Using Mg as a Proxy for Crystal Structure and Sr as an Indicator of Marine Growth in Vaterite and Aragonite Otoliths of Aquaculture Rainbow Trout

Abstract

Otoliths of rainbow trout Oncorhynchus mykiss reared in marine cages were analyzed by laser ablation-inductively coupled plasma mass spectrometry to determine their Sr and Mg concentrations and by micro-Raman spectrometry to assess mineralogy. Analyses of transects from the core of the otolith to the growing edge (incorporating otolith material produced during freshwater hatchery and marine cage growth) revealed that these transects were composed of aragonite, vaterite, or both. The concentration of Sr varied significantly between mineral polymorphs and environments (hatchery or marine). In vaterite transects, Sr concentrations increased an average of 130 lg/g between freshwater hatchery growth and marine growth. This increase represents a near doubling of the Sr concentration in vaterite and made Sr a suitable indicator of a change in the environment as reflected in vaterite transects. In aragonite transects, Sr concentrations increased an average of 1,330 lg/g between hatchery and marine growth, which simplified the identification of the timing of marine transfer. The concentrations of Mg also varied significantly between mineral polymorphs, the difference in the average concentration between aragonite and vaterite being 1,179 lg/g. This allowed for the use of Mg as a proxy for mineralogy. While there was an increase in Mg concentration between hatchery and marine growth in some vaterite otoliths, the change was small compared with the change as a result of mineralogy. The average aragonite-vaterite partition coefficients were 5.238 and 8.096 for Sr and 0.057 and 0.128 for Mg for hatchery and marine growth, respectively.

Asteriscus v. lapillus: comparing the chemistry of two otolith types and their ability to delineate riverine populations of common carp Cyprinus carpio

“…Striking differences were observed in the chemistry of C. carpio asteriscus and lapillus otoliths analysed during this study. Building on previous work investigating the chemical composition of these polymorphs in other freshwater and marine species (Gauldie, 1996;Chesney et al, 1998;Brown & Severin, 1999;Tomás & Geffen, 2003;Melancon et al, 2005;Veinott et al, 2009), this study has demonstrated concomitant enrichment in Mg and Mn in the vateritic asteriscus and depletion in the aragonitic lapillus, and additionally, elevated Sr and Ba concentrations in lapilli coinciding with very low Sr and Ba values in asterisci. No differences in 87 Sr: 86 Sr values were apparent between the two otolith types, which is not unexpected as the relative uptake of 87 Sr and 86 Sr into otoliths is thought to be unaffected by physiological and biochemical mechanisms (Kennedy et al, 2000).…”

“…Although the otoliths of most fishes are composed of aragonite, several species exhibit polymorphic sagittae, most often characterized by vateritic inclusions within a predominately aragonitic matrix (Gauldie, 1993). This phenomenon has been observed in Chinook salmon Oncorhynchus tshawytscha (Walbaum 1792) (Gauldie, 1986(Gauldie, , 1996, inconnu Stenodus leucichthys (Güldenstädt 1772) (Brown & Severin, 1999), Atlantic herring Clupea harengus L. 1758 (Tomás & Geffen, 2003), lake trout Salvelinus namaycush (Walbaum 1792) (Melancon et al, 2005), European eels Anguilla anguilla (L. 1758) (Tzeng et al, 2007) and rainbow trout Oncorhynchus mykiss (Walbaum 1792) (Veinott et al, 2009) among others. Some species' otoliths, including asterisci of cyprinids, are composed entirely of vaterite (Escot & Granado-Lorencio, 1998;Lenaz et al, 2006;Gao et al, 2009;Li et al, 2009;Yang et al, 2009).…”

“…Biomineralization of these polymorphs may be physiologically (Gauldie, 1993;Bowen et al, 1999) or genetically (Gauldie, 1993;Brown & Severin, 1999;Söllner et al, 2003) controlled and related to spatially non-uniform protein and chemical gradients in the surrounding endolymph (Payan et al, 1999). Previous studies have consistently reported depleted Sr, Na and Ba concentrations and enriched Mg and Mn levels in vateritic otolith sections compared with aragonitic sections in individual fishes (Mugiya & Tanaka, 1995;Gauldie, 1996;Melancon et al, 2005Melancon et al, , 2009Lenaz et al, 2006;Tzeng et al, 2007;Veinott et al, 2009). A commonly advanced explanation for these findings is preferential uptake of larger cations like Sr 2+ and Ba 2+ into aragonite in replacement of Ca 2+ ions, and a reduced capacity of vaterite to incorporate these ions (Brown & Severin, 1999;Tomás & Geffen, 2003;Melancon et al, 2005).…”

Identification of Bighead Carp and Silver Carp early-life environments and inferring Lock and Dam 19 passage in the Upper Mississippi River: insights from otolith chemistry

“…Concentrations of strontium, barium, and magnesium were converted to molar element:calcium ratios (Sr:Ca, Ba:Ca, or Mg:Ca; lmol/mol) using calcium as an internal standard and the stoichiometric concentration of calcium in aragonite (400,436 lg Ca g -1 CaCO 3 ). Molar Mg:Ca ratio was used in conjunction with Ba:Ca and Sr:Ca data as an indicator of the potential presence of vaterite (a crystalline form of CaCO 3 that differs in affinity for Mg, Ba, and Sr compared to aragonite; Melancon et al 2005;Veinott et al 2009) in otolith samples. Otolith Mg:Ca [ 400 lmol/mol in combination with Sr:Ca \ 100 lmol/mol and Ba:Ca \ 4 lmol/mol was considered indicative of the potential presence of vaterite.…”

Sturgeon and paddlefish (Acipenseridae) sagittal otoliths are composed of the calcium carbonate polymorphs vaterite and calcite

“…Determination of the CaCO 3 polymorph composition of otoliths has important implications for studies of otolith microchemistry, a technique that quantifies the elemental fingerprints in otoliths incorporated from water chemistry to reconstruct individual environmental history. Previous studies have reported differences in elemental concentrations between or among polymorphs using laser‐ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS; Melancon et al , ; Tzeng et al , ; Veinott et al , ). Because these studies, however, were unable to take newly discovered differences in polymorph densities into account during data post‐processing (Wang & Becker, ; Demichelis et al , , ), conclusions regarding differences in elemental concentrations among polymorphs must be re‐examined.…”