Fatty Acid Ratios in Freshwater Fish, Zooplankton and Zoobenthos – Are There Specific Optima?



Two groups of polyunsaturated fatty acids (PUFA), termed omega-3 and omega-6 in food (or here as n-3 and n-6 PUFA, respectively), are essential for all vertebrates and probably also for nearly all invertebrates. The absolute concentrations of the different PUFA are important, as is an appropriate balance between the two. The optimal ratio of n-3/n-6 is not known for most organisms but is anticipated to be more or less species-specific (Sargent et al. 1995). The three most important PUFA in vertebrates are eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (ARA, 20:4n-6). Both EPA and ARA are precursors for biologically active eicosanoids that are vital components of cell membranes and play many dynamic roles in mediating and controlling a wide array of cellular activities (Crawford et al. 1989; Harrison 1990; Henderson et al. 1996; see Chap. 9). Since n-3 and n-6 PUFA cannot be synthesized de novo by most metazoans, they must be included in the diet, either as EPA, DHA and ARA, or as their precursors, such as α-linolenic acid (ALA, 18:3n-3, precursor of EPA and DHA) and linoleic acid (LIN, 18:2n-6, precursor of ARA) (Bell et al. 1986; Sargent et al. 1995). Both ALA and LIN are produced in the thylacoid membranes of algae and plants with chlorophyll (Sargent at al. 1987).


Arctic Charr Feeding Experiment PUFA Content Fatty Acid Ratio Scenedesmus Obliquus 



We thank J. Johansson for chemical analyses, I. Ahlgren for help with collecting references and comments on the early manuscript, and several colleagues, such as J. Persson, M.T. Brett, M. Kainz and C, Schlechtriem, M.T. Arts and O.E. Johannsson, for the use of their data. We also bothered D.C. Müller-Navarra and E. von Elert several times with questions about original data. Important remarks of an anonymous referee improved an earlier version of this work. We are also deeply thankful to the editors, M.T. Arts, M.T. Brett and M. Kainz, whose support and encouragement made this chapter possible.


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Authors and Affiliations

  1. 1.Department of Ecology and Evolution (Limnology)Uppsala UniversityUppsalaSweden
  2. 2.Department of Ecology and Environmental SciencesUmeå UniversityUmeåSweden
  3. 3.Department of Environmental AssessmentSwedish University of Agricultural SciencesUppsalaSweden

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