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. Examination of the otoliths of orange roughy have revealed that they can grow to be over 100 years old.