Otolith

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Otolith
Otolith organs showing detail of utricle, otoconia, endolymph, cupula, macula, hair cell filaments, and saccular nerve
Juvenile herring. Length 30 mm; 3 months old; still transparent; the otoliths are visible left of the eye.
Details
Identifiers
Latinstatoconium
TA98A15.3.03.086
FMA77826
Anatomical terminology

An otolith (Greek: ὠτο-, ōto- ear + λῐ́θος, líthos, a stone), also called statoconium or otoconium or statolith, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule and utricle, in turn, together make the otolith organs. These organs are what allows an organism, including humans, to perceive linear acceleration, both horizontally and vertically (gravity). They have been identified in both extinct and extant vertebrates.[1]

Counting the annual growth rings on the otoliths is a common technique in

estimating the age of fish.[2]

Description

Endolymphatic infillings such as otoliths are structures in the

vestibular labyrinth of all vertebrates (fish, amphibians, reptiles, mammals and birds). In vertebrates, the saccule and utricle together make the otolith organs. Both statoconia and otoliths are used as gravity, balance, movement, and directional indicators in all vertebrates and have a secondary function in sound detection in higher aquatic and terrestrial vertebrates.[3][4] They are sensitive to gravity and linear acceleration. 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

Mollusk statocysts are of a similar morphology to the displacement-sensitive organs of vertebrates;[5] however, the function of the mollusk statocyst is restricted to gravity detection and possibly some detection of angular momentum.[6] These are analogous structures, with similar form and function but not descended from a common structure
.

Statoconia (also called otoconia) are numerous grains, often

µm; collectively.[citation needed] Statoconia are also sometimes termed a statocyst. Otoliths (also called statoliths) are agglutinated crystals or crystals precipitated around a nucleus, with well defined morphology and together all may be termed endolymphatic infillings.[1][7][8]

neoscopelid otoliths (Neoscopelus, right side) [9]

Mechanism

The

sharks) end in small openings, called endolymphatic pores, on the dorsal surface of the head.[1]
Extrinsic grains may enter through these openings, typically less than a millimeter in diameter. 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. The weight and inertia of these small particles causes them to stimulate hair cells when the head moves. The hair cells are made up of 40 to 70 stereocilia and one kinocilium, which is connected to an afferent nerve. Hair cells send signals down sensory nerve fibers which are interpreted by the brain as motion. In addition to sensing acceleration of the head, the otoliths can help to sense the orientation via gravity's effect on them. When the head is in a normal upright position, the otolith presses on the sensory hair cell receptors. This pushes the hair cell processes down and prevents them from moving side to side. However, when the head is tilted, the pull of gravity on otoliths shifts the hair cell processes to the side, distorting them and sending a message to the central nervous system that the head is tilted.

There is evidence that the vestibular system of mammals has retained some of its ancestral acoustic sensitivity and that this sensitivity is mediated by the otolithic organs (most likely the sacculus, due to its anatomical location). In mice lacking the otoconia of the utricle and saccule, this retained acoustic sensitivity is lost.[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).[10] In mice, sensation of acoustic information via the vestibular system has been demonstrated to have a behaviourally relevant effect; response to an elicited acoustic startle reflex is larger in the presence of loud, low frequency sounds that are below the threshold for the mouse cochlea (~4 Hz), raising the possibility that the acoustic sensitivity of the vestibular system may extend the hearing range of small mammals.[4]

Paleontology

After the death and decomposition of a fish, otoliths may be preserved within the body of an organism or be dispersed before burial and

endolymphatic infillings were similar in elemental composition to the rock matrix but were restricted to coarse grained material, which presumably is better for the detection of gravity, displacement, and sound. The presence of these extrinsic grains in osteostracans, chondrichthyans, and acanthodians indicates a common inner ear physiology and presence of open endolymphatic ducts.[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.

Ecology

Composition

Animation of the biomineralization of cod otoliths

The composition of fish otoliths is also proving useful to fisheries scientists. The calcium carbonate that the otolith is composed of is primarily derived from the water. As the otolith grows, new calcium carbonate crystals form. As with any crystal structure, lattice vacancies will exist during crystal formation allowing trace elements from the water to bind with the otolith. Studying the trace elemental composition or

isotopic signatures of trace elements within a fish otolith gives insight to the water bodies fish have previously occupied.[11] Fish otoliths as old as 172 million years have been used to study the environment in which the fish lived.[12] Robotic micromilling devices have also been used to recover very high resolution records of life history, including diet and temperatures throughout the life of the fish, as well as their natal origin.[13]

The most studied trace and isotopic signatures are strontium due to the same charge and similar ionic radius to calcium; however, scientists can study multiple trace elements within an otolith to discriminate more specific signatures. A common tool used to measure trace elements in an otolith is a laser ablation inductively coupled plasma mass spectrometer. This tool can measure a variety of trace elements simultaneously. A secondary ion mass spectrometer can also be used. This instrument can allow for greater chemical resolution but can only measure one trace element at a time. The hope of this research is to provide scientists with valuable information on where fish have frequented. Combined with otolith annuli, scientists can add how old fish were when they traveled through different bodies of water. This information can be used to determine fish life cycles so that fisheries scientists can make better informed decisions about fish stocks.

Growth rate and age

Pacific Cod
(Gadus macrocephalus)
red snapper
to determine its age
See also:
Estimating the age of fish

Finfish (class Osteichthyes) have three pairs of otoliths – the sagittae (singular sagitta), lapilli (singular lapillus), and asterisci (singular asteriscus). The sagittae are largest, found just behind the eyes and approximately level with them vertically. The lapilli and asterisci (smallest of the three) are located within the semicircular canals. The sagittae are normally composed of aragonite (although vaterite abnormalities can occur[14]
), as are the lapilli, while the asterisci are normally composed of vaterite.

The shapes and proportional sizes of the otoliths vary with fish species. In general, fish from highly structured habitats such as reefs or rocky bottoms (e.g.

dolphinfish). Flying fish
have unusually large otoliths, possibly due to their need for balance when launching themselves out of the water to "fly" in the air. Often, the fish species can be identified from distinct morphological characteristics of an isolated otolith.

Fish otoliths accrete layers of

tree rings. By counting the rings, it is possible to determine the age of the fish in years.[15] Typically the sagitta is used, as it is largest,[16]
but sometimes lapilli are used if they have a more convenient shape. The asteriscus, which is smallest of the three, is rarely used in age and growth studies.

In addition, in most species the accretion of calcium carbonate and gelatinous matrix alternates on a daily cycle. It is therefore also possible to determine fish age in days.[17] This latter information is often obtained under a microscope, and provides significant data to early life history studies.

By measuring the thickness of individual rings, it has been assumed (at least in some species) to estimate fish growth because fish growth is directly proportional to otolith growth.[18] However, some studies disprove a direct link between body growth and otolith growth. At times of lower or zero body growth the otolith continues to accrete leading some researchers to believe the direct link is to metabolism, not growth per se. Otoliths, unlike scales, do not reabsorb during times of decreased energy making it even more useful tool to age a fish. Fish never stop growing entirely, though growth rate in mature fish is reduced. Rings corresponding to later parts of the life cycle tend to be closer together as a result. Furthermore, a small percentage of otoliths in some species bear deformities over time.[19]

Age and growth studies of fish are important for understanding such things as timing and magnitude of spawning, recruitment and habitat use, larval and juvenile duration, and population age structure. Such knowledge is in turn important for designing appropriate fisheries management policies. Due to the amount of required human labour in otolith age reading, there is active research in automating that process.[20]

Diet research

Since the compounds in fish otoliths are resistant to

walruses. Many fish can be identified to genus and species
by their otoliths. Otoliths can therefore, to some extent, be used to deduce and reconstruct the prey composition of marine mammal and seabird diets.

Otoliths (sagittae) are

bilaterally symmetrical, with each fish having one right and one left. Separating recovered otoliths into right and left, therefore, allows one to infer a minimum number of prey individuals ingested for a given fish species. Otolith size is also proportional to the length and weight of a fish. They can therefore be used to back-calculate prey size and biomass, useful when trying to estimate marine mammal prey consumption, and potential impacts on fish stocks.[21]

Otoliths cannot be used alone to reliably estimate

taxa.[23]

The inclusion of fish

vertebrae, jaw bones, teeth, and other informative skeletal elements improves prey identification and quantification over otolith analysis alone.[24] This is especially true for fish species with fragile otoliths, but other distinctive bones, such as Atlantic mackerel (Scomber scombrus), and Atlantic herring (Clupea harengus).[25]

Otolith ornaments

'Sea gems'ornaments from fish otoliths have been introduced in the market for the first time, with the efforts of a group of enthusiastic fisher women in Vizhinjam. Scientists from Central Marine Fisheries Research Institute (CMFRI) have trained these fisher-women. Otoliths are important in fish studies ,as they have species -specific shapes and grow throughout their life. Fish Otoliths which are biomineralised ear stones provide sense of balance and help fish hear. Ornaments from fish otoliths, known to the Romans and Egyptians as lucky stones and are continued to be used in countries like Brazil, are being produced and sold in an organized and sustainable manner in India. [26]

See also

References

Wikimedia Commons has media related to Otoliths.
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  7. ^ Nolf, D. 1985. Otolithi Piscium; in H.-P. Schultze (ed.), Handbook of Paleoichthyology, Vol. 10. Gustav Fischer Verlag, Stuttgart, 145pp.
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  11. ISBN 9781118664025. {{cite book}}: |journal= ignored (help
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  16. ^ Fish Age and Growth with Otoliths Tennessee Wildlife Resources Agency. Retrieved 2007-04-07.
  17. ^ Bos, A.R. (1999). "Tidal transport of flounder larvae (Pleuronectes flesus) in the River Elbe, Germany". Archive of Fishery and Marine Research. 47 (1): 47–60.
  18. ^ Jones, Cynthia M. (1992). "Development and application of the otolith increment technique". In D. K. Stevenson; S.E. Campana (eds.). Otolith microstructure examination and analysis. Vol. 117. pp. 1–11. {{cite book}}: |work= ignored (help)
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  24. ^ Browne, Patience; Laake, Jeffrey L.; DeLong, Robert L. (2002). "Improving pinniped diet analyses through identification of multiple skeletal structures in fecal samples" (PDF). Fishery Bulletin. 100 (3): 423–433.
  25. ^ Ouwehand, J.; Leopold, M. F.; Camphuysen, C. J. (2004). "A comparative study of the diet of Guillemots Uria aalge and Razorbills Alca torda killed during the Tricolor oil incident in the south-eastern North Sea in January 2003" (PDF). Atlantic Seabirds. 6 (3): 147–163. Archived from the original (PDF) on August 6, 2020.
  26. ^ "FISH OTOLITH ORNAMENTS MAKE MARKET DEBUT". Universal Group Of Institutions. 31 March 2024. Retrieved 31 March 2024.

External links

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