STABLE CARBON-ISOTOPE RATIOS OF FATTY-ACIDS IN SEAGRASS AND REDHEAD DUCKS

Fatty acids were extracted from roots and rhizomes of the seagrass, Ha lodule wrightii, and from subcutaneous fat tissues of eight redhead du cks (Aythya americana) collected either in Texas or South Dakota. Stab le carbon isotope ratios (delta(13)C) of individual fatty acids were m easured by gas chromatography/combustion/isotope ratio mass spectromet ry (GC/C/IRMS). In cases where individual fatty acids were not complet ely resolved by the chromatographic column, argentation chromatography was used as a pre-separation technique to separate saturated fatty ac ids from unsaturated fatty acids. The majority of fatty acids extracte d from roots and rhizomes of H. wrightii and from subcutaneous fat of redhead ducks had delta(13)C values that clustered about the delta(13) C value measured for the total fatty acid fraction of the parent tissu e. Normal and anteiso isomers of the saturated 17:0 fatty acid had the most negative delta(13)C values in the organisms studied. Texas redhe ad ducks which likely had consumed a diet comprised primarily of roots and rhizomes of H. wrightii for at least 1 month had delta(13)C value s of fatty acids that were more positive than those of the identical f atty acids in the seagrass. This discrepancy in delta(13)C indicates t hat fatty acids in ducks are synthesized from molecules with more posi tive delta(13)C values, such as carbohydrates and/or proteins, rather than by direct incorporation of fatty acids from the diet, or else the re are isotopic fractionations associated with the biosynthesis and ca tabolism of these compounds. (C) 1998 Elsevier Science B.V. All rights reserved.