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

Natural soundscapes of lowland river habitats and the potential threat of urban noise pollution to migratory fish

Migratory fish populations have experienced great declines, and considerable effort have been put into reducing stressors, such as chemical pollution and physical barriers. However, the importance of natural sounds as an information source and potential problems caused by noise pollution remain largely unexplored. The spatial distribution of sound sources and variation in propagation characteristics could provide migratory fish with acoustic cues about habitat suitability, predator presence, food availability and conspecific presence. We here investigated the relationship between natural soundscapes and local river conditions and we explored the presence of human-related sounds in these natural soundscapes. We found that 1a) natural river sound profiles vary with river scale and cross-sectional position, and that 1b) depth, width, water velocity, and distance from shore were all significant factors in explaining local soundscape variation. We also found 2a) audible human activities in almost all our underwater recordings and urban and suburban river parts had elevated sound levels relative to rural river parts. Furthermore, 2b) daytime levels were louder than night time sound levels, and bridges and nearby road traffic were much more prominent with diurnal and weekly patterns of anthropogenic noise in the river systems. We believe our data show high potential for natural soundscapes of low-land river habitat to serve as important environmental cues to migratory fish. However, anthropogenic noise may be particularly problematic due to the omnipresence, and relatively loud levels relative to the modest dynamic range of the natural sound sources, in these slow-flowing freshwater systems.

Investigation on the contribution of swim bladder to hearing in crucian carp (Carassius carassius)

The swim bladder in some teleost fish functions to transfer the sound energy of acoustic stimuli to the inner ears. This study uses the auditory evoked potential tests, micro-computed tomography scanning, reconstruction, and numerical modeling to assess the contribution of the swim bladder to hearing in crucian carp (Carassius carassius). The auditory evoked potential results show that, at the tested frequency range, the audiogram of fish with an intact swim bladder linearly increases, ranging from 100 to 600 Hz. Over this frequency, the sound pressure thresholds have a local lowest value at 800 Hz. The mean auditory threshold of fish with an intact swim bladder is lower than that of fish with a deflated swim bladder by 0.8-20.7 dB. Furthermore, numerical simulations show that the received pressure of the intact swim bladders occurs at a mean peak frequency of 826 ± 13.6 Hz, and no peak response is found in the deflated swim bladders. The increased sensitivity of reception in sound pressure and acceleration are 34.4 dB re 1 μPa and 40.3 dB re 1 m·s-2 at the natural frequency of swim bladder, respectively. Both electrophysiological measurement and numerical simulation results show that the swim bladder can potentially extend hearing bandwidth and further enhance auditory sensitivity in C. carassius.

Finite element modelling of sound transmission in the Weberian apparatus of zebrafish (Danio rerio)

Zebrafish, an essential vertebrate model, has greatly expanded our understanding of hearing. However, one area that remains unexplored is the biomechanics of the Weberian apparatus, crucial for sound conduction and perception. Using micro-computed tomography (μCT) bioimaging, we created three-dimensional finite element models of the zebrafish Weberian ossicles. These models ranged from the exact size to scaled isometric versions with constrained geometry (1 to 10 mm in ossicular chain length). Harmonic finite element analysis of all 11 models revealed that the resonance frequency of the zebrafish's Weberian ossicular chain is approximately 900 Hz, matching their optimal hearing range. Interestingly, resonance frequency negatively correlated with size, while the ratio of peak displacement and difference of resonance frequency between tripus and scaphium remained constant. This suggests the transmission efficiency of the ossicular chain and the homogeneity of resonance frequency at both ends of the chain are not size-dependent. We conclude that the Weberian apparatus's resonance frequency can explain zebrafish's best hearing frequency, and their biomechanical characteristics are not influenced by isometric ontogeny. As the first biomechanical modelling of atympanic ear and among the few non-human ear modelling, this study provides a methodological framework for further investigations into hearing mechanisms and the hearing evolution of vertebrates.

Hearing in catfishes: 200 years of research

Ernst Weber stated in 1819, based on dissections, that the swimbladder in the European wels (Silurus glanis, Siluridae) and related cyprinids serves as an eardrum and that the ossicles connecting it to the inner ear function as hearing ossicles similar to mammals. In the early 20th century, K. von Frisch showed experimentally that catfishes and cyprinids (otophysines) indeed hear excellently compared to fish taxa lacking auxiliary hearing structures (ossicles, eardrums). Knowledge on hearing in catfishes progressed in particular in the 21st century. Currently, hearing abilities (audiograms) are known in 28 species out of 13 families. Recent ontogenetic and comparative studies revealed that the ability to detect sounds of low-level and high frequencies (4-6 kHz) depends on the development of Weberian ossicles. Species with a higher number of ossicles and larger bladders hear better at higher frequencies (>1 kHz). Hearing sensitivities are furthermore affected by ecological factors. Rising temperatures increase, whereas various noise regimes decrease hearing. Exposure to high-noise levels (>150 dB) for hours result in temporary thresholds shifts (TTS) and recovery of hearing after several days. Low-noise levels reduce hearing abilities due to masking without a TTS. Furthermore, auditory evoked potential (AEP) experiments reveal that the temporal patterns of fish-produced pulsed stridulation and drumming sounds are represented in their auditory pathways, indicating that catfishes are able to extract important information for acoustic communication. Further research should concentrate on inner ears to determine whether the diversity in swimbladders and ossicles is paralleled in the inner ear fine structure.

The Sound World of Zebrafish: A Critical Review of Hearing Assessment

Zebrafish, like all fish species, use sound to learn about their environment. Thus, human-generated (anthropogenic) sound added to the environment has the potential to disrupt the detection of biologically relevant sounds, alter behavior, impact fitness, and produce stress and other effects that can alter the well-being of animals. This review considers the bioacoustics of zebrafish in the laboratory with two goals. First, we discuss zebrafish hearing and the problems and issues that must be considered in any studies to get a clear understanding of hearing capabilities. Second, we focus on the potential effects of sounds in the tank environment and its impact on zebrafish physiology and health. To do this, we discuss underwater acoustics and the very specialized acoustics of fish tanks, in which zebrafish live and are studied. We consider what is known about zebrafish hearing and what is known about the potential impacts of tank acoustics on zebrafish and their well-being. We conclude with suggestions regarding the major gaps in what is known about zebrafish hearing as well as questions that must be explored to better understand how well zebrafish tolerate and deal with the acoustic world they live in within laboratories.

Sensorimotor Transformations in the Zebrafish Auditory System

Organisms use their sensory systems to acquire information from their environment and integrate this information to produce relevant behaviors. Nevertheless, how sensory information is converted into adequate motor patterns in the brain remains an open question. Here, we addressed this question using two-photon and light-sheet calcium imaging in intact, behaving zebrafish larvae. We monitored neural activity elicited by auditory stimuli while simultaneously recording tail movements. We observed a spatial organization of neural activity according to four different response profiles (frequency tuning curves), suggesting a low-dimensional representation of frequency information, maintained throughout the development of the larvae. Low frequencies (150-450 Hz) were locally processed in the hindbrain and elicited motor behaviors. In contrast, higher frequencies (900-1,000 Hz) rarely induced motor behaviors and were also represented in the midbrain. Finally, we found that the sensorimotor transformations in the zebrafish auditory system are a continuous and gradual process that involves the temporal integration of the sensory response in order to generate a motor behavior.

Hearing capacities and morphology of the auditory system in Serrasalmidae (Teleostei: Otophysi)

Like all otophysan fishes, serrasalmids (piranhas and relatives) possess a Weberian apparatus that improves their hearing capacities. We compared the hearing abilities among eight species of serrasalmids having different life-history traits: herbivorous vs. carnivorous and vocal vs. mute species. We also made 3D reconstructions of the auditory system to detect potential morphological variations associated with hearing ability. The hearing structures were similar in overall shape and position. All the species hear in the same frequency range and only slight differences were found in hearing thresholds. The eight species have their range of best hearing in the lower frequencies (50–900 Hz). In vocal serrasalmids, the range of best hearing covers the frequency spectrum of their sounds. However, the broad overlap in hearing thresholds among species having different life-history traits (herbivorous vs. carnivorous and vocal vs. non-vocal species) suggests that hearing ability is likely not related to the capacity to emit acoustic signals or to the diet, i.e. the ability to detect sounds is not associated with a given kind of food. The inner ear appears to be highly conservative in this group suggesting that it is shaped by phylogenetic history or by other kinds of constraints such as predator avoidance.

Behavioral methods for the functional assessment of hair cells in zebrafish

Zebrafish is an emerging animal model for studies on auditory system. This model presents high comparability with humans, good accessibility to the hearing organ, and high throughput capacity. To better utilize this animal model, methodologies need to be used to quantify the hearing function of the zebrafish. Zebrafish displays a series of innate and robust behavior related to its auditory function. Here, we reviewed the advantage of using zebrafish in auditory research and then introduced three behavioral tests, as follows: the startle response, the vestibular-ocular reflex, and rheotaxis. These tests are discussed in terms of their physiological characteristics, up-to-date technical development, and apparatus description. Test limitation and areas to improve are also introduced. Finally, we revealed the feasibility of these applications in zebrafish behavioral assessment and their potential in the high-throughput screening on hearing-related genes and drugs.

Causes and Consequences of Sensory Hair Cell Damage and Recovery in Fishes

Sensory hair cells are the mechanotransductive receptors that detect gravity, sound, and vibration in all vertebrates. Damage to these sensitive receptors often results in deficits in vestibular function and hearing. There are currently two main reasons for studying the process of hair cell loss in fishes. First, fishes, like other non-mammalian vertebrates, have the ability to regenerate hair cells that have been damaged or lost via exposure to ototoxic chemicals or acoustic overstimulation. Thus, they are used as a biomedical model to understand the process of hair cell death and regeneration and find therapeutics that treat or prevent human hearing loss. Secondly, scientists and governmental natural resource managers are concerned about the potential effects of intense anthropogenic sounds on aquatic organisms, including fishes. Dr. Arthur N. Popper and his students, postdocs and research associates have performed pioneering experiments in both of these lines of fish hearing research. This review will discuss the current knowledge regarding the causes and consequences of both lateral line and inner ear hair cell damage in teleost fishes.

Development of Structure and Sensitivity of the Fish Inner Ear

Fish represent the largest group of vertebrates and display the greatest diversity of auditory structures. However, studies addressing how the form and function of the auditory system change during development to enhance perception of the acoustic environment are rather sparse in this taxon compared to other vertebrate groups. An ontogenetic perspective of the auditory system in fishes provides a readily testable framework for understanding structure-function relationships. Additionally, studying ancestral models such as fish can convey valuable comparable information across vertebrates, as early developmental events are often evolutionary conserved. This chapter reviews the literature on the morphological development of the fish auditory system, with particular focus on the inner ear structures that evolve from an otic placode during early embryonic development and then continue to undergo differentiation and maturation in the postembryonic phase. Moreover, the chapter provides a systematic overview of how auditory sensitivity develops during ontogeny. Although most studies indicate a developmental improvement in auditory sensitivity, there is considerably species-specific variation. Lastly, the paucity of information and literature concerning the development of auditory capabilities for social communication in fishes is also discussed. Further investigation on the development of structure and function of the fish auditory system is recommended in order to obtain a deeper understanding of how ontogenetic morphological changes in the auditory pathway relate to modifications in acoustic reception, auditory processing, and the capacity to communicate acoustically.

Ontogenetic development of the auditory sensory organ in zebrafish (Danio rerio): changes in hearing sensitivity and related morphology

Zebrafish (Danio rerio) is an important model organism in hearing research. However, data on the hearing sensitivity of zebrafish vary across different reports. In the present study, the hearing sensitivity of zebrafish was examined by analysing the auditory evoked potentials (AEPs) over a range of total lengths (TLs) from 12 to 46 mm. Morphological changes in the hair cells (HCs) of the saccule (the main auditory end organ) and their synapses with primary auditory neurons were investigated. The AEPs were detected up to a much higher frequency limit (12 kHz) than previously reported. No significant difference in the frequency response range was observed across the TL range examined. However, the AEP thresholds demonstrated both developmental improvement and age-related loss of hearing sensitivity. The changes in hearing sensitivity were roughly consistent with the morphological changes in the saccule including (1) the number and density of HCs, (2) the organization of stereocilia, and (3) the quantity of a main ribbon protein, Ribeye b. The results of this study established a clear baseline for the hearing ability of zebrafish and revealed that the changes in the saccule contribute to the observed changes in TL (age)-related hearing sensitivity.

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

Vocal differentiation is widely documented in birds and mammals but has been poorly investigated in other vertebrates, including fish, which represent the oldest extant vertebrate group. Neural circuitry controlling vocal behaviour is thought to have evolved from conserved brain areas that originated in fish, making this taxon key to understanding the evolution and development of the vertebrate vocal-auditory systems. This study examines ontogenetic changes in the vocal repertoire and whether vocal differentiation parallels auditory development in the Lusitanian toadfish Halobatrachus didactylus (Batrachoididae). This species exhibits a complex acoustic repertoire and is vocally active during early development. Vocalisations were recorded during social interactions for four size groups (fry: <2 cm; small juveniles: 2–4 cm; large juveniles: 5–7 cm; adults >25 cm, standard length). Auditory sensitivity of juveniles and adults was determined based on evoked potentials recorded from the inner ear saccule in response to pure tones of 75–945 Hz. We show an ontogenetic increment in the vocal repertoire from simple broadband-pulsed ‘grunts’ that later differentiate into four distinct vocalisations, including low-frequency amplitude-modulated ‘boatwhistles’. Whereas fry emitted mostly single grunts, large juveniles exhibited vocalisations similar to the adult vocal repertoire. Saccular sensitivity revealed a three-fold enhancement at most frequencies tested from small to large juveniles; however, large juveniles were similar in sensitivity to adults. We provide the first clear evidence of ontogenetic vocal differentiation in fish, as previously described for higher vertebrates. Our results suggest a parallel development between the vocal motor pathway and the peripheral auditory system for acoustic social communication in fish.

The auditory roles of the gas bladder and suprabranchial chamber in walking catfish (Clarias batrachus)

Background

The enhanced auditory abilities of certain fish are dependent on specialized hearing structures. Several gas-holding structures, including the suprabranchial chamber, otic gas bladder, and Weberian apparatus-linked gas bladder, have been demonstrated to improve the hearing ability of fish. The walking catfish (Clarias batrachus), a benthic species, is unique in that it has both a suprabranchial chamber (SC) and a Weberian apparatus-linked, encapsulated gas bladder (WGB). This study aimed to investigate the respective roles of these two structures in contributing to the overall hearing ability of walking catfish.

Results

The auditory evoked potentials method was used to measure hearing thresholds in intact fish and fish with a deflated WGB and/or SC. Gas removal from the WGB increased auditory thresholds at all frequencies tested (0.4 to 5.0 kHz), whereas injection of water into the SC shifted the threshold only at frequencies below 3.0 kHz. However, such a correlation was not observed for the SC at 4.0 and 5.0 kHz.

Conclusions

The findings indicated that both the encapsulated WGB and the SC had an accessory auditory role. However, WGB enhanced hearing abilities in the whole frequency range, whereas SC did not.

Early development of hearing in zebrafish

The zebrafish (Danio rerio) has become a valuable vertebrate model for human hearing and balance disorders because it combines powerful genetics, excellent embryology, and exceptional in vivo visualization in one organism. In this study, we investigated auditory function of zebrafish at early developmental stages using the microphonic potential method. This is the first study to report ontogeny of response of hair cells in any fish during the first week post fertilization. The right ear of each zebrafish embedded in agarose was linearly stimulated with a glass probe that was driven by a calibrated piezoelectric actuator. Using beveled micropipettes filled with standard fish saline, extracellular microphonic potentials were recorded from hair cells in the inner ear of zebrafish embryos or larvae in response to 20, 50, 100, and 200-Hz stimulation. Saccular hair cells expressing green fluorescent protein of the transgenic zebrafish from 2 to 7 days post fertilization (dpf) were visualized and quantified using confocal microscopy. The otic vesicles' areas, otoliths' areas, and saccular hair cell count and density increased linearly with age and standard body length. Microphonic responses increased monotonically with stimulus intensity, stimulus frequency, and age of zebrafish. Microphonic threshold at 200 Hz gradually decreased with zebrafish age. The increases in microphonic response and sensitivity correlate with the increases in number and density of hair cells in the saccule. These results enhance our knowledge of early development of auditory function in zebrafish and provide the control data that can be used to evaluate hearing of young zebrafish morphants or mutants.

Auditory evoked potential audiometry in fish

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.

The African cichlid fish Astatotilapia burtoni uses acoustic communication for reproduction: sound production, hearing, and behavioral significance

Sexual reproduction in all animals depends on effective communication between signalers and receivers. Many fish species, especially the African cichlids, are well known for their bright coloration and the importance of visual signaling during courtship and mate choice, but little is known about what role acoustic communication plays during mating and how it contributes to sexual selection in this phenotypically diverse group of vertebrates. Here we examined acoustic communication during reproduction in the social cichlid fish, Astatotilapia burtoni. We characterized the sounds and associated behaviors produced by dominant males during courtship, tested for differences in hearing ability associated with female reproductive state and male social status, and then tested the hypothesis that female mate preference is influenced by male sound production. We show that dominant males produce intentional courtship sounds in close proximity to females, and that sounds are spectrally similar to their hearing abilities. Females were 2–5-fold more sensitive to low frequency sounds in the spectral range of male courtship sounds when they were sexually-receptive compared to during the mouthbrooding parental phase. Hearing thresholds were also negatively correlated with circulating sex-steroid levels in females but positively correlated in males, suggesting a potential role for steroids in reproductive-state auditory plasticity. Behavioral experiments showed that receptive females preferred to affiliate with males that were associated with playback of courtship sounds compared to noise controls, indicating that acoustic information is likely important for female mate choice. These data show for the first time in a Tanganyikan cichlid that acoustic communication is important during reproduction as part of a multimodal signaling repertoire, and that perception of auditory information changes depending on the animal's internal physiological state. Our results highlight the importance of examining non-visual sensory modalities as potential substrates for sexual selection contributing to the incredible phenotypic diversity of African cichlid fishes.