Fractionation of stable carbon (C) isotopes in the essential fatty acids 18:2n-6, 18:3n-3, 20:4n-6, 20:5n-3, and 22:6n-3 was investigated in the zebrafish Danio rerio and the mud snail Bellamya chinensis fed the same two diets. These diets differed in essential fatty acid compositions: (1) TetraMin contained all five fatty acids, and (2) Chlorella contained only two, 18:2n-6 and 18:3n-3. On average, the isotopic fractionation was −0.5 ± 0.9 ‰ for 18:2n-6 and 18:3n-3 for all experiments, indicating that the fractionation of these essential fatty acids was negligible. However, the isotopic fractionation of 20:4n-6, 20:5n-3, and 22:6n-3 varied greatly between species and between diets. The isotopic fractionation of the Chlorella diet was −0.2 and −6.9 ‰ for zebrafish and mud snail, but 4.2 and −1.3 ‰, respectively, when these consumers were fed TetraMin. This variation could be explained by the different amount of assimilation and the biosynthesis of these fatty acids from their precursors (i.e., 18:2n-6 and 18:3n-3). These results indicate that the isotopic composition of C20 and C22 essential fatty acids was strongly influenced by the fatty acid composition in the diets. Thus the stable C isotope ratios of C18 essential fatty acids in consumers are more useful as dietary tracers in food web studies.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics