DRASTIC CHANGES IN OTOLITH STRONTIUM/CALCIUM RATIOS IN LEPTOCEPHALI AND GLASS EELS OF JAPANESE EEL ANGUILLA-JAPONICA

Strontium (Sr) and calcium (Ca) contents and Sr/Ca ratios in otoliths of Japanese eel Anguilla japonica leptocephali and glass eels were examined. The Ca content was almost constant throughout the otoliths, except for the core, in which it was lower. Both Sr content and Sr/Ca ratios increased with age during the leptocephalus stage, but dramatically decreased at age 90 to 100 d. The otolith increment width also showed marked variation at ages 80 to 110 d, indicating the period of metamorphosis. These suggest that the changes in Sr content and Sr/Ca ratios are associated with metamorphosis. X-ray intensity maps revealed that the Sr content in glass eel otoliths increased for short periods at ages of about 20, 50 and 90 d. Such changes seem to be related to events, such as beginning of vertical migration or differing current influences, occurring during the oceanic migration of Japanese eel leptocephali.