We examined trophic positions and fatty acid concentrations of riverine, lacustrine, and aquaculture diet and fish in Austrian pre-alpine aquatic ecosystems. It was hypothesized that dietary fatty acid (FA) profiles largely influence the FA composition of the salmonids Salvelinus alpinus, Salmo trutta, and Oncorhynchus mykiss. We analyzed trophic positions using stable isotopes (d 15 N) and tested for correlations with polyunsaturated fatty acid (PUFA) concentrations. Gut content analysis revealed benthos (rivers), pellets (aquaculture), and zooplankton (lakes) as the predominant diet source. Results of dorsal muscle tissues analysis showed that the omega-3 PUFA, docosahexaenoic acid (DHA; 22:6n -3), was the mostly retained PUFA in all fish of all ecosystems, yet with the highest concentrations in S. alpinus from aquaculture (mean: 20 mg DHA/g dry weight). Moreover, we found that eicosapentaenoic acid (EPA; 20:5n -3) in fish of natural habitats (rivers, lakes) was the second most abundant PUFA (3-5 mg/g DW), whereas aquaculture-raised fish had higher concentrations of the omega-6 linoleic acid (18:2n -6; 9-11 mg/g DW) than EPA. In addition, PUFA patterns showed that higher omega-3/-6 ratios in aquacultures than in both riverine and lacustrine fish. Data of this pilot field study suggest that salmonids did not seem to directly adjust their PUFA to dietary PUFA profiles in either natural habitats or aquaculture and that some alterations of PUFA are plausible. Finally, we suggest that trophic positions of these freshwater salmonids do not predict PUFA concentrations in their dorsal muscle tissues.

This study investigated effects of linseed or fish oilenriched finishing diets on the polyunsaturated fatty acids (PUFA) composition in dorsal muscle tissues of pond-cultured common carp (Cyprinus carpio). After 180 days of dietary exposure to cereal diet containing vegetable oil (1%), carp were exposed to 7% linseed (LO) or 7% fish oil-enriched (FO) finishing diets for 30 days. FO supplied 17 and 20 mg fish À1 day À1, respectively, of the long-chain n-3 fatty acids eicosapentaenoic and docosahexaenoic acid for 30 days and doubled long-chain PUFA concentrations in carp of the FO pond. The increased supply of short-chain PUFA in LO resulted in higher short chain, but not long-chain PUFA, showing that there was very little PUFA conversion. Thus, dietary short-chain PUFA could not compensate for the low levels of dietary long-chain PUFA in LO. However, moderate supply of dietary long-chain PUFA in finishing diets for 30 days is very efficient in increasing nutritionally important long-chain PUFA concentrations in carp.