Abstract
Otolith marking provides a reference point for otolith growth patterns by validating the temporal significance of growth increments. This widespread method is primarily implemented using fluorescent dyes. The incorporation of a trace element that appears naturally in otoliths offers an alternative approach. Diplodus annularis and Serranus scriba otoliths were marked with an intramuscular injection of SrCl 2 diluted in 0.9% sterile saline solution (55 mg Sr ml -1 saline solution), given at a dose of 100 mg Sr kg -1 fish. At 277 to 366 days after marking, the fishes showed little or no mortality and experienced growth in length and weight. All of the otoliths analyzed showed a clear Sr mark detected with backscattered or secondary electron imaging during a scanning electron microsope (SEM) analysis. The mark was confirmed by Sr analysis using an X-ray detector and an energy dispersive spectrometer system with the SEM. The otoliths continued to grow after the mark, and background Sr values in this new growth were much lower than at the mark. This method was feasible and yielded good results. However, the method’s cost may limit its applicability to experimental studies.
Highlights
The marking and tagging of individuals is a widespread practice in population dynamics and age validation studies (Wright et al 2002)
Diplodus annularis and Serranus scriba otoliths were marked with an intramuscular injection of SrCl2 diluted in 0.9% sterile saline solution (55 mg Sr ml-1 saline solution), given at a dose of 100 mg Sr kg-1 fish
The mark was confirmed by Sr analysis using an X-ray detector and an energy dispersive spectrometer system with the scanning electron microsope (SEM)
Summary
The marking and tagging of individuals is a widespread practice in population dynamics and age validation studies (Wright et al 2002). Since the 1960s, several markers have been used that emit a specific coloured fluorescence under ultraviolet light (e.g. tetracyclines, orange xylenol and alizarin). Some of these markers may have usage restrictions or may demonstrate limited success (Wright et al 2002, Morales-Nin et al 2011 and citations therein). MORALES-NIN et al. Strontium (Sr) isotopes can substitute calcium (Ca) in the mineralized portion of the otolith, with Sr concentrations proportional to environmental availability and conditions (Campana 1999). The elemental otolith signatures, of Sr, are used as natural tags to distinguish between wild and reared fish (Gibson et al 2010) or to distinguish riverine origins (Kennedy et al 2000). Sr offers a means for marking calcified tissues using a naturally occurring element
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