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1 Introduction
All fi shes (except lampreys and hagfi shes) possess inner ears consisting of three
semicircular canals and three otolithic endorgans (utricle, saccule, lagena) (Retzius
1881 ; Platt and Popper 1981 ; Popper 2011 ). These otolithic endorgans enable fi sh
to detect particle motion in a sound fi eld at low frequencies (up to a few hundred
hertz) (Hawkins 1986 ; Ladich and Popper 2004 ). Interestingly, ray-fi nned bony
fi shes (class Actinopterygii) evolved numerous ways to connect the inner ears with
air-fi lled cavities within the body which are primarily used for other purposes such
as buoyancy and air-breathing (Braun and Grande 2008 ). The general notion is that
these connections improve hearing due to the ability of fi sh to detect pressure fl uctuations in a sound fi eld by transmitting volume changes in their gas-fi lled cavities
in various ways to the inner ears (Hawkins 1986 ). The ability to detect sound pressure changes in the far fi eld, besides particle motion detection in the near fi eld,
enables numerous taxa to extend their hearing range up to several kilohertz and their
hearing sensitivities down to low sound levels. In numerous species where such
connections have been described, the auditory function of these structures has not
been determined (Braun and Grande 2008 ; Ladich 2014 ).
Evidence for the notion that a particular peripheral (accessory or ancillary) structure
improves hearing came from numerous elimination experiments starting in the early
twentieth century by Karl von Frisch and his collaborators (von Frisch and Stetter
1932 ; von Frisch 1936 , 1938 ; Schneider 1941 ). In most cases peripheral structures
for hearing were eliminated either completely or by removing air from the bladder
and/or by fi lling the bladder with fl uids (Kleerekoper and Roggenkamp 1959 ; Fay
and Popper 1974 , 1975 ; Yan and Curtsinger 2000 ; Yan et al. 2000 ). In two investigations,
only the connections to the inner ear were interrupted and the swim bladders were
left intact. Poggendorf ( 1952 ) and Ladich and Wysocki ( 2003 ) extirpated the tripus,
the largest auditory ossicles in otophysines. Results from elimination experiments
typically showed a decrease in auditory sensitivities but were very contradictory
with regard to the amount of the decline in sensitivity at different frequencies.
Poggendorf ( 1952 ) observed a rather similar decrease in hearing of about 30 and 40
dB between 60 Hz and 6 kHz in the brown bullhead Ictalurus nebulosus , whereas
Ladich and Wysocki ( 2003 ) found a frequency-dependent hearing loss in the goldfi sh
ranging from 7 dB at 100 Hz to 33 dB at 2 kHz.
Three major types (each with numerous subtypes) of peripheral structures for
improved hearing can be distinguished in bony fi shes (Fig. 1 ). Numerous groups
such as sciaenids or holocentrids possess swim bladder extensions that protrude anteriorly to contact the occipital bones or even the inner ears in different ways (Coombs
and Popper 1979 , 1982 ; Ramcharitar et al. 2004 , 2006 ; Schulz-Mirbach et al. 2013 )
(Fig. 1a ). In holocentrids in general there is no relationship between the swim bladder and the auditory bullae, an enlarge portion of the otic region of the skull. Some
representatives, however, possess a direct relationship between anterior end of the
bladder and the membranous areas of the auditory bullae. Finally, in the subfamily
Myripristinae there exists an intimate contact between the anterior extensions of the
bladder and the membranous areas of the enlarged auditory bullae (Nelson 1955 ).
F. Ladich
1 Introduction
All fi shes (except lampreys and hagfi shes) possess inner ears consisting of three
semicircular canals and three otolithic endorgans (utricle, saccule, lagena) (Retzius
1881 ; Platt and Popper 1981 ; Popper 2011 ). These otolithic endorgans enable fi sh
to detect particle motion in a sound fi eld at low frequencies (up to a few hundred
hertz) (Hawkins 1986 ; Ladich and Popper 2004 ). Interestingly, ray-fi nned bony
fi shes (class Actinopterygii) evolved numerous ways to connect the inner ears with
air-fi lled cavities within the body which are primarily used for other purposes such
as buoyancy and air-breathing (Braun and Grande 2008 ). The general notion is that
these connections improve hearing due to the ability of fi sh to detect pressure fl uctuations in a sound fi eld by transmitting volume changes in their gas-fi lled cavities
in various ways to the inner ears (Hawkins 1986 ). The ability to detect sound pressure changes in the far fi eld, besides particle motion detection in the near fi eld,
enables numerous taxa to extend their hearing range up to several kilohertz and their
hearing sensitivities down to low sound levels. In numerous species where such
connections have been described, the auditory function of these structures has not
been determined (Braun and Grande 2008 ; Ladich 2014 ).
Evidence for the notion that a particular peripheral (accessory or ancillary) structure
improves hearing came from numerous elimination experiments starting in the early
twentieth century by Karl von Frisch and his collaborators (von Frisch and Stetter
1932 ; von Frisch 1936 , 1938 ; Schneider 1941 ). In most cases peripheral structures
for hearing were eliminated either completely or by removing air from the bladder
and/or by fi lling the bladder with fl uids (Kleerekoper and Roggenkamp 1959 ; Fay
and Popper 1974 , 1975 ; Yan and Curtsinger 2000 ; Yan et al. 2000 ). In two investigations,
only the connections to the inner ear were interrupted and the swim bladders were
left intact. Poggendorf ( 1952 ) and Ladich and Wysocki ( 2003 ) extirpated the tripus,
the largest auditory ossicles in otophysines. Results from elimination experiments
typically showed a decrease in auditory sensitivities but were very contradictory
with regard to the amount of the decline in sensitivity at different frequencies.
Poggendorf ( 1952 ) observed a rather similar decrease in hearing of about 30 and 40
dB between 60 Hz and 6 kHz in the brown bullhead Ictalurus nebulosus , whereas
Ladich and Wysocki ( 2003 ) found a frequency-dependent hearing loss in the goldfi sh
ranging from 7 dB at 100 Hz to 33 dB at 2 kHz.
Three major types (each with numerous subtypes) of peripheral structures for
improved hearing can be distinguished in bony fi shes (Fig. 1 ). Numerous groups
such as sciaenids or holocentrids possess swim bladder extensions that protrude anteriorly to contact the occipital bones or even the inner ears in different ways (Coombs
and Popper 1979 , 1982 ; Ramcharitar et al. 2004 , 2006 ; Schulz-Mirbach et al. 2013 )
(Fig. 1a ). In holocentrids in general there is no relationship between the swim bladder and the auditory bullae, an enlarge portion of the otic region of the skull. Some
representatives, however, possess a direct relationship between anterior end of the
bladder and the membranous areas of the auditory bullae. Finally, in the subfamily
Myripristinae there exists an intimate contact between the anterior extensions of the
bladder and the membranous areas of the enlarged auditory bullae (Nelson 1955 ).
F. Ladich