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Experimental Evaluation of Stable Isotope Fractionation in Fish Muscle and Otoliths
Citation:
Elsdon, T. S., S. AYVAZIAN, K. W. McMahon, AND S. E. Thorrold. Experimental Evaluation of Stable Isotope Fractionation in Fish Muscle and Otoliths. MARINE ECOLOGY PROGRESS SERIES. Inter-Research, Luhe, Germany, 408:195-205, (2010).
Impact/Purpose:
The research was directed at resolving issues of the use of stable isotopes to determine diet and trophic positions of fish using both muscle tissue and otoliths in a controlled laboratory setting.
Description:
We investigated an unresolved question in the use of stable isotopes to determine diet and trophic position of fish using both muscle and otoliths. We determined: i) the degree of fractionation of δ13C and δ15N between diet and muscle, and assessed if fractionation was consistent among fish fed on different diets, ii) the effect of extracting lipids from fish muscle on the fractionation between diet and muscle, their relative position, and the variance associated with groups, and iii) fractionation of δ13C between otolith and diet, and otolith and muscle. Carbon and nitrogen both fractionated from diet to fish muscle, with differences detected among diets. Carbon fractionation from diet to fish muscle exceeded assumed values of < 1‰ and ranged from 0.62 to 2.96‰, while nitrogen fractionation ranged from 2.66 to 7.83‰. Extracting lipids from fish muscle enriched both δ13C and δ15N, with enrichment being approximately 1‰. Lipid extraction did increase variation in treatment means for δ15N, but not δ13C; however, the relative placements of treatment groups with respect to each other and their diets were reasonably unaltered. Otoliths were enriched in δ13C compared to both diet and fish muscle. Fractionation from diet to otolith was similar among dietary treatments, with a strong positive correlation (r2 = 0.904) occurring between the two, suggesting that otolith δ13C does reflect diet. The results provide a clearer understanding of isotope fractionation, sample treatment, and the potential use of otoliths as dietary indicators.
