There are three ways of finding the age of a fish.
The easiest is by looking at its scales. Rings spreading out from the center of each scale show the periods of growth. The rings are farther apart in summer, when the fish grows faster, and closer in winter. A wide ring and a narrow ring equal one year in the fish's life. Age can also be found by looking at the operculum, or gill-covering, through a microscope. For each year of life the operculum will show one dark and one light band of shading.
Similar dark and light bands occur on the otoliths, the very small bones at the back of the fish's brain.