Inshore Fisheries Research Section

Using Otoliths to Age Fish

Otoliths are calcified structures that fish use for balance and orientation, much like the tubes of our inner ear. As the fish grows, so does the otolith.

Like a tree, fish lay down a new ring on their otoliths every day. The rings are proportional to the growth of the fish. When the fish grows quickly in the spring and summer months, these rings are wider than in winter when fish grow more slowly. Because these rings are laid down so close together during the slow growth of winter, a visible ring forms.

When we prepare otoliths for examination, we make a pencil mark through the core, or center, of the otolith. We then cut a cross section around the core using two blades. This thin wafer is then glued to a slide to be examined under a microscope.

As you can see below, this otolith has two distinct "rings", meaning this fish is two years old.