We studied biogeochemical characteristics, including organic carbon and nitrogen contents, fatty acid (FA) composition, stable isotope ratios, and primary production in conjunction with species composition of bacterioplankton, using next generation sequencing, in the Yenisei River along a distance ∼1800 km. Basing on FA composition of particulate organic matter (POM) and on other indicators of sources of POM, the river was subdivided into four sections. The upper section 1, situated in mountain region, was the net source of high‐quality autochthonous organic matter, produced primarily by diatoms and partly consumed by specialized bacteria species. Section 2 in plain taiga was net sink of high quality allochthonous and autochthonous organic matter, produced by cyanobacteria and green algae. Section 3 was net sink of organic matter, primarily allochthonous, consumed by the specialized species of bacteria. The lowest section 4, situated in tundra, was primarily the conduit of recalcitrant terrestrial organic matter, but also the net source of autochthonous organic matter, produced by diatoms. Biogeochemical traits of sections of the Yenisei River evidently shaped dominant species composition of bacterioplankton of these sections. Regarding the biogeochemical and microbiological data, we concluded that the Yenisei River ecosystem complexly combines features of river mosaic, river continuum, and “neutral pipe.”
In several Russian northern lakes and rivers, Arctic cisco Coregonus autumnalis, least cisco C. sardinella, peled C. peled, tugun C. tugun, broad whitefish C. nasus, whitefish C. lavaretus and vendace C. albula were sampled in periods of officially permitted commercial fishery. Special attention was paid to contents (mg g of wet weight) of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in muscle tissues (filets), which are essential for human nutrition. The highest values of EPA + DHA content in semi-anadromous fish and freshwater fish were recorded for C. autumnalis from the Yenisei River, 17.60 mg g wet weight, and for C. lavaretus from the Sobachye Lake, 16.61 mg g wet weight, respectively. Intra-genus variations of EPA + DHA contents of Coregonus species were from 1.87 to 17.60 mg g wet weight. Since the congeneric species were genetically close to each other, the variations in EPA and DHA contents were thought to be caused primarily by ecological factors: migrational capability, type of feeding and trophic status of aquatic ecosystems. In general, the majority of studied species appeared to be of a high nutritive value for humans, although unfavorable environmental conditions could considerably diminish this value.
Long-chain omega-3 polyunsaturated fatty acids (LC-PUFA) essential for human nutrition are mostly obtained from wild-caught fish. To sustain the LC-PUFA supply from natural populations, one needs to know how environmental and intrinsic factors affect fish fatty acid (FA) profiles and contents. We studied seven Salmoniformes species from two arctic lakes. We aimed to estimate differences in the FA composition of total lipids and two major lipid classes, polar lipids (PL) and triacylglycerols (TAG), among the species and to evaluate LC-PUFA contents corresponding to PL and TAG in muscles. Fatty acid profiles of PL and TAG in all species were characterized by the prevalence of omega-3 LC-PUFA and C16-C18 monoenoic FA, respectively. Fish with similar feeding spectra were identified similarly in multivariate analyses of total lipids, TAG and PL, due to differences in levels of mostly the same FA. Thus, the suitability of both TAG and total lipids for the identification of the feeding spectra of fish was confirmed. All species had similar content of LC-PUFA esterified as PL, 1.9-3.5 mg g −1 , while the content of the TAG form strongly varied, from 0.9 to 9.8 mg g −1 . The LC-PUFA-rich fish species accumulated these valuable compounds predominately in the TAG form.
⎯Two fish species reared in aquaculture (pink salmon Oncorhynchus gorbuscha and whitefish Coregonus lavaretus) and ten fish species from natural habitats (whitefish C. lavaretus, tugun Coregonus tugun, broad whitefish Coregonus nasus, least cisco Coregonus sardinella, vendace Coregonus albula, boganid charr Salvelinus boganidae, charr Salvelinus alpinus complex, northern pike Esox lucius, sharp-snouted lenok Brachymystax lenok, and taimen Hucho taimen) have been studied. The content of two long-chain polyunsaturated omega-3 fatty acids (PUFAs), eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), in the muscle tissue of the fish and in their food (intestine contents) are compared. In the aquacultures of whitefish and pink salmon, the total content of EPA and DHA is significantly higher in feed than in the muscle tissue of the fish, which indicates losses of PUFA in the two-link food chain of the aquaculture during their transfer to the upper trophic level. EPA and DHA losses in aquaculture, which are confirmed by numerous literature data, mean an inefficient usage of the available sources of PUFAs and the aggravation of the global deficit of these biochemicals in the human diet. A study of natural fish populations reveals the accumulation of EPA and DHA in their biomass compared to food in many cases, although opposite phenomena are also observed. An assumption on the presence of an optimal, physiologically adequate species-specific level of PUFA in the fish muscle tissue has been made based on our data and literature data. If the level of PUFAs in the muscles is lower than optimal, their accumulation (bioaccumulation) from food and/or de novo synthesis are observed. When the optimal level is exceeded, the content of EPA and DHA in biomass approaches maximum species-specific values; however, part of these PUFAs entering from food is not digested or is catabolized. According to the obtained data, the species of the order Salmoniformes have an optimal level of 2 to 6 mg/g of wet weight. It has been found that in aquaculture approaching to maximum values of EPA + DHA content was accompanied by their losses (scattering) in the food chains, while in natural ecosystems the maximum values of PUFA content in the fish biomass are achieved by their accumulation from the lower trophic level. Boganid charr S. boganidae had the highest content of EPA + DHA in the muscle tissue among all known fish species (32.78 mg/g of wet weight).
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