How do you age a fish? As it turns out, kind of like a tree... Otoliths (Greek for “ear-stone”) are calcium carbonate structures found beneath the brain of most fish that aid in balance and hearing. Otoliths continuously accrete calcium carbonate throughout the fish’s life, forming bands on the otolith -- much like rings of a tree. Scientists can use these bands to tell the age of a fish. Scott France, our science lead on our previous Voyage to the Ridge expedition, explains more in this video.