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Abstract

Fish otoliths are calcium carbonate aggregates in the membranous labyrinth of
all teleost fishes. The deposition of these structures is affected by both physiological
and environmental factors which can cause changes in both the rate of otolith
depositon and in the composition of the material deposited. The rate of otolith
deposition, particularly in regard to the alternation of calcium carbonate-rich and
protein-rich zones, has been widely investigated in an attempt to understand processes
of ageing and growth in fishes. Aspects of the chemistry of these structures,
particularly trace elements and stable isotopes, that may vary in response to
physiological and environmental change, have not been studied in detail and are the
basis of this research.
The effects of temperature, somatic growth, otolith growth, condition factor,
RNA/DNA ratio, age and season on the incorporation of Sr, Na, K and S into the
sagittal otoliths of Australian salmon and blue grenadier were investigated by a
combination of laboratory rearing experiments and monthly collections of wild fish.
Microchemical analyses of otolith chemistry were carried out with a wavelength
dispersive electron microprobe. There were significant differences in otolith Sr/Ca
ratios among Australian salmon maintained in the laboratory at different temperatures
and a slight positive correlation with temperature, but there was no evidence for a
linear relationship between Sr/Ca ratio and temperature. Biologically significant
relationships between other factors were not evident in laboratory-maintained fish.
Furthermore, the variability of elemental ratios within temperature treatments and
within individual otoliths was very significant. There were highly significant
correlations between otolith chemistry and fish age in wild blue grenadier and it was
hypothesized that the seasonal and age-related variation in otolith Sr content is largely
the result of changes in the proportions of free and bound Ca and Sr present in the
blood plasma and that this is in turn a function of the quantity and type of proteins
present in the plasma. Data on the level of Sr present in the saccular endolymph and
the sagittae of 12 fish species showed that there was a very strong relationship
between the composition of the endolymph and the otoliths.
Seasonal collections of otoliths, blood plasma, saccular endolymph and
biological data from Pseudophycis barbatus indicated that physiology was largely
responsible for changes in endolymph composition. Measurements of weight,
length, gonad weight, and Sr, Ca, Na, K, protein, triglyceride, phosphate and
glucose in the plasma and endolymph were used to develop multivariate models to
explain endolymph and otolith composition. It was possible to explain up to 98% of
the variance in the endolymph Sr content of female Pseudophycis barbatus. The
range of otolith Na and K content could be estimated using models in the geochemical
literature. These results showed that otolith trace element composition was based on
the interaction of physiological, ecological and environmental factors.
Life-history transects of otolith microchemistry in a range of species indicated that the factors that ultimately effect otolith composition are generally not under strong
environmental control. However, it was found that variations in otolith
microchemistry can be useful in studies aimed at determining distributional
relationships among contemporaneous individuals, particularly in studies seeking to
identify nursery grounds or where there is an interest in fine resolution "stock"
discrimination. Recognizable "signatures" in otolith life-history transects may result
when co-occurring individuals experience extreme environmental conditions. In most
species there appears to be little information that can be gained directly from the
interpretation of otolith Sr/Ca, Na/Ca, K/Ca and S/Ca ratios. The complex interaction
of factors affecting trace element levels in fish otoliths makes it virtually impossible to
determine those factors which result in a particular quantity of Sr, Na, K or S in an
otolith or, to use these elements as indicators of physiological or environmental
change.
Otolith microchemistry of anadromous and nonanadromous salmonids was
investigated to determine if there were differences among migratory and nonmigratory
individuals and to determine if the habitat where vitellogenesis took place would affect
the composition of the otolith primordia of the progeny. There were significant
differences in otolith Sr/Ca ratios among adult anadromous and nonanadromous
salmonids and the otolith Sr/Ca ratios in the primordia were greater in the progeny of
anadromous salmonids than in the otolith primordia of the progeny of
nonanadromous individuals.
Studies of oxygen and carbon isotopes in the otoliths of laboratory maintained
Arripis trutta showed that oxygen isotopes were deposited near to equilibrium with
seawater and, contrary to evidence presented in the literature, can be used to predict
environmental temperatures. Approximately 30% of the otolith carbon was from
metabolically derived sources. Oxygen isotopes in otoliths from a wide range of fish
species were found to be deposited in equilibrium with seawater, while there are
varying levels of carbon isotope disequilibria. The hypothesis that the magnitude of
carbon isotope disequilibria is related to metabolic rate (V02 ) was developed and
evidence in support of this hypothesis was presented.
Scanning and transmission electron microscope studies of fish otoliths showed
the relationship between organic and inorganic material in microincrements and
presented evidence for the complete cessation of calcium carbonate deposition during
periods of stress. Ultrastructural observations showed that aragonite crystals in fish
otoliths are highly variable in morphology and size and, thus, may be an important
factor in determining within otolith variations in trace element chemistry.

Item Type:	Thesis - PhD
Authors/Creators:	Kalish, John M
Keywords:	Otoliths, Fishes, Fishes
Copyright Holders:	The Author
Copyright Information:	Copyright 1989 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Journal article in pocket at back of volume. Includes bibliographical references (p. 303-339). Thesis (PhD)--University of Tasmania, 1991
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