Content of polyunsaturated fatty acids essential for fish nutrition in zoobenthos species

Content of eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) and the n-3/n-6 ratio are important indicators of nutritive value of aquatic invertebrates as food for fish. We studied fatty acid (FA) content and composition of 68 zoobenthic species. Benthic invertebrates differed significantly in their contents of EPA and DHA and n-3/n-6 ratios. The most valuable food for fish were Insecta, especially Ephemeroptera and Trichoptera, Gammaridae, and Turbellaria (Dendrocaelopsis sp.). The invertebrates of low food quality for fish were Hirudinea, Mollusca, Oligochaeta, Bryozoa (Plumatella emarginata), and Coleoptera (Dytiscus lapponicus). Our data suggest that the recent and ongoing global replacement of native species, mainly Insecta, by invaders, mostly represented by Mollusca, Crustacea, Polychaeta, Oligochaeta, Bryozoa, and Hirudinea, probably will reduce the nutritive value of food sources for benthivorous fish. In addition, some of the taxa studied have peculiar FAs, which may be useful as their markers in trophic webs. Thus, 20:1n-13, 20:2n-6, 22:5n-3, and 22:6n-3 are likely to be considered markers of Mollusca, Hirudinea, Turbellaria, and Gammaridae, respectively, for tracing food webs in freshwater ecosystems.