Time lag of the response on the otolith strontium/calcium ratios of the Japanese eel, Anguilla japonica to changes in strontium/calcium ratios of ambient water Kazuki Yokouchi & Nobuto Fukuda & Kotaro Shirai & Jun Aoyama & Françoise Daverat & Katsumi Tsukamoto Received: 5 January 2011 /Accepted: 18 May 2011 /Published online: 14 June 2011 # Springer Science+Business Media B.V. 2011 Abstract We conducted a laboratory experiment to validate the relationship between the otolith strontium/ calcium (Sr/Ca) ratio of Japanese eels (Anguilla japonica) and water Sr/Ca ratio when the ratio in water was changed. A linear and additive mixed modeling approach was used to assess otolith Sr/Ca ratio for elver-juvenile Japanese eels when ambient water was changed from seawater to freshwater. There was a significant difference between otolith Sr/Ca ratios of eels reared in freshwater and in seawater (freshwater: 1.3–2.3; seawater: 7.0–7.8 mmol/mol). The response of otolith Sr/Ca ratios of eels was not detected until after 10 d and models suggested that it might not be completed until at least 30–60 d. This study indicated the detailed ability of otolith Sr/Ca ratio to be used as a proxy for reconstructing the individual environmental history of Japanese eels. These findings can provide some assurances for future otolith Sr/Ca studies of eels in this system or in other areas that have similar environ- mental conditions. Keywords Additive mixed model . Otolith microchemistry . Response time . Sr / Ca ratio Introduction Otolith microchemistry has provided detailed esti- mates of individual chronologies of habitat use that are of great value to ecological studies (Campana and Thorrold 2001; Elsdon et al. 2008). In fishes that traverse estuarine salinity gradients during their life history such as diadromous fishes, measurements of strontium/calcium (Sr/Ca) ratios in otoliths have been widely used to infer their life history periods spent in fresh, brackish and marine environments. The Japanese eel, Anguilla japonica, is a catadro- mous fish that spawns in waters west of the Mariana Islands and their larvae migrate back to their freshwater and estuarine growth habitats in Taiwan, eastern China, Korea and Japan (Tsukamoto 1992, 2006, 2009). They spend most of their life for 5–15 years during their growth-phase as “yellow eels”, then they metamorphose into silver eels and they move back downstream to the ocean and begin their migration to the spawning area Environ Biol Fish (2011) 92:469–478 DOI 10.1007/s10641-011-9864-5 K. Yokouchi (*) : N. Fukuda : J. Aoyama : K. Tsukamoto Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277–8564, Japan e-mail: kazukiy@aori.u-tokyo.ac.jp e-mail: kazuki.yokouchi@cemagref.fr K. Yokouchi : F. Daverat Estuarine Ecosystems and Diadromous Fish Research Unit, Cemagref, 50 avenue de Verdun, F–33612 Cestas Cedex, France K. Shirai Department of Earth and Planetary Science, The University of Tokyo, Tokyo 113–0033, Japan