Effect of season and trophic level on fatty acid composition andcontent of four commercial fish species from Krasnoyarsk Reservoir (Siberia, Russia)

tTwo groups of factors, phylogenetic and ecological, are presently regarded as controlling fatty acidcomposition of fish, including essential eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids. Envi-ronmental effects, e.g., trophic position, temperature and/or seasonality, were previously studied usingsums of fatty acids or only their level data. We tested the hypothesis that differences in trophic levels ofpiscivorous (pike and perch) and omnivorous (roach and bream) fish from a mesotrophic reservoir allowdiscriminating levels and contents of individual fatty acids, especially EPA and DHA. The more establishedmeasurements, i.e., stomach contents and carbon and nitrogen stable isotopes in fish muscles, were alsocarried out to provide linkages between the different ecological tracers, fatty acids versus stable isotopes,and matching the methods for long-term food sources (fatty acids and stable isotopes) and recent for-aging (stomach content analysis). We also studied a putative influence of seasonality. Similar to otherstudies, there were seasonal changes in fatty acid composition and contents of two fish, perch and roach,due to direct and indirect effects of water temperature. Meanwhile, the piscivorous and omnivorousspecies captured in the same month, were explicitly differentiated on a base of stable isotopes and fattyacids. Significantly higher percentages and contents of DHA in piscivorous fish, perch and pike, relativelyto those in roach and bream, likely indicated a higher trophic transfer efficiency for this essential fattyacid. All the fishes have commercial importance for regional fishery and are harvested from the studiedreservoir for human nutrition. Regarding content of EPA + DHA (mg g−1fish) as the indicator of nutritivevalue for humans, pike had the highest nutritive value, roach and perch had intermediate overlappedvalues, and bream was of the least benefit

Feeding spectra of Arctodiaptomus salinus (Calanoida, Copepoda) using fatty acid trophic markers in seston food in two salt lakes in South Siberia (Khakasia, Russia)

During two vegetation seasons (2004–2005), we compared feeding spectra of Arctodiaptomus salinus (Calanoida, Copepoda) populations inhabiting two neighboring salt lakes, Shira and Shunet, Khakasia, Russia, using fatty acid (FA) trophic markers. Sestonic FA composition in two lakes moderately differed, whereas levels of diatom FA markers were higher in Lake Shunet and of Cyanobacteria and green algae markers in Lake Shira. In general, markers in storage lipids—triacylglycerols (TAG) of A. salinus—reflected the differences in sestonic composition of the two lakes. Nevertheless, TAG fraction was also enriched by FA trophic markers of the minor components of seston, which were selectively ingested by the animals. In Lake Shira, A. salinus had significantly higher concentrations of bacterial FA markers in TAG. In Lake Shunet, TAG of A. salinus contained significantly higher relative amounts of 18:4ω3, 18:5ω3 and C22 polyunsaturated fatty acids (PUFA), which indicated marked contribution of cryptophytes or (and) flagellates into the diet. Laboratory experiments showed feeding on Cryptomonas and sulfur purple bacteria in Lake Shunet and ciliates and colonial picoplankton in both lakes, and generally confirmed the differences in FA trophic markers in A. salinus between the lakes. The two populations of A. salinus markedly differed in levels of essential long-chain PUFA, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, although the levels of these FA in seston were quite similar between the two lakes. The higher levels of the essential ω3 PUFA in A. salinus in Lake Shunet may be an adaptive response of the animals to a vertical stratification of physico-chemical conditions and significantly higher salinity levels at the boundary of adjacent bottom layer in this lake.