Abstract
The effects of rapid changes in salinity and temperature on the elemental composition of sagittal otoliths taken from the juvenile Japanese flounder, Paralichthys olivaceus, were studied using a particle induced X-ray emission (PIXE) technique. Four elements were detected in the otoliths; Ca, Mn, Zn and Sr. Seven days' exposure to low salinity (transfer from 100% to 50% sea water) caused an increase in Sr and a decrease in Zn of the otoliths, while no significant changes were found in Ca and Mn. Thirty and 60 days' exposure to 50% sea water caused a decrease in Sr and a slight increase in Zn and Mn. A rapid drop in culture temperature (transfer from 20°C to 15°C) caused a remarkable increase in Sr concentration in the otoliths on day 7. Zinc concentration also decreased significantly. Thirty and 60 days after the exposure, Sr was slightly higher than that of the control. No significant differences were found in the concentrations of Zn and Mn between the control and the low temperature groups, while Zn decreased slightly 30 and 60 days after the exposure. A similar relationship was also found in each element to the Ca ratio of the otoliths. It was thought that the ratios of Sr and Zn concentrations to Ca in fish otoliths were effective indices (information sources) for predicting the history of environmental conditions experienced by a fish in the past. However, these results also suggest that the physiological fluctuations triggered by radical changes in environmental conditions seriously affect not only the reabsorption rate but also the incorporation rate of various elements into the otoliths in direct or indirect ways. Therefore, effects of the changes in various environmental factors on physiological conditions of fish must be carefully considered for the interpretation of otolith element data.
