Age-Related Changes in Zebrafish Hearing
Zebrafish have become
an extremely important vertebrate genetic model system. In studies
of zebrafish, a significant number of genes have been identified
which impact the development of the ear in various ways. Presumably,
the ultimate impact of these genes could be on the auditory or vestibular
In order to assess how
genes impact the function of the ear it is necessary to have basic
information on normal ear function in young and adult animals. Over
the past several years, our lab has been studying hearing in zebrafish,
with the goal of defining normal hearing capabilities in adult animals,
and during development.
one investigation (see figure to the left) we explored the number
of sensory hair cells in the ear of fishes of different ages (Higgs
et al., 2001).
We found that zebrafish, as other fishes, continues to add sensory
hair cells for a long time after hatching. However, unlike a number
of other species we have studied, including the oscar and hake,
there is a point where there is no longer an increase in the number
of hair cells. At the same time, we did find, using BrdU and TUNEL
studies, that hair cell death and proliferation continues past the
age at which there is no longer hair cell addition, suggesting a
turn-over in hair cells in the zebrafish saccule.
An important discovery
was that fish kept in crowded conditions had far fewer sensory cells
in the saccule than fishes kept in uncrowded conditions. These results
suggest that fish kept in crowded conditions do not develop normally.
the ABR method, the same study measured hearing capabilities in
fishes of different sizes. As shown in the hearing study shown at
the left, there was a significant increase in bandwidth of hearing
in as they get larger, at least starting after 20 mm in total length.
Hearing in adult zebrafish is from below 100 Hz (the lower limits
of our setup) to about 4,000 Hz. This is a frequency range typical
of other members of the Otophysans, the group of hearing specialists
which includes zebrafish, goldfish, and catfish.