Hair Cell Orientation Patterns in Fish Saccules

These figures demonstrate hair cell orientation patterns that are found in the ear of fishes. The top figure shows the ciliary bundles on the saccule of a lizard fish. Each ciliary bundle contains a single kinocilium at one end of the bundle and a larger number of stereocilia. The dashed line in this scanning electron micrograph separates ciliary bundles that are oriented with the kinocilium to the top (left) with those oriented towards the bottom (right). The bottom figure illustrates a variety of different saccular hair cell orientation patterns from different species.

The drawing on the right shows the saccular hair cell orientation patterns that we have identified in different fishes. The dashed lines show the dividing lines between orientation groups while the arrows indicate the location of the kinocilum (and thus the orientation) of most of the hair cells in each region of the epithelium (or macula). The 'standard' pattern is found in most species that are hearing 'generalists', or species that don't have any specilaizations for hearing. The other patterns are found in a variety of fish species that have specializations to enhance hearing capabilities. The patterns are not necessarily taxonomically related, and the same pattern may be found in taxonomically diverse species. For example, the 'vertical' pattern is found in all otophysan fishes (goldfish and relatives) and also in the unrelated mormyrids.