[Role of essential fatty acids in trophometabolic interactions in the freshwater ecosystems (a review)].

Polyunsaturated fatty acids (PUFA) of omega3 family are of crucial physiological importance for the most animals and they are an essential and deficient component of human nutrition. These compounds are most effectively synthesized by some groups of algae, hence, aquatic ecosystems are considered to be the main source of these PUFA for human nutrition. Factors controlling the content and distribution of omega3 PUFA in freshwater organisms of basic trophic levels and determined PUFA final production in freshwater ecosystems are considered in the review. PUFA biosynthesis is known to be tightly related to basic fatty acid metabolic pathways. Hence, fatty composition and the PUFA content of major freshwater hydrobiont groups, including bacteria, algae, invertebrates and vertebrates, and environmental and population age effects are described. The peculiarities of PUFA transfer between organisms of various trophic levels are discussed. The essential omega3 PUFA is one of the important parameter of food quality of aquatic consumers and they can determine the rate of energy and matter transfer between producers and primary consumers and, as a result, in a whole freshwater food chain. Analysis of PUFA content and its regulation in biomass of various fish populations indicates that freshwater ecosystems are of the same value in respect of PUFA sources as marine ecosystems. Despite the great practical importance, the studies focused on production and whole pools of omega3 PUFA in different freshwater ecosystems are still scarce and need to be continued.