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{{Infobox Anatomy |
Name = {{PAGENAME}} |
Latin = |
GraySubject = 232 |
GrayPage = 1054 |
Image = bigotolith.jpg |
Caption = illustration of otolith organs showing detail of utricle, ococonia, endolymph, cupula, macula, hair cell filaments, and saccular nerve |
Image2 = Herringjuvenilekils.jpg |
Caption2 = Juvenile [[Herring]]. Length ca 30 mm, ca. 3 months old - still transparent, visible are the otoliths left of the eyes. |
System = |
MeshName = Otolithic+Membrane |
MeshNumber = A09.246.631.909.625.125.680 |
An '''otolith''', (''oto-'', ear + ''lithos'', a stone), also called '''statoconium'''<ref>[ Dorland's Illustrated Medical Dictionary]</ref> or '''otoconium''' is a structure in the [[saccule]] or [[Utricle (ear)|utricle]] of the [[inner ear]], specifically in the [[Labyrinth (inner ear)|vestibular labyrinth]]. The saccule and utricle, in turn, together make the ''otolith organs''. They are sensitive to [[gravity]] and linear [[acceleration]]. Because of their orientation in the head, the [[Utricle (ear)|utricle]] is sensitive to a change in horizontal movement, and the [[saccule]] gives information about vertical acceleration (such as when in an [[elevator]]).
Otoliths are small particles, composed of a combination of a gelatinous matrix and [[calcium carbonate]] in the viscous fluid of the saccule and utricle. The [[inertia]] of these small particles causes them to stimulate hair cells when the head moves. The hair cells send signals down sensory nerve fibres, which are interpreted by the brain as motion.
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 statoconia shift the hair cell processes to the side, distorting them and sending a message to the [[central nervous system]] that the head is no longer level but now tilted.
In 1991, Martin Lenhardt of the [[University of Virginia]] discovered that people can hear [[ultrasonic]] speech, perhaps using the saccule as a hearing organ.<ref> {{cite journal|title=Human ultrasonic speech perception|journal=Science|date=1991-07-05|first=|last=Lenhardt|coauthors=|volume=253|issue=5015|pages=82-5|id= |url=|format=|accessdate=2007-02-02}}</ref>
==Significance in Ichthyology==
[[ray-finned 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 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. [[snapper | snappers]], [[grouper | groupers]], many [[Sciaenidae | 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]], [[Coryphaenidae | 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 [[calcium carbonate]] and gelatinous matrix throughout their lives. The accretion rate varies with growth of the fish - often less growth in winter and more in summer - which results in the appearance of rings that resemble [[tree rings]]. By counting the rings, it is possible to determine the age of the fish in years.<ref>[ Quality control of age data at the Alaska Fisheries Science Center (PDF)] Daniel K. Kimura, Delsa M. Anderl, Marine and Freshwater Research, 2005, 56, 783–789. Retrieved [[2007-04-07]].</ref> Typically the sagitta is used, as it is largest,<ref>[ Fish Age and Growth with Otoliths] Tennessee Wildlife Resources Agency. Retrieved [[2007-04-07]].</ref> 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.
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 [[age class structure | population age structure]]. Such knowledge is in turn important for designing appropriate [[fishery | fisheries]] management policies.
==See also==
<div class='references-small'>
{{Auditory and vestibular systems}}
[[Category:Auditory system]]
[[Category:Fish anatomy]]

Latest revision as of 12:34, October 9, 2013

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