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been investigated regarding the development of auditory capabilities and sound
production in the context of acoustic communication, namely the croaking gourami
( T. vittata , Osphronemidae) (Wysocki and Ladich 2001 ), the Lusitanian toadfi sh
( Halobatrachus didactylus , Batrachoididae) (Vasconcelos and Ladich 2008 ), and
the squeaker catfi sh ( Synodontis schoutedeni , Mochokidae) (Lechner et al. 2010 ). In
each of these species, ontogenetic improvements in auditory sensitivity were coincident with changes in the spectral features of sound production, such as dominant
frequency and amplitude.
More specifi cally, as mentioned before, in the croaking gourami ( Trichopsis vittata ), auditory sensitivity increased up to 14 dB re 1 μPa between 0.8 and 3.0 kHz
and the most sensitive frequency within this range shifting from 2.5 to 1.5 kHz
(Wysocki and Ladich 2001 ). The authors of this study also reported that sound production in T. vittata began early in development (at 17.5 mm SL) and the dominant
frequency of vocalizations shifted from 3 to 1.5 kHz accompanied by an increase in
amplitude of 43 dB re 1 μPa. Such results suggested the onset of acoustic communication occurs only after improvements in both auditory sensitivity and vocal
amplitude around the same frequencies (circa 1.5 kHz).
In the Lusitanian toadfi sh ( H. didactylus ), the best hearing sensitivity was found
at 50 Hz for all sizes analyzed (from 3 to 32 cm SL) and auditory sensitivity
improved at 100 Hz, as well as, at higher frequencies such as 800 and 1000 Hz with
age/size (Vasconcelos and Ladich 2008 ). Comparing auditory thresholds with sound
spectra within each size group revealed that smaller juveniles were potentially
barely able to detect agonistic vocalizations of similar-sized fi sh, contrary to larger
fi sh. The authors suggested that the onset of acoustic communication occurs when
juveniles were able to generate grunts of higher sound amplitude and lower dominant frequency.
Finally, in the squeaker catfi sh ( S. schoutedeni ), auditory sensitivity increased at
higher frequencies during ontogeny, namely at 5 and 6 kHz, and comparisons
between audiograms and sound spectra revealed a match between that the most
sensitive hearing frequencies and the dominant frequencies of agonistic sounds for
all sizes analyzed (Lechner et al. 2010 ). This study showed that S. schoutedeni
could detect conspecifi c vocalizations at all developmental stages examined, most
likely due to the presence of the Weberian apparatus.
In these studies, all juvenile fi shes vocalized in agonistic context, showing
similar changes in sound features despite possessing different sound production
mechanisms. In all three studies the dominant frequency decreased with fi sh
development, whereas sound pressure levels and pulse periods increased throughout ontogeny. In both the croaking gourami and the squeaker catfi sh sound duration also increased throughout ontogeny. Future studies should analyze how the
vocal repertoire changes during development, especially in highly vocal species
such as the toadfi shes, and whether vocal differentiation parallels auditory
improvements.
R.O. Vasconcelos et al.
been investigated regarding the development of auditory capabilities and sound
production in the context of acoustic communication, namely the croaking gourami
( T. vittata , Osphronemidae) (Wysocki and Ladich 2001 ), the Lusitanian toadfi sh
( Halobatrachus didactylus , Batrachoididae) (Vasconcelos and Ladich 2008 ), and
the squeaker catfi sh ( Synodontis schoutedeni , Mochokidae) (Lechner et al. 2010 ). In
each of these species, ontogenetic improvements in auditory sensitivity were coincident with changes in the spectral features of sound production, such as dominant
frequency and amplitude.
More specifi cally, as mentioned before, in the croaking gourami ( Trichopsis vittata ), auditory sensitivity increased up to 14 dB re 1 μPa between 0.8 and 3.0 kHz
and the most sensitive frequency within this range shifting from 2.5 to 1.5 kHz
(Wysocki and Ladich 2001 ). The authors of this study also reported that sound production in T. vittata began early in development (at 17.5 mm SL) and the dominant
frequency of vocalizations shifted from 3 to 1.5 kHz accompanied by an increase in
amplitude of 43 dB re 1 μPa. Such results suggested the onset of acoustic communication occurs only after improvements in both auditory sensitivity and vocal
amplitude around the same frequencies (circa 1.5 kHz).
In the Lusitanian toadfi sh ( H. didactylus ), the best hearing sensitivity was found
at 50 Hz for all sizes analyzed (from 3 to 32 cm SL) and auditory sensitivity
improved at 100 Hz, as well as, at higher frequencies such as 800 and 1000 Hz with
age/size (Vasconcelos and Ladich 2008 ). Comparing auditory thresholds with sound
spectra within each size group revealed that smaller juveniles were potentially
barely able to detect agonistic vocalizations of similar-sized fi sh, contrary to larger
fi sh. The authors suggested that the onset of acoustic communication occurs when
juveniles were able to generate grunts of higher sound amplitude and lower dominant frequency.
Finally, in the squeaker catfi sh ( S. schoutedeni ), auditory sensitivity increased at
higher frequencies during ontogeny, namely at 5 and 6 kHz, and comparisons
between audiograms and sound spectra revealed a match between that the most
sensitive hearing frequencies and the dominant frequencies of agonistic sounds for
all sizes analyzed (Lechner et al. 2010 ). This study showed that S. schoutedeni
could detect conspecifi c vocalizations at all developmental stages examined, most
likely due to the presence of the Weberian apparatus.
In these studies, all juvenile fi shes vocalized in agonistic context, showing
similar changes in sound features despite possessing different sound production
mechanisms. In all three studies the dominant frequency decreased with fi sh
development, whereas sound pressure levels and pulse periods increased throughout ontogeny. In both the croaking gourami and the squeaker catfi sh sound duration also increased throughout ontogeny. Future studies should analyze how the
vocal repertoire changes during development, especially in highly vocal species
such as the toadfi shes, and whether vocal differentiation parallels auditory
improvements.
R.O. Vasconcelos et al.