or "earstones" are stones that grow just behind the brain of many fishes, excluding sharks, rays and skates. There are three pairs of otoliths and they are used in the fish's hearing. The largest of the otolith pairs are called sagittae and these are what most people refer to as otoliths.
Otoliths are made of calcium carbonate in the mineral form aragonite. Otoliths grow as concentric layers of calcium carbonate are deposited over time. Where the growth rate of rings is known, the number of rings can be used to determine a fish's age. To see the rings, the otoliths are carefully cut open and thinly sliced to reveal the inner rings.
Because the otoliths are more durable than the soft flesh of the fish, otoliths are commonly found in recent sediments and as fossils in sedimentary strata. Otoliths found in sediment and rock offer clues to the changes in the population of fishes and environmental conditions in the past.
Location of otoliths.
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