Analysis: Whole Otolith Aging

In order to see the annuli clearly on a whole otolith, the sulcus must be facing down, and the otolith must be well hydrated. If not freshly removed, soak the otolith in water for a couple of hours. (If time allows, soak it overnight or for several days). While viewing under the microscope, keep the otolith in a drop of water.

The preferred lighting for this process in reflected. This will produce dark annuli and large white areas of growth. When using transmitted light (from below) it is harder to distinguish the annuli due to the thickness of the otolith; the light will not be able to sine through the otolith in most cases. When it does, you will see the annuli as light bands-just the opposite of the dark bands you see using reflected light. In some cases, you can view the annuli using horizontal lighting. There will be a raised edge at the formation of each annulus. However, in many cases the surface of the otolith is relatively smooth and will not show any relief.

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