A Case Study of Coilia nasus: Is There a Difference in Microchemical Signatures Between Left and Right Fish Sagittae?

Owing to the asynchronous deposition of trace elements between paired left and right otoliths within individual fish, researchers must consciously and uniformly use only single otoliths (especially the left one) for microchemical studies. To ensure reliability of unilateral otolith data for inferring the same habitat experiences of individual fish, this study focused on Coilia nasus as a representative case to validate whether the microchemical composition was consistent between left and right sagittal otoliths. Electron probe microanalysis was employed to determine microchemical profiles of Sr and Ca in both otoliths of 20 wild C. nasus specimens of the same age. At the individual level, Sr/Ca ratios in corresponding micro-regions (e.g., core and edge) of bilateral otoliths showed highly significant positive correlations, with approximately 92.59% of paired comparisons showing no significant differences at equivalent life-history stages, demonstrating that microchemical signals recorded by either otolith are highly consistent in both spatial distribution and elemental concentration levels. This study provides evidence of fundamental concordance in microchemical composition between bilateral otoliths within an individual, providing critical references on the methodological foundation for reliably using either the left or right otolith in future studies on otolith microchemistry of fish population connectivity, migration characteristics, and life history reconstruction.