How can growth rings help scientists estimate the age of fishes and clams?

In many species of fishes and certain types of clams, growth occurs in a seasonal manner. Because of this, these organisms produce annual zones of growth in their tissues that function similarly to growth rings found in trees.1

By observing these distinct annual layers, scientists can estimate the age of these animals. This method is particularly useful because, unlike domesticated species studied in controlled environments, it is often difficult to determine the natural life span of animals that move freely in the wild.1