ABSTRACT. – To test the hypothesis that both otoliths (left and right sagittae) of a flatfish, Solea solea (Linnaeus, 1758), display the same elemental fingerprint information, we analyzed whole-otolith preparations from coastal lagoons and marine sites in the NW Mediterranean for the presence of 15 elements (⁷Li, ²⁴Mg, ²⁷Al, ⁴⁴Ca ⁵²Cr, ⁵⁵Mn, ⁵⁶Fe, ⁵⁹Co, ⁶⁰Ni, ⁶³Cu, ⁶⁸Zn, ⁸⁶Sr, ¹¹¹Cd, ¹³⁷Ba and ²⁰⁸Pb), their ratio to Ca and for carbon and oxygen stable isotope ratios. We found significant concentration differences between the two otoliths for two elements, i.e. ⁷Li (right > left) and ⁸⁶Sr (right > left) all sites pooled together. However, this general trend differed between sites, with coastal lagoons showing significant differences for additional elements between the two otoliths, such as ⁴⁴Ca and ¹³⁷Ba in coastal lagoons for small juveniles, ⁵⁵Mn and ⁶⁸Zn in coastal lagoons for larger juveniles, and for ⁵⁵Mn/⁴⁴Ca for adults in marine sites. Both δ¹⁸O and δ¹³C isotopic ratios were higher in the right than in the left otolith (a difference of ~16% between otoliths in both cases) but these trends were not statistically significant and showed no spatial pattern. The left otolith was significantly heavier than the right otolith, a difference which decreased significantly with increasing fish size. Otolith mass was shown to correlate significantly with the δ¹⁸O and δ¹³C ratios, as well as for concentration in some elements and their ratio to Ca for both otoliths (⁵⁵Mn, ⁶⁸Zn, ⁸⁶Sr and ¹³⁷Ba) and for ²⁷Al on the left otolith only. Our results imply that the two otoliths are not interchangeable for fingerprint analysis. The right vs. left difference for ⁴⁴Ca, ⁸⁶Sr and ¹³⁷Ba decreases with increasing fish size, which suggests that differences in element concentrations may be at least partly driven by fish size. Thus, fish physiology and inner ear functioning may differ between otoliths in intensity and/or type of process as a function of increasing fish size and so possibly explain left vs. right differences in the otoliths of S. solea.