changes in ambient noise in aquatic habitats were assessed. Seven different European fresh-water habitats were chosen for this study. Sound pressure level (SPL) and spectral composition of the ambient noise varied in both quiet stagnant habitats (lakes, backwaters) and in flowing habitats (streams, rivers). Linear equivalent SPL (L(Leq, 60s)) tended to be lower in stagnant habitats (means: 91.6-111.7 dB) than in flowing habitats (means: 111.2-133.4 dB). The changes in SPL were smallest in the river (means: 4.2-4.4 dB, maxima: 8.5-10.1 dB), whereas significantly higher values were measured in stagnant habitats and the stream (means: 9.9-14.9 dB, maxima: 25.1-30.9 dB). The spectral compositions of the ambient noise determined at different times of the year were highly correlated to each other at the river sites (mean cross-correlation coefficients: 0.85 and 0.94) and were weaker or not correlated at the other study sites (means: 0.24-0.76). The changes in ambient noise spectra were negatively correlated to changes in SPL, indicating that large changes in SPLs were accompanied by large changes in spectral composition and vice versa. Comparison of these ecoacoustical data with a preceding study (Amoser and Ladich in J Exp Biol 208:3533-3542, 2005) indicates that the auditory sensitivity in hearing specialists is affected by changes in ambient noise levels and spectra throughout a year and that this effect tends to be more pronounced in stagnant waters and the stream than at river sites. On the other hand, absolute noise levels result in a higher degree of masking in flowing waters.
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http://dx.doi.org/10.1007/s00027-010-0136-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2948566PMC
June 2010

Representation of complex vocalizations in the Lusitanian toadfish auditory system: evidence of fine temporal, frequency and amplitude discrimination.

Proc Biol Sci 2011 Mar 22;278(1707):826-34. Epub 2010 Sep 22.

Departamento de Biologia Animal, Centro de Biologia Ambiental, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal.

Many fishes rely on their auditory skills to interpret crucial information about predators and prey, and to communicate intraspecifically. Few studies, however, have examined how complex natural sounds are perceived in fishes. We investigated the representation of conspecific mating and agonistic calls in the auditory system of the Lusitanian toadfish Halobatrachus didactylus, and analysed auditory responses to heterospecific signals from ecologically relevant species: a sympatric vocal fish (meagre Argyrosomus regius) and a potential predator (dolphin Tursiops truncatus). Using auditory evoked potential (AEP) recordings, we showed that both sexes can resolve fine features of conspecific calls. The toadfish auditory system was most sensitive to frequencies well represented in the conspecific vocalizations (namely the mating boatwhistle), and revealed a fine representation of duration and pulsed structure of agonistic and mating calls. Stimuli and corresponding AEP amplitudes were highly correlated, indicating an accurate encoding of amplitude modulation. Moreover, Lusitanian toadfish were able to detect T. truncatus foraging sounds and A. regius calls, although at higher amplitudes. We provide strong evidence that the auditory system of a vocal fish, lacking accessory hearing structures, is capable of resolving fine features of complex vocalizations that are probably important for intraspecific communication and other relevant stimuli from the auditory scene.
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http://dx.doi.org/10.1098/rspb.2010.1376DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3049045PMC
March 2011

Otolith morphology and hearing abilities in cave- and surface-dwelling ecotypes of the Atlantic molly, Poecilia mexicana (Teleostei: Poeciliidae).

Hear Res 2010 Aug 27;267(1-2):137-48. Epub 2010 Apr 27.

Department of Earth and Environmental Sciences, Ludwig-Maximilians-University Munich, Richard-Wagner-Strasse 10, 80333 Munich, Germany.

Cave fish have rarely been investigated with regard to their inner ear morphology, hearing abilities, and acoustic communication. Based on a previous study that revealed morphological differences in the saccular otolith between a cave and two surface populations of Poecilia mexicana, we checked for additional differences in utricular and lagenar otoliths and tested whether different populations have similar hearing sensitivities. We found pronounced differences in the shape of all three otoliths. Otoliths of the saccule and lagena from cave fish differed from those of surface fish in the features of the face oriented towards the sensory epithelium. In addition, otoliths of the utricle and lagena were significantly heavier in cave fish. Auditory sensitivities were measured between 100 and 1500Hz, utilizing the auditory evoked potential recording technique. We found similar hearing abilities in cave and surface fish, with greatest sensitivity between 200 and 300Hz. An acoustic survey revealed that neither ecotype produced species-specific sounds. Our data indicate that cave dwelling altered the otolith morphology in Atlantic mollies, probably due to metabolic differences. Different otolith morphology, however, did not affect general auditory sensitivity or acoustic behavior.
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http://dx.doi.org/10.1016/j.heares.2010.04.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2905516PMC
August 2010

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

BMC Biol 2010 Jan 29;8:10. Epub 2010 Jan 29.

University of Vienna, Department of Behavioural Biology, Althanstrasse 14, 1090 Vienna, Austria.

Background: Surveys 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.

Results: The 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.

Conclusions: This 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.
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http://dx.doi.org/10.1186/1741-7007-8-10DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2824629PMC
January 2010

Sound pressure and particle acceleration audiograms in three marine fish species from the Adriatic Sea.

J Acoust Soc Am 2009 Oct;126(4):2100-7

Department of Behavioural Biology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.

Fishes show great variability in hearing sensitivity, bandwidth, and the appropriate stimulus component for the inner ear (particle motion or pressure). Here, hearing sensitivities in three vocal marine species belonging to different families were described in terms of sound pressure and particle acceleration. In particular, hearing sensitivity to tone bursts of varying frequencies were measured in the red-mouthed goby Gobius cruentatus, the Mediterranean damselfish Chromis chromis, and the brown meagre Sciaena umbra using the non-invasive auditory evoked potential-recording technique. Hearing thresholds were measured in terms of sound pressure level and particle acceleration level in the three Cartesian directions using a newly developed miniature pressure-acceleration sensor. The brown meagre showed the broadest hearing range (up to 3000 Hz) and the best hearing sensitivity, both in terms of sound pressure and particle acceleration. The red-mouthed goby and the damselfish were less sensitive, with upper frequency limits of 700 and 600 Hz, respectively. The low auditory thresholds and the large hearing bandwidth of S. umbra indicate that sound pressure may play a role in S. umbra's hearing, even though pronounced connections between the swim bladder and the inner ears are lacking.
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http://dx.doi.org/10.1121/1.3203562DOI Listing
October 2009

Effects of ambient and boat noise on hearing and communication in three fish species living in a marine protected area (Miramare, Italy).

Mar Pollut Bull 2009 Dec 8;58(12):1880-7. Epub 2009 Aug 8.

University of Trieste, Department of Biology, v. Giorgieri 7, 34127 Trieste, Italy.

The WWF-Natural Marine Reserve of Miramare (Trieste, Italy) is located in a major industrial and vacation area in the Adriatic Sea. Consequently, noise emanating from boating and shipping is an inevitable factor for local fishes. This study investigates the effects of ambient and ship noise on representatives of three vocal fish families with different hearing abilities. Ambient and ship noise were recorded, their sound pressure levels measured and played back in the lab. Auditory sensitivity was determined in Chromis chromis, Sciaena umbra and Gobius cruentatus, utilizing the auditory evoked potential recording technique. Compared to lab conditions, hearing thresholds determined during ambient noise playbacks were barely masked. Contrary, the noise emanating from a cabin-cruiser substantially reduced auditory sensitivity relative to thresholds in ambient noise. This masking effect was most pronounced in the frequency range where acoustic communication takes place. Boat noise potentially affects acoustic communication in fishes inhabiting the reserve.
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http://dx.doi.org/10.1016/j.marpolbul.2009.07.011DOI Listing
December 2009

Does speaker presentation affect auditory evoked potential thresholds in goldfish?

Comp Biochem Physiol A Mol Integr Physiol 2009 Nov 12;154(3):341-6. Epub 2009 Jul 12.

Department of Behavioural Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.

The auditory evoked potential (AEP) recording technique has proved to be a very versatile and successful approach in studying auditory sensitivities in fishes. The AEP protocol introduced by Kenyon, Ladich and Yan in 1998 using an air speaker with the fish positioned at the water surface gave auditory thresholds in goldfish very close to behavioural values published before. This approach was subsequently modified by several laboratories, raising the question whether speaker choice (air vs. underwater) or the position of subjects affect auditory threshold determination. To answer these questions, the hearing specialist Carassius auratus was measured using an air speaker, an underwater speaker and alternately positioning the fish directly at or 5cm below the water surface. Mean hearing thresholds obtained using these 4 different setups varied by 5.6dB, 3.7dB and 4dB at 200Hz, 500Hz and 1000Hz, respectively. Accordingly, pronounced differences in AEP thresholds in goldfish measured in different laboratories reflect other factors than speaker used and depth of the test subjects, namely variations in threshold definition, background noise, population differences, or calibration errors.
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http://dx.doi.org/10.1016/j.cbpa.2009.07.004DOI Listing
November 2009
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