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 senses.

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.

In 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.

Using 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.