EFFECTS OF SALINITY AND ONTOGENIC MOVEMENTS ON STRONTIUM-CALCIUM RATIOS IN THE OTOLITHS OF THE JAPANESE EEL, ANGUILLA-JAPONICA TEMMINCK ANDSCHLEGEL

To study the mechanism of Sr incorporation into otoliths of the Japane se eel, Anguilla japonica, a total of 100 elvers collected from an est uary were reared in the laboratory at salinities of 0, 20, 25 and 35 p arts per thousand for approximately seven months. The elvers grew from 56 mm TL to 100-300 mm TL. Twenty elvers were randomly selected and t he Ca and Sr concentrations of their otoliths were analyzed from the p rimordium to the edge, using an electron microprobe equipped with a fo ur-channel wavelength-dispersive spectrometer. Sr/Ca ratios in the oto liths of eels reared in various salinities were much lower than the ra tio of 15 x 10(-3) observed in elvers about one month before they arri ved at the estuary. The irreversibility of Sr/Ca ratios at 35 parts pe r thousand salinity in this experiment indicated that the drastic chan ge of the Sr/Ca ratios in otoliths of elvers was not due to the reduct ion of salinity in the coastal waters, but more likely to the developm ent from leptocephalus to glass eel. The mean Sr/Ca ratios in the new increments of the otoliths of eels during the rearing period were high ly correlated with salinity (S), [Sr/Ca] x 10(3) = 3.797 + 0.14S (n = 20, r = 0.77), which can be used to predict elver movements and habita t utilization rates.