Migration history of fishes inferred from otolith microchemistry including oxygen isotopic composition and Sr : Ca ratio

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Objectives of this study were to examine fish migratory history from otolith microstructure and microchemistry including oxygen isotopic composition and Sr : Ca ratios. We confirmed that secondary ion mass spectrometry (SIMS) was useful methodology to analyze oxygen isotopes of fish otolith. The changes in water temperature that fish individual experienced is reconstructed by examine oxygen isotopic composition accompanied with otolith daily rings. [Oxygen isotopic composition] Glass eel(Japanese eel)otoliths were used for this oxygen isotopic examination. Each otolith was grounded to expose the otolith core. The smoothing of grounded otolith surface was very critical for the accuracy of SIMS analysis. The oxygen isotopic composition was examined on the otolith including otolith core and surrounding regions. The ratio (^<18>O/^<16>O) was revealed to be higher in ototith core than the other surrounding region, suggesting that spawning temperature of eels was lower than that the larvae exposed. Eels may spawn in deeper waters in their spawning area. [Otolith Sr : Ca ratios] Otolith Sr : Caratios were examined on otoliths of Japanese sardine and ayu (amphidromous fish). Changes in otolithSr : Ca ratios were not accompanied with changes in water temperature and salinity in Japanese sardine, suggesting that otolith Sr : Ca ratio was not useful for investigating the migration history of Japanese sardine. In contrast, the ratio well reconstructed the changes in distribution environment (i.e. sea, brakish, freshwater) in amphidromous ayu individuals. And it was revealed to be useful to distinguishing between amphidromous and non-amphidromous stocked fish.