135
was accompanied by a fundamental reorganization of otolithic membrane structure.
As reported by Lychakov and co-workers ( 2000 ):
“ the mass of the otolithic membrane and the length of the animal are power
related in elasmobranch fi shes. The otoconia of rays tend to be lemon shaped or
spherical, however, the dogfi sh has large, cuboidal (parallelepiped-shaped)
endogenous otoconia. The size of the endogenous otoconia does not depend on the
size of the animals. No specialized zones were found in rays either on the surface or
inside the otolithic membranes containing otoconia of one type or size. The data
indicate that the mass of the otolithic apparatus in rays increases on account of the
formation of new otoconia, ” (Lychakov et al. 2000 ).
On the cellular level, otoconia formation occurs outside the cells and therefore
depends on secretion of the required assembly components into the endolymphatic
spaces. The delicate balance between the organic and inorganic components of
otoconia, including their spatial and temporal distribution, determines the growth
rate, shape, and composition of the mineral (Dror et al. 2010 ). The organic fraction
of otoconia contains several matrix proteins (see below) that are critical for the
nucleation and mineralization of otoconia.
Thus, otoconia can exist as separate microparticles and in the form of otoconial mass. The otoconial mass observed in the endolymphatic sac of rays and
sharks represents some kind of loose aggregates. However, teleosts have the rigid
polycrystalline otolith. As suggested by Gauldie ( 1996 ), this transition from one
phase to another is probably occurred by “progressive fusion of otoconia from
a loose aggregate to a semi-rigid mass,” (Gauldie 1996 ). Electron microscopy
investigations of teleosts otoliths, show that sometimes examples of primitive
fused otoconia type of otolith still occur in the otherwise polycrystalline otoliths.
The morphological features of the fused otoconia are, probably, dependent of the
polymorphs of calcium carbonate which are involved, as well as the particular
crystal habit of these formations. It was suggested that “Ostwald ripening, KeithPadden spherulitic growth and carbonate cementation are signifi cant in the
chemistry of fusion of otoconia in the evolution of the aragonite teleost otolith, ”
(Gauldie 1996 ).
Both otoconia and otoliths can also occur simultaneously in fi sh organisms.
For example, both otoliths and otoconia consisting of crenelated spherules of
calcium carbonate have been identifi ed in four species of unrelated teleosts from
New Zealand waters: barracuda ( Thyristes atun ), leatherjacket (Parika scaber), the
tarakihi ( Cheilodactylus macropterus ), and red cod ( Pseudophycis bacchus )
(Gauldie et al. 1986 ). Note, that the “ critical function of otoconia and otoliths is to
impart inertial movements in response to gravity or linear acceleration, which
stimulates the underlying sensory hair cells by defl ecting their stereocilia bundles, ”
(Deans et al. 2010 ; see also Hudspeth 2008 ).
There are numerous publications on “earstones”, or otoliths which are defi ned
as “paired calcifi ed structures used for balance and/or hearing in all teleost fi shes,”
(Campana 1999 ; see also Campana 2004 ; Tuset et al. 2003 ). The “chemistry of
water” seems to be the crucial point for the basic pathway of the bulk of inorganic
elements into the crystalline structure like otolith. Gills or intestine are involved
3.3 Otoconia and Otoliths
was accompanied by a fundamental reorganization of otolithic membrane structure.
As reported by Lychakov and co-workers ( 2000 ):
“ the mass of the otolithic membrane and the length of the animal are power
related in elasmobranch fi shes. The otoconia of rays tend to be lemon shaped or
spherical, however, the dogfi sh has large, cuboidal (parallelepiped-shaped)
endogenous otoconia. The size of the endogenous otoconia does not depend on the
size of the animals. No specialized zones were found in rays either on the surface or
inside the otolithic membranes containing otoconia of one type or size. The data
indicate that the mass of the otolithic apparatus in rays increases on account of the
formation of new otoconia, ” (Lychakov et al. 2000 ).
On the cellular level, otoconia formation occurs outside the cells and therefore
depends on secretion of the required assembly components into the endolymphatic
spaces. The delicate balance between the organic and inorganic components of
otoconia, including their spatial and temporal distribution, determines the growth
rate, shape, and composition of the mineral (Dror et al. 2010 ). The organic fraction
of otoconia contains several matrix proteins (see below) that are critical for the
nucleation and mineralization of otoconia.
Thus, otoconia can exist as separate microparticles and in the form of otoconial mass. The otoconial mass observed in the endolymphatic sac of rays and
sharks represents some kind of loose aggregates. However, teleosts have the rigid
polycrystalline otolith. As suggested by Gauldie ( 1996 ), this transition from one
phase to another is probably occurred by “progressive fusion of otoconia from
a loose aggregate to a semi-rigid mass,” (Gauldie 1996 ). Electron microscopy
investigations of teleosts otoliths, show that sometimes examples of primitive
fused otoconia type of otolith still occur in the otherwise polycrystalline otoliths.
The morphological features of the fused otoconia are, probably, dependent of the
polymorphs of calcium carbonate which are involved, as well as the particular
crystal habit of these formations. It was suggested that “Ostwald ripening, KeithPadden spherulitic growth and carbonate cementation are signifi cant in the
chemistry of fusion of otoconia in the evolution of the aragonite teleost otolith, ”
(Gauldie 1996 ).
Both otoconia and otoliths can also occur simultaneously in fi sh organisms.
For example, both otoliths and otoconia consisting of crenelated spherules of
calcium carbonate have been identifi ed in four species of unrelated teleosts from
New Zealand waters: barracuda ( Thyristes atun ), leatherjacket (Parika scaber), the
tarakihi ( Cheilodactylus macropterus ), and red cod ( Pseudophycis bacchus )
(Gauldie et al. 1986 ). Note, that the “ critical function of otoconia and otoliths is to
impart inertial movements in response to gravity or linear acceleration, which
stimulates the underlying sensory hair cells by defl ecting their stereocilia bundles, ”
(Deans et al. 2010 ; see also Hudspeth 2008 ).
There are numerous publications on “earstones”, or otoliths which are defi ned
as “paired calcifi ed structures used for balance and/or hearing in all teleost fi shes,”
(Campana 1999 ; see also Campana 2004 ; Tuset et al. 2003 ). The “chemistry of
water” seems to be the crucial point for the basic pathway of the bulk of inorganic
elements into the crystalline structure like otolith. Gills or intestine are involved
3.3 Otoconia and Otoliths