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

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.     

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

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.     

Sensory evolution of hearing in tettigoniids with differing communication systems

In Tettigoniidae (Orthoptera: Ensifera), hearing organs are essential in mate detection. Male tettigoniids usually produce calling songs by tegminal stridulation, whereas females approach the males phonotactically. This unidirectional communication system is the most common one among tettigoniids. In several tettigoniid lineages, females have evolved acoustic replies to the male calling song which constitutes a bidirectional communication system. The genus Poecilimon (Tettigoniidae: Phaneropterinae) is of special interest because the ancestral state of bidirectional communication, with calling males and responding females, has been reversed repeatedly to unidirectional communication. Acoustic communication is mediated by hearing organs that are adapted to the conspecific signals. Therefore, we analyse the auditory system in the Tettigoniidae genus Poecilimon for functional adaptations in three characteristics: (i) dimension of sound‐receiving structures (tympanum and acoustic spiracle), (ii) number of auditory sensilla and (iii) hearing sensitivity. Profound differences in the auditory system correlate with uni‐ or bidirectional communication. Among the sound‐receiving structures, the tympana scale with body size, whereas the acoustic spiracle, the major sound input structure, was drastically reduced in unidirectional communicating species. In the unidirectional P. ampliatus group, auditory sensilla are severely reduced in numbers, but not in the unidirectional P. propinquus group. Within the P. ampliatus group, the number of auditory sensilla is further reduced in P. intermedius which lost acoustic signalling due to parthenogenesis. The auditory sensitivity correlated with the size of the acoustic spiracle, as hearing sensitivity was better with larger spiracles, especially in the ultrasonic range. Our results show a significant reduction in auditory structures, shaped by the differing sex roles during mate detection.     

Sex-Specific Differences in Agonistic Behaviour,Sound Production and Auditory Sensitivity in the Callichthyid Armoured Catfish Megalechis thoracata

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.     

Ontogeny of auditory saccular sensitivity in the plainfin midshipman fish, <Emphasis Type="Italic">Porichthys notatus</Emphasis>

The auditory system of the plainfin midshipman fish, Porichthys notatus, is an important sensory receiver system used to encode intraspecific social communication signals in adults, but the response properties and function of this receiver system in pre-adult stages are less known. In this study we examined the response properties of auditory-evoked potentials from the midshipman saccule, the main organ of hearing in this species, to determine whether the frequency response and auditory threshold of saccular hair cells to behaviorally relevant single tone stimuli change during ontogeny. Saccular potentials were recorded from three relative sizes of midshipman fish: small juveniles [1.9–3.1 cm standard length (SL), large juveniles (6.8–8.0 cm SL) and non-reproductive adults (9.0–22.6 cm SL)]. The auditory evoked potentials were recorded from the rostral, middle and caudal regions of the saccule while single tone stimuli (75–1,025 Hz) were presented via an underwater speaker. We show that the frequency response and auditory threshold of the midshipman saccule is established early in development and retained throughout ontogeny. We also show that saccular sensitivity to frequencies greater than 385 Hz increases with age/size and that the midshipman saccule of small and large juveniles, like that of non-reproductive adults, is best suited to detect low frequency sounds (<105 Hz) in their natural acoustic environment.     

Potential effects of underwater noise from wind turbines on the marbled rockfish (Sebasticus marmoratus)

Environmental assessments of underwater noise on marine species must be based on species-specific hearing abilities. This study was to assess the potential impact of underwater noise from the East China Sea Bridge wind farm on the acoustic communication of the marbled rockfish. Here, the 1/3 octave frequency band of underwater noise was 125 Hz with the level range of 78–96 dB re 1 μPa, recorded at distances between 15-20m from the foundation at wind speed of 3–5 m/s. Auditory evoked potential (AEP) and passive acoustic techniques were used to determine the hearing abilities and sound production of the fish. The resultes showed the lowest auditory threshold of Sebastiscus marmoratus was 70 dB at 150 Hz matching the disturbance sound ranging 140–180 Hz, which indicating the acoustic communication used in this species. However, the frequency and level of turbine underwater noise overlapped the auditory sensitivity and vocalization of Sebastiscus marmoratus. The wind turbine noise could be detected by fish and may have a masking effect on their acoustic communication. This result can be applied for further to the assessent of fish species released into offshore wind farm marine ranch.     

Encoding properties of auditory neurons in the brain of a soniferous damselfish: response to simple tones and complex conspecific signals

The fish auditory system encodes important acoustic stimuli used in social communication, but few studies have examined response properties of central auditory neurons to natural signals. We determined the features and responses of single hindbrain and midbrain auditory neurons to tone bursts and playbacks of conspecific sounds in the soniferous damselfish, Abudefduf abdominalis. Most auditory neurons were either silent or had slow irregular resting discharge rates <20 spikes s⁻¹. Average best frequency for neurons to tone stimuli was ~130 Hz but ranged from 80 to 400 Hz with strong phase-locking. This low-frequency sensitivity matches the frequency band of natural sounds. Auditory neurons were also modulated by playbacks of conspecific sounds with thresholds similar to 100 Hz tones, but these thresholds were lower than that of tones at other test frequencies. Thresholds of neurons to natural sounds were lower in the midbrain than the hindbrain. This is the first study to compare response properties of auditory neurons to both simple tones and complex stimuli in the brain of a recently derived soniferous perciform that lacks accessory auditory structures. These data demonstrate that the auditory fish brain is most sensitive to the frequency and temporal components of natural pulsed sounds that provide important signals for conspecific communication.     

Contribution to the study of acoustic communication in two Belgian river bullheads (<Emphasis Type="Italic">Cottus rhenanus and C. perifretum</Emphasis>) with further insight into the sound-producing mechanism

Background

The freshwater sculpins (genus Cottus) are small, bottom-living fishes widely distributed in North America and Europe. The taxonomy of European species has remained unresolved for a long time due to the overlap of morphological characters. Sound production has already been documented in some cottid representatives, with sounds being involved in courtship and agonistic interactions. Although the movements associated with sound production have been observed, the underlying mechanism remains incomplete. Here, we focus on two closely related species from Belgium: C. rhenanus and C. perifretum. This study aims 1) to record and to compare acoustic communication in both species, 2) to give further insight into the sound-producing mechanism and 3) to look for new morphological traits allowing species differentiation.

Results

Both Cottus species produce multiple-pulsed agonistic sounds using a similar acoustic pattern: the first interpulse duration is always longer, making the first pulse unit distinct from the others. Recording sound production and hearing abilities showed a clear relationship between the sound spectra and auditory thresholds in both species: the peak frequencies of calls are around 150 Hz, which corresponds to their best hearing sensitivity. However, it appears that these fishes could not hear acoustic signals produced by conspecifics in their noisy habitat considering their hearing threshold expressed as sound pressure (~ 125 dB re 1 μPa). High-speed video recordings highlighted that each sound is produced during a complete back and forth movement of the pectoral girdle.

Conclusions

Both Cottus species use an acoustic pattern that remained conserved during species diversification. Surprisingly, calls do not seem to have a communicative function. On the other hand, fish could detect substrate vibrations resulting from movements carried out during sound production. Similarities in temporal and spectral characteristics also suggest that both species share a common sound-producing mechanism, likely based on pectoral girdle vibrations. From a morphological point of view, only the shape of the spinelike scales covering the body allows species differentiation.

     

Ocean acidification boosts larval fish development but reduces the window of opportunity for successful settlement

Locating appropriate settlement habitat is a crucial step in the life cycle of most benthic marine animals. In marine fish, this step involves the use of multiple senses, including audition, olfaction and vision. To date, most investigations of larval fish audition focus on the hearing thresholds to various frequencies of sounds without testing an ecological response to such sounds. Identifying responses to biologically relevant sounds at the development stage in which orientation is most relevant is fundamental. We tested for the existence of ontogenetic windows of reception to sounds that could act as orientation cues with a focus on vulnerability to alteration by human impacts. Here we show that larvae of a catadromous fish species (barramundi, Lates calcarifer) were attracted towards sounds from settlement habitat during a surprisingly short ontogenetic window of approximately 3 days. Yet, this auditory preference was reversed in larvae reared under end-of-century levels of elevated CO₂, such that larvae are repelled from cues of settlement habitat. These future conditions also reduced the swimming speeds and heightened the anxiety levels of barramundi. Unexpectedly, an acceleration of development and onset of metamorphosis caused by elevated CO₂ were not accompanied by the earlier onset of attraction towards habitat sounds. This mismatch between ontogenetic development and the timing of orientation behaviour may reduce the ability of larvae to locate habitat or lead to settlement in unsuitable habitats. The misinterpretation of key orientation cues can have implications for population replenishment, which are only exacerbated when ontogenetic development decouples from the specific behaviours required for location of settlement habitats.     

Anatomy of the stridulation apparatus of the beech leaf‐mining weevil and characterization of,and behavioral responses to,stridulation sounds

We investigated auditory signals and morphology of the stridulatory apparatus of the European beech leaf‐mining weevil, Orchestes fagi L. (Coleoptera: Curculionidae), an invasive herbivore now established in Nova Scotia, Canada, to determine their potential for enhancing survey tools to monitor the spread of the species in Canada. We recorded and described sounds produced by adult O. fagi, analyzed the morphology of the stridulatory mechanism for intersexual differences and asymmetry, and examined behavioral responses elicited in conspecifics by playback of stridulation recordings. Adult O. fagi produced sounds under three conditions: male in distress, female in distress, and male in the presence of female. Female distress chirps lasted significantly longer than male distress chirps and male chirps in the presence of females, but peak frequencies and mean number of chirps per s did not differ significantly among the three groups. Morphology of the stridulation structures in male and female O. fagi was compared using scanning electron microscopy. Orchestes fagi have an elytro‐tergal file‐ and scraper‐type sound production apparatus, through which sound is produced upon anterior motion of the abdomen. Female O. fagi have a ‘pars stridens’ that is longer and has more ridges than males. Width and number of ridges per length of pars stridens did not differ between the sexes. Evidence of asymmetry was found in male pars stridens, with the right side being longer than the left. Playback of recorded sounds to adult weevils suggests female O. fagi were repelled by sounds produced by distressed males.     

The ontogenetic development of auditory sensitivity, vocalization and acoustic communication in the labyrinth fish Trichopsis vittata

The anabantoid fish Trichopsis vittata starts vocalizing as 8-week-old juveniles. In order to determine whether juveniles are able to detect conspecific sounds, hearing sensitivities were measured in six size groups utilizing the auditory brainstem response-recording technique. Results were compared to sound pressure levels and spectra of sounds recorded during fighting. Auditory evoked potentials were present in all size groups and complete audiograms were obtained starting with 0.18 to 0.30 g juveniles. Auditory sensitivity during development primarily increased between 0.8 kHz and 3.0 kHz. The most sensitive frequency within this range shifted from 2.5 kHz to 1.5 kHz, whereas thresholds decreased by 14 dB. Sound production, on the other hand, started at 0.1 g and sound power spectra at dominant frequencies increased by 43 dB, while dominant frequencies shifted from 3 kHz to 1.5 kHz. Comparisons between audiograms and sound power spectra in similar-sized juveniles revealed no clear match between most sensitive frequencies and dominant frequencies of sounds. This also revealed that juveniles cannot detect conspecific sounds below the 0.31 to 0.65 g size class. These results indicate that auditory sensitivity develops prior to the ability to vocalize and that vocalization occurs prior to the ability to communicate acoustically.     

Correlation between auditory sensitivity and vocalization in anabantoid fishes

Several anabantoid species produce broad-band sounds with high-pitched dominant frequencies (0.8–2.5 kHz), which contrast with generally low-frequency hearing abilities in (perciform) fishes. Utilizing a recently developed auditory brainstem response recording-technique, auditory sensitivities of the gouramis Trichopsis vittata, T. pumila, Colisa lalia, Macropodus opercularis and Trichogaster trichopterus were investigated and compared with the sound characteristics of the respective species. All five species exhibited enhanced sound-detecting abilities and perceived tone bursts up to 5 kHz, which qualifies this group as hearing specialists. All fishes possessed a high-frequency sensitivity maximum between 800 Hz and 1500 Hz. Lowest hearing thresholds were found in T. trichopterus (76 dB re 1 μPa at 800 Hz). Dominant frequencies of sounds correspond with the best hearing bandwidth in T. vittata (1–2 kHz) and C. lalia (0.8–1 kHz). In the smallest species, T. pumila, dominant frequencies of acoustic signals (1.5–2.5 kHz) do not match lowest thresholds, which were below 1.5 kHz. However, of all species studied, T. pumila had best hearing sensitivity at frequencies above 2 kHz. The association between high-pitched sounds and hearing may be caused by the suprabranchial air-breathing chamber, which, lying close to the hearing and sonic organs, enhances both sound perception and emission at its resonant frequency. Accepted: 26 November 1997     

Analysis of the Stridulation in Solifuges (Arachnida: Solifugae)

Stridulation in solifuges has not been investigated yet. We performed a comparative analysis of the stridulatory organs and sounds produced by juveniles of various developmental stages and adults (both sexes) of Galeodes caspius subfuscus Birula. The stridulatory organ is of similar morphology in all developmental stages. The sound that they produced was a broad frequency hissing, composed of one or two chirps with maximum at 2.4 kHz. The intensity of the sound was found to increase with body size. Otherwise, no differences were observed between stridulation in juvenile, male and female individuals. Therefore, we suggest that the stridulation in solifuges has primarily a defensive role. As solifuges are neither venomous nor unpalatable, they might imitate an accoustically aposematic organism that shares the same habitat and has similar circadian activity, e.g. vipers. It may also have an intraspecific function in reduction of cannibalistic tendencies.     

Development of the ear, hearing capabilities and laterophysic connection in the spotfin butterflyfish (Chaetodon ocellatus)

The ontogeny of the ear, swim bladder and laterophysic connection was investigated in the spotfin butterflyfish, Chaetodon ocellatus in order to determine how the development of the laterophysic connection (a Chaetodon synapomorphy) is correlated with ontogenetic changes in the hearing capabilities in these abundant and ecologically important coral reef fishes. Histological and cleared and stained material revealed that the medial opening in the lateral line canal in the supracleithrum (which defines the laterophysic connection), an inflated physoclistous swim bladder, and the three otolithic organs are already present in the smallest individuals examined (7?C15?mm SL). The medial opening in the supracleithrum increases in size and the cylindrical swim bladder horns form after the loss of the head plates characteristic of the tholichthys stage, in individuals ??29?mm SL. The three sensory maculae of the ear increase in size, and the shape of the sacculus changes most dramatically with fish growth; hair cell density is highest in the utriculus. Physiological analysis of the reponse to sound pressure showed that larval and juvenile C. ocellatus had a hearing sensitivity peak at 100?C200?Hz, which was ~30?C40?dB more sensitive than that measured in larval coral reef fishes (e.g., damselfishes) that lack swim bladder horns. C. ocellatus did not show any ontogenetic changes in sensitivity to sound pressure, which may be explained by the fact that the growth of the swim bladder horns maintains the small distance between the swim bladder and ear that was established earlier during the larval stage. The timing of the development of the swim bladder horns suggests that if the laterophysic connection has a sensory acoustic function, its presence in individuals >29?mm SL suggests that its role is limited to post-settlement, reef-based behaviors.     

Left hemispheric dominance during auditory processing in a noisy environment

Background  

In daily life, we are exposed to different sound inputs simultaneously. During neural encoding in the auditory pathway, neural activities elicited by these different sounds interact with each other. In the present study, we investigated neural interactions elicited by masker and amplitude-modulated test stimulus in primary and non-primary human auditory cortex during ipsi-lateral and contra-lateral masking by means of magnetoencephalography (MEG).     

Auditory information processing in stridulating grasshoppers: tympanic membrane vibrations and neurophysiology

During stridulation in the gomphocerine grasshopper Omocestus viridulus the leg movements, sound pattern and either summed auditory nerve activity or single interneuron activity were recorded. Simultaneous laser interferometric and vibrometric measurements of the displacement and velocity of the tympanic membrane were performed at the pyriform vesicle (d-receptor group). Slow displacements of the tympanic membrane occur in phase with the ventilatory and stridulatory rhythm and reach 10 m_peak-peak and 1–3 m_peak-peak in amplitude, respectively. Additionally, the tympanic membrane oscillates maximally in the range 5–10 kHz. These high-frequency oscillations are due to sound production and motor activity and correspond in amplitude to oscillations evoked by sound pressures of 90-dB SPL. They activate the auditory receptors during most of the stridulatory cycle even during mute stridulation. Only at the lower reversal point of the leg movement are membrane vibrations and receptor activity at a minimum. As a consequence the response of receptors and interneurons to auditory stimuli are generally impaired and an auditory response of receptors and interneurons can be elicited only during a short period at the lower reversal point. Although in this phase of the stridulatory cycle auditory sensitivity is present, males do not show phonotactic responses towards female songs during ongoing own stridulation.     

Auditory temporal resolution and evoked responses to pulsed sounds for the Yangtze finless porpoises (<Emphasis Type="Italic">Neophocaena phocaenoides asiaeorientalis</Emphasis>)

Temporal cues are important for some forms of auditory processing, such as echolocation. Among odontocetes (toothed whales, dolphins, and porpoises), it has been suggested that porpoises may have temporal processing abilities which differ from other odontocetes because of their relatively narrow auditory filters and longer duration echolocation signals. This study examined auditory temporal resolution in two Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis) using auditory evoked potentials (AEPs) to measure: (a) rate following responses and modulation rate transfer function for 100 kHz centered pulse sounds and (b) hearing thresholds and response amplitudes generated by individual pulses of different durations. The animals followed pulses well at modulation rates up to 1,250 Hz, after which response amplitudes declined until extinguished beyond 2,500 Hz. The subjects had significantly better hearing thresholds for longer, narrower-band pulses similar to porpoise echolocation signals compared to brief, broadband sounds resembling dolphin clicks. Results indicate that the Yangtze finless porpoise follows individual acoustic signals at rates similar to other odontocetes tested. Relatively good sensitivity for longer duration, narrow-band signals suggests that finless porpoise hearing is well suited to detect their unique echolocation signals.     

Sex-specific asymmetries in communication sound perception are not related to hand preference in an early primate

Background  

Left hemispheric dominance of language processing and handedness, previously thought to be unique to humans, is currently under debate. To gain an insight into the origin of lateralization in primates, we have studied gray mouse lemurs, suggested to represent the most ancestral primate condition. We explored potential functional asymmetries on the behavioral level by applying a combined handedness and auditory perception task. For testing handedness, we used a forced food-grasping task. For testing auditory perception, we adapted the head turn paradigm, originally established for exploring hemispheric specializations in conspecific sound processing in Old World monkeys, and exposed 38 subjects to control sounds and conspecific communication sounds of positive and negative emotional valence.     

Effects of Temperature on Auditory Sensitivity in Eurythermal Fishes: Common Carp Cyprinus carpio (Family Cyprinidae) versus Wels Catfish Silurus glanis (Family Siluridae)

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.