243
because the hair cells are oriented in only one direction and the evoked potential
occurs at the stimulus frequency (de Vries and Bleeker 1949 ; Tasaki et al. 1954 ).
The magnitude of the saccular potentials in the Hawaiian sergeant fi sh were generally lower than and did not have the dynamic range of those observed in the midshipman and Lusitanian toadfi sh measured with the identical experimental setup
(Sisneros 2007 ; Alderks and Sisneros 2011 ; Vasconcelos et al. 2011 ). This difference could be due to several factors including electrode placement in the saccule
(either distance between recording electrode and hair cells, or position of electrode
in regions with hair cells oriented off the vertical stimulation axis), especially since
the saccule in A. abdominalis is located deep within the otic capsule beneath the
medulla. This location makes it diffi cult to position electrodes in this area compared
to the more easily accessible and laterally positioned saccule in batrachoidid fi shes.
Alternatively, the Hawaiian sergeant fi sh saccule may just be less sensitive than the
midshipman to stimuli along the dorso-ventral axis. Nevertheless, the tuning curves
obtained by saccular potential recordings in the Hawaiian sergeant fi sh are within
the range of thresholds obtained by the AEP technique in this species and in the
congener A. saxatilis (Egner and Mann 2005 ). Recordings from individual endorgans like the saccule in fi shes provide important information about the response
properties of hair cells, which are the fi rst processing level of the auditory system.
These types of recordings are also valuable for comparisons to recordings done at
subsequent processing levels. For example, saccular (and lagenar and utricular)
recordings can be used to evaluate whether changes in auditory sensitivity due to
circulating hormones or noise exposure occur at the level of the macula and hair
cells, or elsewhere along the auditory pathway.
Our fi ner low-frequency resolution tuning curve generated for the Hawaiian
sergeant fi sh by AEP is similar to that previously determined using fewer test frequencies (Maruska et al. 2007 ). The additional frequencies, however, further highlight that this species is most sensitive to tonal stimuli of ≤200 Hz, with slightly
lower sensitivity but with similar thresholds across the range of 200–285 Hz, and
then with a steady drop in auditory sensitivity from 300 to 800 Hz. The low thresholds measured across this frequency range overlaps the dominant spectral energy
found in all of the natural agonistic and courtship sounds produced by this species
(<80–400 Hz) (Maruska et al. 2007 ), illustrating a match between hearing ability
and sound production for communication. Low frequency acoustic information is
also likely important for all fi shes to survey complex “soundscapes” for mediating
other non-communicative behaviors such as prey detection, predator avoidance,
and assessment of ambient noise and environmental disturbances (Fay 2009 ). This
low- pass frequency hearing is similar to most other fi shes that do not have accessory auditory specializations (e.g., midshipman and toadfi sh) but instead rely on the
otolithic endorgans that detect acoustic particle motion by acting as inertial accelerometers (Fay and Edds-Walton 1997 ; Sisneros 2007 ). Fishes that do possess adaptations to detect the pressure component of sound stimuli, on the other hand, typically
have enhanced high-frequency hearing abilities (e.g., goldfi sh, mormyrids, clupeids, labyrinth fi shes). However, even these species that detect high frequencies
(≥800 Hz) have some saccular primary afferent and central neurons tuned to low
Comparison of Electrophysiological Auditory Measures in Fishes
because the hair cells are oriented in only one direction and the evoked potential
occurs at the stimulus frequency (de Vries and Bleeker 1949 ; Tasaki et al. 1954 ).
The magnitude of the saccular potentials in the Hawaiian sergeant fi sh were generally lower than and did not have the dynamic range of those observed in the midshipman and Lusitanian toadfi sh measured with the identical experimental setup
(Sisneros 2007 ; Alderks and Sisneros 2011 ; Vasconcelos et al. 2011 ). This difference could be due to several factors including electrode placement in the saccule
(either distance between recording electrode and hair cells, or position of electrode
in regions with hair cells oriented off the vertical stimulation axis), especially since
the saccule in A. abdominalis is located deep within the otic capsule beneath the
medulla. This location makes it diffi cult to position electrodes in this area compared
to the more easily accessible and laterally positioned saccule in batrachoidid fi shes.
Alternatively, the Hawaiian sergeant fi sh saccule may just be less sensitive than the
midshipman to stimuli along the dorso-ventral axis. Nevertheless, the tuning curves
obtained by saccular potential recordings in the Hawaiian sergeant fi sh are within
the range of thresholds obtained by the AEP technique in this species and in the
congener A. saxatilis (Egner and Mann 2005 ). Recordings from individual endorgans like the saccule in fi shes provide important information about the response
properties of hair cells, which are the fi rst processing level of the auditory system.
These types of recordings are also valuable for comparisons to recordings done at
subsequent processing levels. For example, saccular (and lagenar and utricular)
recordings can be used to evaluate whether changes in auditory sensitivity due to
circulating hormones or noise exposure occur at the level of the macula and hair
cells, or elsewhere along the auditory pathway.
Our fi ner low-frequency resolution tuning curve generated for the Hawaiian
sergeant fi sh by AEP is similar to that previously determined using fewer test frequencies (Maruska et al. 2007 ). The additional frequencies, however, further highlight that this species is most sensitive to tonal stimuli of ≤200 Hz, with slightly
lower sensitivity but with similar thresholds across the range of 200–285 Hz, and
then with a steady drop in auditory sensitivity from 300 to 800 Hz. The low thresholds measured across this frequency range overlaps the dominant spectral energy
found in all of the natural agonistic and courtship sounds produced by this species
(<80–400 Hz) (Maruska et al. 2007 ), illustrating a match between hearing ability
and sound production for communication. Low frequency acoustic information is
also likely important for all fi shes to survey complex “soundscapes” for mediating
other non-communicative behaviors such as prey detection, predator avoidance,
and assessment of ambient noise and environmental disturbances (Fay 2009 ). This
low- pass frequency hearing is similar to most other fi shes that do not have accessory auditory specializations (e.g., midshipman and toadfi sh) but instead rely on the
otolithic endorgans that detect acoustic particle motion by acting as inertial accelerometers (Fay and Edds-Walton 1997 ; Sisneros 2007 ). Fishes that do possess adaptations to detect the pressure component of sound stimuli, on the other hand, typically
have enhanced high-frequency hearing abilities (e.g., goldfi sh, mormyrids, clupeids, labyrinth fi shes). However, even these species that detect high frequencies
(≥800 Hz) have some saccular primary afferent and central neurons tuned to low
Comparison of Electrophysiological Auditory Measures in Fishes