407
discrimination between conspecifi c or heterospecifi c sounds that might differ subtly
in terms of temporal patterning or frequency.
Some fi sh species are not known to produce sound. It has been hypothesized that
the evolution of hearing in fi sh may not have been for communication per se, but
rather to gain acoustical information from the surrounding environment, i.e., the
auditory scene (Fay and Popper 1999 ). These sounds could have a physical source,
such as wave and tidal action, or be biological, such as the sounds produced by
predators or prey. Although data is still very limited, it is possible that hearing loss
could have negative consequences on a fi sh’s ability to forage, reproduce, avoid
predators, and orient in their environment, thus affecting their fi tness.
7 Regeneration of Sensory Hair Cells and Recovery
from Auditory Defi cits
In the 1980s it was discovered that the number of inner ear hair cells of elasmobranch and teleost fi shes increased for several years into adulthood (Corwin 1981 ,
1983 ; Popper and Hoxter 1984 ). This also suggested that fi sh may have the ability
to regenerate sensory hair cells. Lombarte et al. ( 1993 ) were the fi rst to document
hair cell regeneration in a fi sh. They showed that treatment with gentamicin sulfate
caused hair cell loss in the striolar regions of the utricle and lagena of the oscar.
However hair cell ciliary bundles recovered to control level densities within approximately 10 days following maximal hair cell loss.
Similarly, after 21 days of exposure to 160–170 dB re 1 μPa white noise, goldfi sh
which initially exhibited an average TTS of 18 dB recovered to control levels within
14 days (Smith et al. 2004a ). Much of this recovery occurred within the fi rst 7 days,
as in goldfi sh exposed to the same stimulus for only 2 days (Smith et al. 2006 ).
Although recovery of hearing was within 4 dB of control levels 7 days postexposure, caudal saccular hair cell densities had still not returned to normal after 8
days, suggesting that a full set of hair cells are not necessary for normal auditory
responses, at least in terms of AEPs (Fig. 7 ; Smith et al. 2006 ). Fathead minnows
( Pimephales promelas ) exposed to 142 dB re 1 μPa white noise for 2 h had thresholds that returned to control levels within 6 days following sound exposure while
those exposed for 24 h did not completely recover after 14 days (Scholik and Yan
2001 ). In another goldfi sh study, fi sh exposed for 12–24 h returned to control levels
within 3 days (Amoser and Ladich 2003 ). Obviously, the time course for recovery
from hearing loss will likely depend upon the species being examined and its normal hearing sensitivity, the sound exposure intensity and duration, and the amount
of sensory epithelial damage and hearing loss that is induced by the acoustic trauma.
No permanent hearing loss has been reported for fi shes as long-term acoustic
studies are typically not performed and fi sh inner ear hair cells have the ability to
regenerate (Smith et al. 2006 ; Schuck and Smith 2009 ; Schuck et al. 2011 ). The
longest time following a noise exposure in which the inner ear sensory cells of a fi sh
have been examined is 58 days. McCauley et al. ( 2003 ) exposed pink snapper
Causes and Consequences of Sensory Hair Cell Damage and Recovery in Fishes
discrimination between conspecifi c or heterospecifi c sounds that might differ subtly
in terms of temporal patterning or frequency.
Some fi sh species are not known to produce sound. It has been hypothesized that
the evolution of hearing in fi sh may not have been for communication per se, but
rather to gain acoustical information from the surrounding environment, i.e., the
auditory scene (Fay and Popper 1999 ). These sounds could have a physical source,
such as wave and tidal action, or be biological, such as the sounds produced by
predators or prey. Although data is still very limited, it is possible that hearing loss
could have negative consequences on a fi sh’s ability to forage, reproduce, avoid
predators, and orient in their environment, thus affecting their fi tness.
7 Regeneration of Sensory Hair Cells and Recovery
from Auditory Defi cits
In the 1980s it was discovered that the number of inner ear hair cells of elasmobranch and teleost fi shes increased for several years into adulthood (Corwin 1981 ,
1983 ; Popper and Hoxter 1984 ). This also suggested that fi sh may have the ability
to regenerate sensory hair cells. Lombarte et al. ( 1993 ) were the fi rst to document
hair cell regeneration in a fi sh. They showed that treatment with gentamicin sulfate
caused hair cell loss in the striolar regions of the utricle and lagena of the oscar.
However hair cell ciliary bundles recovered to control level densities within approximately 10 days following maximal hair cell loss.
Similarly, after 21 days of exposure to 160–170 dB re 1 μPa white noise, goldfi sh
which initially exhibited an average TTS of 18 dB recovered to control levels within
14 days (Smith et al. 2004a ). Much of this recovery occurred within the fi rst 7 days,
as in goldfi sh exposed to the same stimulus for only 2 days (Smith et al. 2006 ).
Although recovery of hearing was within 4 dB of control levels 7 days postexposure, caudal saccular hair cell densities had still not returned to normal after 8
days, suggesting that a full set of hair cells are not necessary for normal auditory
responses, at least in terms of AEPs (Fig. 7 ; Smith et al. 2006 ). Fathead minnows
( Pimephales promelas ) exposed to 142 dB re 1 μPa white noise for 2 h had thresholds that returned to control levels within 6 days following sound exposure while
those exposed for 24 h did not completely recover after 14 days (Scholik and Yan
2001 ). In another goldfi sh study, fi sh exposed for 12–24 h returned to control levels
within 3 days (Amoser and Ladich 2003 ). Obviously, the time course for recovery
from hearing loss will likely depend upon the species being examined and its normal hearing sensitivity, the sound exposure intensity and duration, and the amount
of sensory epithelial damage and hearing loss that is induced by the acoustic trauma.
No permanent hearing loss has been reported for fi shes as long-term acoustic
studies are typically not performed and fi sh inner ear hair cells have the ability to
regenerate (Smith et al. 2006 ; Schuck and Smith 2009 ; Schuck et al. 2011 ). The
longest time following a noise exposure in which the inner ear sensory cells of a fi sh
have been examined is 58 days. McCauley et al. ( 2003 ) exposed pink snapper
Causes and Consequences of Sensory Hair Cell Damage and Recovery in Fishes