136
in this transport between the water and the blood plasma of the fi sh. The next step
occurs between the endolymph and the crystallizing otolith. As it was described:
“Water passing over most elements in freshwater fi sh and the continual drinking
of marine fi sh is the main source of waterborne elements for assimilation via the
intestine. Plasma concentrations of Ca are approximately 1/3 of that of marine
waters, but fl ux rates between water and blood are even lower, since only excreted
ions are replaced. In saltwater fi sh, trace elements are probably assimilated from the
intestine in direct proportion to their relative concentration in the water, albeit with
low effi ciency,” (Campana 1999 ; see also Olsson et al. 1998 ).
The detailed mechanism concerning formation of otoconia and how it is subsequently embedded in the otoconial membrane during inner ear development is
still unknown. In contrast to mammals where this process is initiated during embryogenesis and is completed during early postnatal maturation (Lim 1973 ; Erway et al.
1986 ), development of the otolith in Teleostei, also being initiated early in otic
development, proceeds throughout the life of the animal (Whitfi eld et al. 2002 ). It is
thought that the origin of calcium in the endolymph is regulated by the activity of
plasma membrane associated enzyme called Ca
2+ -ATPase isoform 2 (PMCA2) that
is responsible for the extrusion of Ca
2+ from the hair cells (Kozel et al. 1998 ).
Both, molecular structure and composition of fi sh otoliths is excellently represented in the classical paper by Degens and co-workers in 1969. The summary of
this work include some points, which are still correct to this date, thus, I take a liberty
to cite them as follow:
“1. Otoliths are mineralogically composed of aragonite. The aragonite fi brils are
arranged with their long axis roughly perpendicular to the outer margin of the
otoliths. Bands of organic matter intersect the aragonite fi brils transverse to c;
the spacing of the bands narrows towards the center of the otoliths.
2. The interrelationship between organic and inorganic matter indicates that the
aragonite is formed by epitaxial growth on a protein matrix. Metal ions become
coordinated to the oxygen functions displayed on the organic tissue, resulting in
the formation of metal ion coordination polyhedra, and bicarbonate becomes
linked via hydrogen bridges to amino acids. Subsequent exchange of bicarbonate oxygen for metal ion polyhedra oxygen will stabilize the structure and introduce the nucleation of mineral seeds. Inasmuch as Ca
++ O 9 , polyhedra are
involved, the mineral form will be aragonite.
3. The mineralized tissue is a fi brous protein with a molecular weight exceeding
150,000. The amino acid composition is biochemically unique and not affected
by phylogenetic and environmental events. The term otolin is proposed for this
new kind of protein.
4. The variation of total organic matter and the stable isotope distribution in the
aragonite can be used as phylogenetic and environmental criteria to distinguish,
for example, between freshwater and marine species, to determine migratory
tendencies, or to measure the mean temperature at which the fi sh lived.
5. The compositional variation of otoliths in combination with their ultrastructure
suggests that otoliths may function as piezoelectric bodies for the recording of
depth and sound,” (Degens et al. 1969 ; see also Morris and Kittleman 1967 ).
3 Biocomposites and Mineralized Tissues
in this transport between the water and the blood plasma of the fi sh. The next step
occurs between the endolymph and the crystallizing otolith. As it was described:
“Water passing over most elements in freshwater fi sh and the continual drinking
of marine fi sh is the main source of waterborne elements for assimilation via the
intestine. Plasma concentrations of Ca are approximately 1/3 of that of marine
waters, but fl ux rates between water and blood are even lower, since only excreted
ions are replaced. In saltwater fi sh, trace elements are probably assimilated from the
intestine in direct proportion to their relative concentration in the water, albeit with
low effi ciency,” (Campana 1999 ; see also Olsson et al. 1998 ).
The detailed mechanism concerning formation of otoconia and how it is subsequently embedded in the otoconial membrane during inner ear development is
still unknown. In contrast to mammals where this process is initiated during embryogenesis and is completed during early postnatal maturation (Lim 1973 ; Erway et al.
1986 ), development of the otolith in Teleostei, also being initiated early in otic
development, proceeds throughout the life of the animal (Whitfi eld et al. 2002 ). It is
thought that the origin of calcium in the endolymph is regulated by the activity of
plasma membrane associated enzyme called Ca
2+ -ATPase isoform 2 (PMCA2) that
is responsible for the extrusion of Ca
2+ from the hair cells (Kozel et al. 1998 ).
Both, molecular structure and composition of fi sh otoliths is excellently represented in the classical paper by Degens and co-workers in 1969. The summary of
this work include some points, which are still correct to this date, thus, I take a liberty
to cite them as follow:
“1. Otoliths are mineralogically composed of aragonite. The aragonite fi brils are
arranged with their long axis roughly perpendicular to the outer margin of the
otoliths. Bands of organic matter intersect the aragonite fi brils transverse to c;
the spacing of the bands narrows towards the center of the otoliths.
2. The interrelationship between organic and inorganic matter indicates that the
aragonite is formed by epitaxial growth on a protein matrix. Metal ions become
coordinated to the oxygen functions displayed on the organic tissue, resulting in
the formation of metal ion coordination polyhedra, and bicarbonate becomes
linked via hydrogen bridges to amino acids. Subsequent exchange of bicarbonate oxygen for metal ion polyhedra oxygen will stabilize the structure and introduce the nucleation of mineral seeds. Inasmuch as Ca
++ O 9 , polyhedra are
involved, the mineral form will be aragonite.
3. The mineralized tissue is a fi brous protein with a molecular weight exceeding
150,000. The amino acid composition is biochemically unique and not affected
by phylogenetic and environmental events. The term otolin is proposed for this
new kind of protein.
4. The variation of total organic matter and the stable isotope distribution in the
aragonite can be used as phylogenetic and environmental criteria to distinguish,
for example, between freshwater and marine species, to determine migratory
tendencies, or to measure the mean temperature at which the fi sh lived.
5. The compositional variation of otoliths in combination with their ultrastructure
suggests that otoliths may function as piezoelectric bodies for the recording of
depth and sound,” (Degens et al. 1969 ; see also Morris and Kittleman 1967 ).
3 Biocomposites and Mineralized Tissues