337
bladder size. Holocentrids show an improved auditory sensitivity and extended frequency range with decreasing distance to the inner ears. Sciaenids revealed a similar
trend, but an improvement of hearing sensitivity due to shorter distances could not
be demonstrated unequivocally.
Catfi shes are ideal candidates for studying the infl uence of swim bladder morphology, especially regarding organ size on hearing, because their bladders are
always connected to the inner ear. The interfamilial study by Lechner and Ladich
( 2008 ) showed that swim bladder size and distance affect hearing in catfi shes. A
larger swim bladder increases sensitivity from 1 to 6 kHz, but a shorter distance
between the bladder and the inner ear (based on a shorter ossicular chain) decreases
sensitivity. This is in contrast to our expectations that shorter distances improve
hearing but agrees with the observation in all other vertebrate classes that a higher
number of ossicles improves high-frequency hearing. Mammals possess three auditory ossicles and are on average able to detect much higher frequencies than anurans,
reptiles, or birds, which have only one middle ear ossicle (Ladich 2010 ). The intrafamilial study in thorny catfi shes by Zebedin and Ladich ( 2013 ) showed that the
infl uence of bladder size on hearing cannot be generalized. The hearing abilities
cannot be predicted when differences in swim bladder size are rather small.
Cichlids, in contrast, are the ideal fi sh family for studying both the effects of size
and distance because members of this family have large or vestigial swim bladders
and some species have connections between the swim bladder and inner ears.
Schulz-Mirbach et al. ( 2013 ) demonstrated that size and the presence of connections affect hearing in cichlids, but in different ways. Size affects the detectable
frequency range and a direct connection improves hearing sensitivity.
Finally, it needs to be mentioned that differences in auditory sensitivity between
closely related species may also refl ect factors other than peripheral hearing structures. Results from different studies need to be compared with caution due to potential differences in techniques applied in measuring hearing. Moreover, studies show
that the inner ear structure may be linked to peripheral hearing structures and that
differences in otolith size, size and form of sensory fi elds (maculae), as well as orientation patterns of sensory hair cells may affect hearing in parallel to peripheral
hearing structures (Ramcharitar et al. 2006 ; Popper and Schilt 2008 ; SchulzMirbach et al. 2014 ). An interesting task for future studies will be to show if and to
what degree particular inner ear structures help improve hearing in fi shes.
Acknowledgements This review is dedicated to Arthur N. Popper and Richard R. Fay to celebrate more than 45 years of work in fi sh bioacoustics. I am grateful to have the opportunity to work
and publish with both of them. Art invited me to his lab in 1998 and 1999 and introduced me to the
fi eld of inner ear structure in fi shes, which resulted in a common paper on labyrinth fi sh ears in
2001. Subsequently we wrote a review on the parallel evolution of fi sh hearing organs. This cooperation with Art on ears resulted years later in several studies of mine with colleagues in Germany.
Dick invited me to Fallmouth and Woods Hole in 1999. He impressed me by his knowledge in
vertebrate hearing (see his 1988 book) and his interests in all fi elds and techniques including the
auditory evoked potential (AEP) technique (which he never used). Our common “AEP” interest
resulted in 2013 in a review on the auditory evoked potential audiometry in fi shes in which we
compared behavioral to AEP data and summarized all studies published within the last 15 years.
Peripheral Hearing Structures in Fishes: Diversity and Sensitivity…
bladder size. Holocentrids show an improved auditory sensitivity and extended frequency range with decreasing distance to the inner ears. Sciaenids revealed a similar
trend, but an improvement of hearing sensitivity due to shorter distances could not
be demonstrated unequivocally.
Catfi shes are ideal candidates for studying the infl uence of swim bladder morphology, especially regarding organ size on hearing, because their bladders are
always connected to the inner ear. The interfamilial study by Lechner and Ladich
( 2008 ) showed that swim bladder size and distance affect hearing in catfi shes. A
larger swim bladder increases sensitivity from 1 to 6 kHz, but a shorter distance
between the bladder and the inner ear (based on a shorter ossicular chain) decreases
sensitivity. This is in contrast to our expectations that shorter distances improve
hearing but agrees with the observation in all other vertebrate classes that a higher
number of ossicles improves high-frequency hearing. Mammals possess three auditory ossicles and are on average able to detect much higher frequencies than anurans,
reptiles, or birds, which have only one middle ear ossicle (Ladich 2010 ). The intrafamilial study in thorny catfi shes by Zebedin and Ladich ( 2013 ) showed that the
infl uence of bladder size on hearing cannot be generalized. The hearing abilities
cannot be predicted when differences in swim bladder size are rather small.
Cichlids, in contrast, are the ideal fi sh family for studying both the effects of size
and distance because members of this family have large or vestigial swim bladders
and some species have connections between the swim bladder and inner ears.
Schulz-Mirbach et al. ( 2013 ) demonstrated that size and the presence of connections affect hearing in cichlids, but in different ways. Size affects the detectable
frequency range and a direct connection improves hearing sensitivity.
Finally, it needs to be mentioned that differences in auditory sensitivity between
closely related species may also refl ect factors other than peripheral hearing structures. Results from different studies need to be compared with caution due to potential differences in techniques applied in measuring hearing. Moreover, studies show
that the inner ear structure may be linked to peripheral hearing structures and that
differences in otolith size, size and form of sensory fi elds (maculae), as well as orientation patterns of sensory hair cells may affect hearing in parallel to peripheral
hearing structures (Ramcharitar et al. 2006 ; Popper and Schilt 2008 ; SchulzMirbach et al. 2014 ). An interesting task for future studies will be to show if and to
what degree particular inner ear structures help improve hearing in fi shes.
Acknowledgements This review is dedicated to Arthur N. Popper and Richard R. Fay to celebrate more than 45 years of work in fi sh bioacoustics. I am grateful to have the opportunity to work
and publish with both of them. Art invited me to his lab in 1998 and 1999 and introduced me to the
fi eld of inner ear structure in fi shes, which resulted in a common paper on labyrinth fi sh ears in
2001. Subsequently we wrote a review on the parallel evolution of fi sh hearing organs. This cooperation with Art on ears resulted years later in several studies of mine with colleagues in Germany.
Dick invited me to Fallmouth and Woods Hole in 1999. He impressed me by his knowledge in
vertebrate hearing (see his 1988 book) and his interests in all fi elds and techniques including the
auditory evoked potential (AEP) technique (which he never used). Our common “AEP” interest
resulted in 2013 in a review on the auditory evoked potential audiometry in fi shes in which we
compared behavioral to AEP data and summarized all studies published within the last 15 years.
Peripheral Hearing Structures in Fishes: Diversity and Sensitivity…