文摘
Fish scales may be used as nonlethal alternative structures to otoliths for establishing chemical time-series that trace migration and habitat use for euryhaline species such as Atlantic tarpon (Megalops atlanticus). We survey four decades of fish scale studies employing elemental analyses to show the wide diversity of aims, approaches and instrumentation. Analyses are mainly solution-based measurements of whole or subsampled scales or in situ solid-sampling techniques of specific growth regions. Although spot-based transects across scales have been employed for a handful of species, continuous elemental transects across scale growth increments are rare. Laser ablation based sampling methods that assay scale exteriors can be difficult to implement for species with natural topographic variations exceeding the focal range of the laser. These limitations may be overcome by performing laser ablation of scales in cross-section when scale thickness in the well-calcified external layer provides enough surface area for a laser transect. For this study, scales of Atlantic tarpon were embedded in epoxy and longitudinally cross-sectioned to expose the scale growth record of the external layer. Laser ablation ICP-MS was used to quantify continuous profiles of element:Ca ratios across scale growth increments. The analytes surveyed (Mg, P, Ca, Mn, Sr, and Ba) were consistently above the limits of detection (LODs) across each scale with the exception of Pb for one scale. Obtaining high resolution elemental life history profiles from scales will be essential for future efforts to use this structure as a non-lethal substitute for otoliths in Atlantic tarpon and other migratory fishes that possess scales with sufficiently thick calcified external layers to permit a cross-sectional approach. Keywords Atlantic tarpon Scales Otoliths ICP-MS Laser ablation