Japanese eel(Anguilla japonica)larvae were collected from the Jingjiang Section in the lower reaches of the Yangtze River from January to April of 2012.The concentrations of fourteen elements were measured using synchrotron radiation X-ray fluorescence(SRXRF) to analyze the characteristics of otolith microchemistry in early life phase of the eels in ocean and freshwater.The results showed that Ca and Sr were macroelements in otolith.The contents of other elements ranged from 1 to 10 μg/g(such as Sr,Ba,Fe,Mn and Zn),or were below 1μg/g(such as Cr,Ni,Se,Co,Cu and Au).Ni,Cu,Mn,Cr,Co,Zn and Sr were relatively stable in content and the coefficients of variation(CV) were less than 30%.While Se,Au,Ba and Fe were low and extremely unstable(CV= 40.8%-75.0%).Kruskal-Wallis analysis indicated that the content of Fe significantly varied among individuals(P=0.007<0.05).For eels in seawater life stage,Mn,Se,Co and Ba were highly enriched,and BCF_f was higher than 1 000; whilst Sr,Fe,Zn,Ni and Cu were moderately enriched(100< BCF_a-e <1 000).Except for Sr,Ba and Se,there were no significant differences in enrichment coefficients of otolith between yolksac phase and leptocephalus life phases(P>0.05).For eels in freshwater life stage,Sr and Co were highly enriched(BCF_f >1 000),while Se,Zn,Cu,Ba and Mn were moderately enriched,under which circumstance,BCF_f ranged from 100 to 1 000.In addition,Ni and Fe were slightly enriched(10 < BCF_a-e <100).Compared with seawater life stage,the enrichment of Fe,Ba,Mn,Se,Co and Ni in otolith drastically decreased in freshwater.These results indicate that Sr,Ba,Ni and Co are highly responsive to environmental conditions,while Fe and Mn are rarely responsive,and Zn,Cu and Se are negatively responsive.Because environmental high response elements required time lag to pass through physiological barriers before being incorporated into otoliths during migration from seawater to freshwater and because the contents of environmental weak response and negative response elements fluctuated greatly and lacked regular rules to respond to environmental conditions changes,we propose that the following characteristics could be used as the element indicator to reflect fish's migratory behaviors or monitor environmental hydrochemistry:high enrichments in otoliths,weak time-lag responsive to environmental changes,high concentration gradient between different water environment,stability of content and non-essentials and so on.Obviously,Sr and Ba conform to these conditions and could be used as the indicator elements.