[2] Endolymphatic infillings such as otoliths are structures in the saccule and utricle of the inner ear, specifically in the vestibular labyrinth of all vertebrates (fish, amphibians, reptiles, mammals and birds).

Because of their orientation in the head, the utricle is sensitive to a change in horizontal movement, and the saccule gives information about vertical acceleration (such as when in an elevator).

Similar balance receptors called statocysts can be found in many invertebrate groups but are not contained in the structure of an inner ear.

The size of material that enters is limited to sand-sized particles and in the case of sharks is bound together with an endogenous organic matrix that the animal secretes.

In mammals, otoliths are small particles, consisting of a combination of a gelatinous matrix and calcium carbonate in the viscous fluid of the saccule and utricle.

[4] In humans vestibular evoked myogenic potentials occur in response to loud, low-frequency acoustic stimulation in patients with the sensorineural hearing loss.

[3] Vestibular sensitivity to ultrasonic sounds has also been hypothesized to be involved in the perception of speech presented at artificially high frequencies, above the range of the human cochlea (~18 kHz).

Fossil otoliths are rarely found in situ (on the remains of the animal), likely because they are not recognized separately from the surrounding rock matrix.

These rare cases are of special significance, since the presence, composition, and morphology of the material can clarify the relationship of species and groups.

[1] An unclassified fossil named Gluteus minimus has been thought to be possible otoliths, but it is hitherto unknown to which animal they could belong to.

A common tool used to measure trace elements in an otolith is a laser ablation inductively coupled plasma mass spectrometer.

In general, fish from highly structured habitats such as reefs or rocky bottoms (e.g. snappers, groupers, many drums and croakers) will have larger otoliths than fish that spend most of their time swimming at high speed in straight lines in the open ocean (e.g. tuna, mackerel, dolphinfish).

Otoliths, unlike scales, do not reabsorb during times of decreased energy making it even more useful tool to age a fish.

Due to the amount of required human labour in otolith age reading, there is active research in automating that process.

Separating recovered otoliths into right and left, therefore, allows one to infer a minimum number of prey individuals ingested for a given fish species.

They may suffer partial or complete erosion in the digestive tract, skewing measurements of prey number and biomass.

[23] The inclusion of fish vertebrae, jaw bones, teeth, and other informative skeletal elements improves prey identification and quantification over otolith analysis alone.

[25] 'Sea gems' ornaments from fish otoliths have been introduced in the market in India recently, with the efforts of a group of enthusiastic fisher women in Vizhinjam.

Ornaments from fish otoliths, known to the Romans and Egyptians as lucky stones, are continued to be used in countries like Brazil and the Faeröer, and are being collected and sold in an organized and sustainable manner in India.