David G. Zeddies

Development of the acoustically evoked behavioral response in zebrafish to pure tones

SUMMARY Zebrafish (Danio rerio) were placed in small wells that could be driven vertically with a series of calibrated sinusoids. Video images of the fish were obtained and analyzed to determine the levels and frequencies at which the fish responded to the stimulus tones. It was found that fish 4 days post fertilization (dpf) did not respond to the stimulus tones, whereas fish 5 dpf to adult did respond. It was further found that the stimulus thresholds and frequency bandwidth to which the fish responded did not change from 5 dpf to adult; indicating that the otolithic organ adaptations for high-frequency hearing are already present in larval fish. Deflating the swimbladders in adult fish eliminated their response, which is consistent with sensing sound pressure. Deflating the swimbladder in larval fish did not affect their thresholds, which is consistent with sensing the particle motion of the fluid directly. Because adult fish with Weberian ossicles have a greater input to the inner ear for a given sound pressure level (SPL), the finding that the adult and larval fish respond at the same SPL with intact swimbladders suggests that the acoustic startle response threshold is adjusted as the fish develop in order to maintain appropriate reactions to relevant stimuli.

Auditory sensitivity of larval zebrafish (Danio rerio) measured using a behavioral prepulse inhibition assay.

SUMMARY Zebrafish (Danio rerio) have become a valuable model for investigating the molecular genetics and development of the inner ear in vertebrates. In this study, we employed a prepulse inhibition (PPI) paradigm to assess hearing in larval wild-type (AB) zebrafish during early development at 5–6 days post-fertilization (d.p.f.). We measured the PPI of the acoustic startle response in zebrafish using a 1-dimensional shaker that simulated the particle motion component of sound along the fishs dorsoventral axis. The thresholds to startle-inducing stimuli were determined in 5–6 d.p.f. zebrafish, and their hearing sensitivity was then characterized using the thresholds of prepulse tone stimuli (90–1200 Hz) that inhibited the acoustic startle response to a reliable startle stimulus (820 Hz at 20 dB re. 1 m s−2). Hearing thresholds were defined as the minimum prepulse tone level required to significantly reduce the startle response probability compared with the baseline (no-prepulse) condition. Larval zebrafish showed greatest auditory sensitivity from 90 to 310 Hz with corresponding mean thresholds of −19 to −10 dB re. 1 m s−2, respectively. Hearing thresholds of prepulse tones were considerably lower than previously predicted by startle response assays. The PPI assay was also used to investigate the relative contribution of the lateral line to the detection of acoustic stimuli. After aminoglycoside-induced neuromast hair-cell ablation, we found no difference in PPI thresholds between treated and control fish. We propose that this PPI assay can be used to screen for novel zebrafish hearing mutants and to investigate the ontogeny of hearing in zebrafish and other fishes.

Local acoustic particle motion guides sound-source localization behavior in the plainfin midshipman fish, Porichthys notatus

SUMMARY Sound-source localization behavior was studied in the plainfin midshipman fish (Porichthys notatus) by making use of the naturally occurring phonotaxis response of gravid females to playback of the males advertisement call. The observations took place outdoors in a circular concrete tank. A dipole sound projector was placed at the center of the tank and an 80–90 Hz tone (the approximate fundamental frequency to the males advertisement call) was broadcast to gravid females that were released from alternative sites approximately 100 cm from the source. The phonotaxic responses of females to the source were recorded, analyzed and compared with the sound field. One release site was approximately along the vibratory axis of the dipole source, and the other was approximately orthogonal to the vibratory axis. The sound field in the tank was fully characterized through measurements of the sound pressure field using hydrophones and acoustic particle motion using an accelerometer. These measurements confirmed that the sound field was a nearly ideal dipole. When released along the dipole vibratory axis, the responding female fish took essentially straight paths to the source. However, when released approximately 90 deg to the sources vibratory axis, the responding females took highly curved paths to the source that were approximately in line with the local particle motion axes. These results indicate that the acoustic cues used by fish during sound-source localization include the axes of particle motion of the local sound field.

Use of the swim bladder and lateral line in near-field sound source localization by fish

We investigated the roles of the swim bladder and the lateral line system in sound localization behavior by the plainfin midshipman fish (Porichthys notatus). Reproductive female midshipman underwent either surgical deflation of the swim bladder or cryoablation of the lateral line and were then tested in a monopolar sound source localization task. Fish with nominally ‘deflated’ swim bladders performed similar to sham-deflated controls; however, post-experiment evaluation of swim bladder deflation revealed that a majority of ‘deflated’ fish (88%, seven of the eight fish) that exhibited positive phonotaxis had partially inflated swim bladders. In total, 95% (21/22) of fish that localized the source had at least partially inflated swim bladders, indicating that pressure reception is likely required for sound source localization. In lateral line experiments, no difference was observed in the proportion of females exhibiting positive phonotaxis with ablated (37%) versus sham-ablated (47%) lateral line systems. These data suggest that the lateral line system is likely not required for sound source localization, although this system may be important for fine-tuning the approach to the sound source. We found that midshipman can solve the 180 deg ambiguity of source direction in the shallow water of our test tank, which is similar to their nesting environment. We also found that the potential directional cues (phase relationship between pressure and particle motion) in shallow water differs from a theoretical free-field. Therefore, the general question of how fish use acoustic pressure cues to solve the 180 deg ambiguity of source direction from the particle motion vector remains unresolved.

Seasonal plasticity of auditory saccular sensitivity in “sneaker” type II male plainfin midshipman fish, Porichthys notatus

Adult female and nesting (type I) male midshipman fish (Porichthys notatus) exhibit an adaptive form of auditory plasticity for the enhanced detection of social acoustic signals. Whether this adaptive plasticity also occurs in “sneaker” type II males is unknown. Here, we characterize auditory-evoked potentials recorded from hair cells in the saccule of reproductive and non-reproductive “sneaker” type II male midshipman to determine whether this sexual phenotype exhibits seasonal, reproductive state-dependent changes in auditory sensitivity and frequency response to behaviorally relevant auditory stimuli. Saccular potentials were recorded from the middle and caudal region of the saccule while sound was presented via an underwater speaker. Our results indicate saccular hair cells from reproductive type II males had thresholds based on measures of sound pressure and acceleration (re. 1xa0µPa and 1xa0ms−2, respectively) that were ~8–21xa0dB lower than non-reproductive type II males across a broad range of frequencies, which include the dominant higher frequencies in type I male vocalizations. This increase in type II auditory sensitivity may potentially facilitate eavesdropping by sneaker males and their assessment of vocal type I males for the selection of cuckoldry sites during the breeding season.

Effects of Exposure to the Sound from Seismic Airguns on Pallid Sturgeon and Paddlefish

This study examined the effects of exposure to a single acoustic pulse from a seismic airgun array on caged endangered pallid sturgeon (Scaphirhynchus albus) and on paddlefish (Polyodon spathula) in Lake Sakakawea (North Dakota, USA). The experiment was designed to detect the onset of physiological responses including minor to mortal injuries. Experimental fish were held in cages as close as 1 to 3 m from the guns where peak negative sound pressure levels (Peak- SPL) reached 231 dB re 1 μPa (205 dB re 1 μPa2·s sound exposure level [SEL]). Additional cages were placed at greater distances in an attempt to develop a dose-response relationship. Treatment and control fish were then monitored for seven days, euthanized, and necropsied to determine injuries. Necropsy results indicated that the probability of delayed mortality associated with pulse pressure following the seven day monitoring period was the same for exposed and control fish of both species. Exposure to a single pulse from a small air gun array (10,160 cm3) was not lethal for pallid sturgeon and paddlefish. However, the risks from exposure to multiple sounds and to sound exposure levels that exceed those reported here remain to be examined.

Evaluation of Three Sensor Types for Particle Motion Measurement

All fish sense acoustic particle motion; some species also sense pressure. Concern over the effects of anthropogenic sounds is increasing the need to monitor acoustic particle motion. Particle motion can be measured directly using vector sensors or calculated from pressure gradients. This article compares three devices that measure particle motion: a three-axis accelerometer, a three-axis velocity sensor, and two 4-element hydrophone arrays. A series of sounds (constant-wave tones, white noise, and Ricker wavelets) were played from a fixed-position projector. The particle motion of sounds from imploding light bulbs was also measured.

Sound Exposure Guidelines

Chapters cannot be read stand-alone. Please see complete SpringerBrief at: http://link.springer.com/book/10.1007/978-3-319-06659-2.

Effects of Seismic Air Guns on Pallid Sturgeon and Paddlefish

Pallid sturgeon and paddlefish were placed at different distances from a seismic air gun array to determine the potential effects on mortality and nonauditory body tissues from the sound from a single shot. Fish were held 7 days postexposure and then necropsied. No fish died immediately after sound exposure or over the postexposure period. Statistical analysis of injuries showed no differences between the experimental and control animals in either type or severity of injuries. There was also no difference in injuries between fish exposed closest to the source compared with those exposed furthest from the source.

Effects of Sound Exposure

Chapters cannot be read stand-alone. Please see complete SpringerBrief at: http://link.springer.com/book/10.1007/978-3-319-06659-2.