Comparison of solution-based versus laser ablation inductively coupled plasma mass spectrometry for analysis of larval fish otolith microelemental composition

Otolith microchemistry has become a widely used tool for fisheries-based research in marine systems. However, its application to systems without well-defined juvenile nursery areas in which distinct otolith elemental signatures can develop (i.e., most freshwater systems) remains limited. In large part, this deficiency is due to unsuitable protocols for reliably processing and analyzing small otoliths of larvae. Herein, we evaluate the abilities of solution-based (SO) and laser ablation (LA) inductively coupled plasma mass spectrometry (ICPMS) to quantify the otolith elemental composition of larval yellow perch Perca flavescens captured in three distinct spawning locations in Lake Erie (USA-Canada). Analysis of otolith pairs by each technique demonstrated that both SO- and LA-ICPMS could be used to reliably quantify the more abundant elements, such as Sr and Ba. Magnesium and zinc, analyzed by use of both SO- and LA-ICPMS, also met the criteria for inclusion in our analyses (i.e., the coefficients of variation of standards were <10.5%, and over 90% of samples were above detection limits at a single location). Upon closer inspection of the data, however, we found that estimates of Mg and Zn were only reliable for LA-ICPMS. Estimates of these two elements using SO-ICPMS were unrealistically high, probably owing to contamination during the otolith dissolution and handling phases. We also found that LA-ICPMS provided more precise estimates than did SO-ICPMS for nearly all elements explored, but LA-ICPMS was somewhat limited by high limits of detection for some elements. Despite these differences, both techniques could accurately discriminate among larvae produced in different Lake Erie spawning locations, primarily because of the significant variation in Sr among larval otoliths. Ultimately, although both methods are appropriate for analysis of otoliths from larvae, we recommend the use of LA-ICPMS in future otolith microchemical applications involving larvae.