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Australian salmon, Arripis trutta, collected from the east coast of Tasmania, Australia, in 1987, were weighed and measured and their otoliths marked by immersing fish in an oxytetracycline hydrochloride/seawater solution before placement in constant-temperature aquaria. Individual somatic and otolith growth rates were determined for input into mass balance models. Mass balance models were used to determine the oxygen and carbon isotopic composition of otolith material produced during captivity. There was a significant relationship between filsO measured in the otolith aragonite and ambient temperature (r 2 = 0.77). The linear relationship between these data, where 6180 = 6.69 -0.326 (T, °C), was not significantly different from a relationship indicative of equilibrium deposition of oxygen isotopes in aragonite. Otolith carbon was significantly depleted in 13C relative to equilibrium deposition, with depletions > 6.0%o at all temperatures. There was no relationship between 6~3C and temperature. It was estimated that > 30% of the otolith carbon was from metabolically derived sources. Significant differences in otolith carbon isotopes among wild juvenile Australian salmon were hypothesised to be attributable to differences in diet. Levels of variability for both oxygen and carbon isotopes in laboratory-maintained and wild fish were similar to that found by other researchers for foraminifera and these results highlight the importance of large sample sizes when estimating environmental temperatures from oxygen isotopes measured in fish otoliths.

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ABSTRACT. Seasonal variation in the chemistry of bearded rock cod Pseudophycis barbatus plasma. endolymph and otoliths was investigated to determine the effects of physiology and environment on the trace element composition of otoliths. Cod blood, endolymph and otoliths were collected from freshly caught fish at sea. Quantities of protein, triglycerides, phosphate, glucose, calcium, sodium, potassium and strontium were determined in the blood plasma and the endolymph. These data, in conjunction with temperature data and basic biological information such as length, weight, sex, gonad weight, condition and age, were used to explain the levels of Sr found in cod otoliths. Using multiple regression models, it was possible to explain u p to 98.5 % of the total variance in female endolymph Sr levels on the basis of basic biological data and data on blood plasma chemistry. The results indicated that temperature does not directly affect the Sr, Na, K or S content of otoliths but, in adults, that changes in temperature are associated with major physiological changes, specifically the development of the gonads. These seasonal physiological changes are associated with changes in the chemistry of the blood plasma and the endolymph, which can result in differences in the trace element composition of otolith material. A brief investigation of the variability in the relative protein composition of the plasma indicated that there are large intraspecific and seasonal variations In protein complement, notably the albumins and globulins. These changes may ultimately affect the composition of endolymph and otoliths due to differences in metal-binding capacity. This is an area of potential further investigation. Data presented here show that the interpretation of otolith microchemistry data cannot be based on temperature data alone and that variations in otolith chemistry are due to the interaction of numerous factors. In the case of bearded rock cod, the negative correlation between temperature and otolith Sr is a fortuitous one, with changes in physiology being the major force. In other species changes in physiology similar to those observed here are likely to occur at very different times of the year Therefore, before the interpretation of otolith microchemistry data is undertaken, the researcher must carefully consider the various environmental and physiological factors unique to each species.