The first step in preparing the otolith is breaking it as closely through the center as possible. I used my fingers to break them in half, but many people use forceps or a hard surface to crack them open. A good break will allow you to view each annulus (yearly growth ring). Next, and most importantly, is the burning procedure. Using lighters, we burned the otolith until we achieved a uniform dark brown. This turns the annuli dark brown and keeps the remainder of the otolith light, giving you distinction between years. Then we added a dab of mineral oil for clarity and had a perfectly prepared otolith to read.
In the photo above, you can see the distinction between the dark brown annuli and the light summer growth. This otolith is from a mature 13-year-old prickly sculpin. As fish mature, they experience a change in growth rate. You can see this by the small separation of annuli in this adult. In juvenile fish, the translucent growth zones are much larger than those later in life (see center of the image).
We have finished all the aging for this study and will now move on to analyzing our data with the environmental and biological information we collected about the fish and their habitats early this year.
--Timothy Grun, Biological Science Technician