Fish otolith trace element maps: new approaches with synchrotron microbeam x‐ray fluorescence

Abstract

Otoliths, the carbonate earstones of fishes, take up minor and trace amounts of elements as they accrete through a fish's life. We apply synchrotron microbeam x-ray fluorescence methods to establish a breakthrough in high-resolution, simultaneous area mapping of multiple trace elements in otoliths, with spatial resolution down to 20 µm and trace element detection down into the part per million range for multiple elements. Concentration maps of Ca, Sr, Zn and, for the first time, Ba, Mn, and Se are obtained simultaneously. Combinations of these elemental maps provide new insights into the environmental history of fishes and their lifetime movements, illustrated by several case studies. This method helps pave the way toward improved spatial analysis of otolith microchemistry.

Selenium detected in fish otoliths: a novel tracer for a polluted lake?

“…Additionally, three fish (one Gizzard Shad, one Atlantic Salmon [Salmo salar], and one Walleye) were collected from Oneida Lake, and their otoliths were similarly extracted. We note that results from two of these species-Walleye and Channel Catfish-were previously presented in a paper describing development of the SXFM method (Limburg et al 2007), and hence in this current study we are adding replication. Fish tissues (muscle, liver, and ovaries if available) and a benthic sample composed of sediment and zebra mussels, all collected from Onondaga Lake, were analyzed for Se and Hg by neutron activation analysis at the University of Missouri-Columbia Research Reactor Center.…”

“…For the past few years, we have been experimenting with the use of synchrotron-based scanning X-ray fluorescence microscopy (SXFM) to map out trace elements in thin sections of otoliths (Limburg et al 2007). This non-destructive method, using monocapillary optics to produce incident x-ray beams at the micro scale, can detect multiple elements simultaneously at levels as low as femtograms/μm 2 under ideal conditions (Bilderback et al 2003).…”

Where do elements bind within the otoliths of fish?

“…Elements with Ca-like properties may become bound to Ca-binding proteins, albeit at considerably lower affinities. This is indirectly supported by the heterogeneous incorporation of some elements in otoliths to protein-rich growth increments (refer to otolith element maps in Arai et al 2003;Limburg et al 2007;McGowan et al 2014).…”

Bromine patterns in Norwegian coastal Cod otoliths—a possible marker for distinguishing stocks?

“…We have mapped concentrations of a number of different elements, sometimes down to sub-ppm levels, in several fish species using scanning x-ray fluorescence microscopy (SXFM, Limburg et al 2007). Our mapping creates 2-dimensional (2-D) displays of spatial configurations of detectable elements ( Fig.…”