Advances in laser ablation analysis of fish hardparts

Strontium isotope ratios (87Sr/86Sr) in otoliths are a well-established tool to determine origins and movement patterns of fish. However, otolith extraction requires sacrificing fish, and when working with protected or endangered species the use non-lethal samples such as scales, spines, and fin rays, is preferred. Unlike otoliths that are predominantly aragonite, these tissues are comprised of biological apatite. Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analysis of biological apatite can induce significant interference on mass 87, causing inaccurate 87Sr/86Sr measurements. To quantify this interference, we applied LA-MC-ICP-MS to three marine samples (white seabass, Atroctoscion nobilis, otolith; green sturgeon, Acipenser medirostris, pectoral fin ray; salmon shark, Lamna distropis, tooth) and freshwater walleye (Sander vitreus) otoliths, scales, and spines. Instrument conditions that maximize signal intensity resulted in elevated 87Sr/86Sr isotope ratios in the bioapatite samples, related to a polyatomic interference (40Ca31P16O,40Ar31P16O). Retuning instrument conditions to reduce oxide levels removed this interference, resulting in accurate 87Sr/86Sr ratios across all tissue samples. This method provides a novel, non-lethal alternative to otolith analysis to reconstruct fish life histories.