302
Alternatively, electrophysiology techniques have also been used, namely multiunit
recordings from the auditory cranial nerve (Corwin 1983 ; Sisneros and Bass 2005 )
or measurement of evoked responses from populations of saccular hair cells
(Alderks and Sisneros 2011 ), to characterize auditory sensitivity during ontogeny.
However, the most common electrophysiology technique used to determine
hearing sensitivity in fi sh during ontogeny is the AEP recording technique, which
was introduced and adapted for fi sh by Kenyon et al. ( 1998 ). This technique is used
to measure the overall neural auditory responses evoked by auditory stimuli and
consists of the summation of evoked fi eld potentials from central brain regions,
auditory nerve, and otolithic end organs over many presentations (for an extensive
review of the use of the AEP technique in fi sh hearing, see Ladich and Fay 2013 ).
The AEP technique has become a useful tool to assess the ontogenetic development
of hearing in various marine and freshwater fi shes.
In general, auditory thresholds of fi shes have largely been characterized in terms
of sound pressure, but it is now generally accepted that all fi sh species are capable
of sensing particle motion via their otolithic end organs and only some fi sh species
possess accessory hearing specializations that allow them to detect sound pressure.
Most of the previous studies presented auditory threshold data in terms of sound
pressure largely due to technical constraints, namely due to the diffi culty of measuring particle motion directly and the commercial unavailability of neutrally buoyant
underwater accelerometers. In addition, the reporting of auditory sensitivity in
terms of sound pressure was a convenient mean of comparison with the sound spectra of conspecifi c vocalizations, which is typically characterized in terms of sound
pressure.
Table 1 provides a systematic overview of the various fi sh species in which auditory sensitivity has been examined during ontogeny as well as the recordings techniques used in each study. The data in Table 1 reveals taxon-specifi c results, with
most fi sh species exhibiting auditory sensitivity improvements with age/size during
ontogeny. In addition to increased auditory sensitivity, some studies also report
changes in peak frequency sensitivity and in the detectable frequency range or
detection bandwidth.
3.1.1 Chondrichthyes (Cartilaginous Fishes)
Rajiformes
The fi rst study to report changes in auditory sensitivity during development in fi sh
was conducted by Corwin ( 1983 ) in the thornback skate Raja clavata
(Chondrichthyes, Rajidae). By means of multiunit in vitro recordings of the macula
neglecta (nonotolithic auditory end organ of the inner ear), the author showed a 500fold increase in auditory sensitivity with age/size in skates from 21 to 91 cm total
length (TL). This increase in auditory sensitivity was observed across the range of
tested frequencies such that the fi lter shape of the audiogram remained similar but
R.O. Vasconcelos et al.
Alternatively, electrophysiology techniques have also been used, namely multiunit
recordings from the auditory cranial nerve (Corwin 1983 ; Sisneros and Bass 2005 )
or measurement of evoked responses from populations of saccular hair cells
(Alderks and Sisneros 2011 ), to characterize auditory sensitivity during ontogeny.
However, the most common electrophysiology technique used to determine
hearing sensitivity in fi sh during ontogeny is the AEP recording technique, which
was introduced and adapted for fi sh by Kenyon et al. ( 1998 ). This technique is used
to measure the overall neural auditory responses evoked by auditory stimuli and
consists of the summation of evoked fi eld potentials from central brain regions,
auditory nerve, and otolithic end organs over many presentations (for an extensive
review of the use of the AEP technique in fi sh hearing, see Ladich and Fay 2013 ).
The AEP technique has become a useful tool to assess the ontogenetic development
of hearing in various marine and freshwater fi shes.
In general, auditory thresholds of fi shes have largely been characterized in terms
of sound pressure, but it is now generally accepted that all fi sh species are capable
of sensing particle motion via their otolithic end organs and only some fi sh species
possess accessory hearing specializations that allow them to detect sound pressure.
Most of the previous studies presented auditory threshold data in terms of sound
pressure largely due to technical constraints, namely due to the diffi culty of measuring particle motion directly and the commercial unavailability of neutrally buoyant
underwater accelerometers. In addition, the reporting of auditory sensitivity in
terms of sound pressure was a convenient mean of comparison with the sound spectra of conspecifi c vocalizations, which is typically characterized in terms of sound
pressure.
Table 1 provides a systematic overview of the various fi sh species in which auditory sensitivity has been examined during ontogeny as well as the recordings techniques used in each study. The data in Table 1 reveals taxon-specifi c results, with
most fi sh species exhibiting auditory sensitivity improvements with age/size during
ontogeny. In addition to increased auditory sensitivity, some studies also report
changes in peak frequency sensitivity and in the detectable frequency range or
detection bandwidth.
3.1.1 Chondrichthyes (Cartilaginous Fishes)
Rajiformes
The fi rst study to report changes in auditory sensitivity during development in fi sh
was conducted by Corwin ( 1983 ) in the thornback skate Raja clavata
(Chondrichthyes, Rajidae). By means of multiunit in vitro recordings of the macula
neglecta (nonotolithic auditory end organ of the inner ear), the author showed a 500fold increase in auditory sensitivity with age/size in skates from 21 to 91 cm total
length (TL). This increase in auditory sensitivity was observed across the range of
tested frequencies such that the fi lter shape of the audiogram remained similar but
R.O. Vasconcelos et al.