抄録
Trace element concentration in fish otoliths was analyzed by particle induced X-ray emission (PIXE). Otoliths were collected from juvenile red sea bream, Pagrus major, in accordance with their growth stage from 19 days after hatching to 106 days. Individuals were reared in three different sea-farming stations: Momoshimaand Hakatajima stations located along the western Seto Inland Sea and Miyazu station along the western coast of the Sea of Japan. Seawater temperatures were continuously measured using micro-data logger type thermometers at 1.5 m depth fromJune to August 1993 in aquaculture basins during fish rearing periods at 20-minute or one hour intervals. Fluctuations of temperature at the three stations showed different positive thermal gradients and different mean temperatures from the beginning to the end of the experiment. Otolith surfaces without cutting or polishing werethen exposed in air to a 1.16 MeV proton beam. X-ray spectra detectedwith a lithium-drift silicon Si(Li) detector indicated that reared fish tolithscontained some trace elements of 2+ valence such as Mn (40-64 ppm), Fe (169-246 ppm), Zn (61-120 ppm), and Sr (1634-2330 ppm). We ascertained that trace elementsin the surface of otoliths can be detected accurately to several tens ppm by using PIXE. Concentrations of these trace elements appear to increase in proportionto temperature.
