398
behavioral hearing thresholds at 500 and 800 Hz. This caused temporary threshold
shifts (TTS) that varied depending upon stimulation and test frequency, but hearing
thresholds returned to normal within a day. Sensory hair cell loss in a fi sh was fi rst
reported by Enger ( 1981 ), who exposed Atlantic cod ( Gadus morhua ) to tones
between 50 and 400 Hz that were 100–110 dB above the most sensitive hearing
threshold of cod. Immediately following a 1–5 h exposure, saccules were prepared
for scanning electron microscopy. Enger found that large patches of hair cells were
damaged, with a complete or almost complete lack of stereocilia, and that lower
frequency tones damaged the caudal portion of the saccule while higher frequencies
damaged the rostral saccule. More recent studies have generally focused on the
effects of anthropogenic sounds on fi shes, an interest which began in the early 1990s
when high intensity underwater sounds were fi rst projected across oceans to assess
global warming (Baggeroer and Munk 1992 ). Although initial concerns focused on
the potentially negative impacts of these sounds on marine mammals (Richardson
et al. 1995 ), this naturally led to studies on other aquatic organisms such as fi shes.
In 1996 , Hastings et al. exposed oscars ( Astronotus ocellatus ) to pure tones that
varied in frequency (60 or 300 Hz), duty cycle (20 % or continuous), and intensity
(100, 140, or 180 dB re 1 μPa) and examined the hair cells of the inner ear and lateral line. They found that fi sh exposed to a continuous 300 Hz tone exhibited limited damage in small regions of the utricle and lagena. The examination of hair cell
damage was later coupled with the recording of auditory evoked potentials (AEP) to
perform auditory testing on sound-exposed fi sh. This method allowed hearing tests
on fi shes to be performed relatively quickly and effi ciently compared to standard
behavioral methods (Corwin et al. 1982 ; Kenyon et al. 1998 ).
Sound-induced hearing loss has been reported in a number of fi sh species [e.g.,
goldfi sh, Carassius auratus (Amoser and Ladich 2003 ; Smith et al. 2004a , b ); fathead minnows, Pimephales promelas (Scholik and Yan 2001 , 2002a ); northern
pike, Esox Lucius ; lake chub, Couesius plumbeus (Popper et al. 2005 ); Pimelodus
pictus (Amoser and Ladich 2003 ); sailfi n molly, Poecilia latipinna , and koi,
Cyprinus carpio (Coffey 2014 )], while other species exhibited no or minimal hearing threshold shifts following intense sound exposure [bluegill sunfi sh, Lepomis
macrochirus (Scholik and Yan 2002b ); Oreochromis niloticus (Smith et al. 2004b );
rainbow trout, Oncorhynchus mykiss (Wysocki et al. 2007 )].
Using goldfi sh as an experimental model, general patterns for sound-induced
hearing loss have been found. First, hearing loss, as measured in decibels of TTS,
increases with duration of noise exposure and decreases, i.e., recovers, with time
post-exposure (Smith et al. 2004a , 2006 ; Popper et al. 2004 ). Second, TTS increases
linearly with sound pressure level (SPL) of the stimulus (Fig. 3 ; Smith et al. 2004b ).
Third, fi sh tend to exhibit the greatest hearing loss at frequencies where they are the
most sensitive such that the curve of TTS across frequency has a shape that is the
inverse of the control audiogram of the fi sh (Smith et al. 2004b , 2006 , 2011 ). As a
result, it has been suggested that researchers should use the SPL difference between
the intensity of sound stimuli and the baseline hearing threshold level as a means of
predicting threshold shifts instead of the actual SPL of the noise (Smith 2012 ).
Fourth, saccular hair cell loss is correlated with hearing loss, and hearing recovery
M.E. Smith and J.D. Monroe
behavioral hearing thresholds at 500 and 800 Hz. This caused temporary threshold
shifts (TTS) that varied depending upon stimulation and test frequency, but hearing
thresholds returned to normal within a day. Sensory hair cell loss in a fi sh was fi rst
reported by Enger ( 1981 ), who exposed Atlantic cod ( Gadus morhua ) to tones
between 50 and 400 Hz that were 100–110 dB above the most sensitive hearing
threshold of cod. Immediately following a 1–5 h exposure, saccules were prepared
for scanning electron microscopy. Enger found that large patches of hair cells were
damaged, with a complete or almost complete lack of stereocilia, and that lower
frequency tones damaged the caudal portion of the saccule while higher frequencies
damaged the rostral saccule. More recent studies have generally focused on the
effects of anthropogenic sounds on fi shes, an interest which began in the early 1990s
when high intensity underwater sounds were fi rst projected across oceans to assess
global warming (Baggeroer and Munk 1992 ). Although initial concerns focused on
the potentially negative impacts of these sounds on marine mammals (Richardson
et al. 1995 ), this naturally led to studies on other aquatic organisms such as fi shes.
In 1996 , Hastings et al. exposed oscars ( Astronotus ocellatus ) to pure tones that
varied in frequency (60 or 300 Hz), duty cycle (20 % or continuous), and intensity
(100, 140, or 180 dB re 1 μPa) and examined the hair cells of the inner ear and lateral line. They found that fi sh exposed to a continuous 300 Hz tone exhibited limited damage in small regions of the utricle and lagena. The examination of hair cell
damage was later coupled with the recording of auditory evoked potentials (AEP) to
perform auditory testing on sound-exposed fi sh. This method allowed hearing tests
on fi shes to be performed relatively quickly and effi ciently compared to standard
behavioral methods (Corwin et al. 1982 ; Kenyon et al. 1998 ).
Sound-induced hearing loss has been reported in a number of fi sh species [e.g.,
goldfi sh, Carassius auratus (Amoser and Ladich 2003 ; Smith et al. 2004a , b ); fathead minnows, Pimephales promelas (Scholik and Yan 2001 , 2002a ); northern
pike, Esox Lucius ; lake chub, Couesius plumbeus (Popper et al. 2005 ); Pimelodus
pictus (Amoser and Ladich 2003 ); sailfi n molly, Poecilia latipinna , and koi,
Cyprinus carpio (Coffey 2014 )], while other species exhibited no or minimal hearing threshold shifts following intense sound exposure [bluegill sunfi sh, Lepomis
macrochirus (Scholik and Yan 2002b ); Oreochromis niloticus (Smith et al. 2004b );
rainbow trout, Oncorhynchus mykiss (Wysocki et al. 2007 )].
Using goldfi sh as an experimental model, general patterns for sound-induced
hearing loss have been found. First, hearing loss, as measured in decibels of TTS,
increases with duration of noise exposure and decreases, i.e., recovers, with time
post-exposure (Smith et al. 2004a , 2006 ; Popper et al. 2004 ). Second, TTS increases
linearly with sound pressure level (SPL) of the stimulus (Fig. 3 ; Smith et al. 2004b ).
Third, fi sh tend to exhibit the greatest hearing loss at frequencies where they are the
most sensitive such that the curve of TTS across frequency has a shape that is the
inverse of the control audiogram of the fi sh (Smith et al. 2004b , 2006 , 2011 ). As a
result, it has been suggested that researchers should use the SPL difference between
the intensity of sound stimuli and the baseline hearing threshold level as a means of
predicting threshold shifts instead of the actual SPL of the noise (Smith 2012 ).
Fourth, saccular hair cell loss is correlated with hearing loss, and hearing recovery
M.E. Smith and J.D. Monroe