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We studied amino acid ( AA) composition of epilithic biofilms and zoobenthos near the shore at a middle section of the Yenisei River ( Siberia, Russia). We hypothesised that there was an imbalance between the composition and content of amino acids in the biofilm and its consumers, the zoobenthos, as well as between those in the zoobenthos and fish., Based on monthly sampling from 2007 to 2010, there was seasonal variation in AA profiles in the epilithic biofilms, probably caused by the succession of microalgal and cyanobacterial species., Overall, there was an imbalance in the percentage of the essential amino acids (lysine and histidine) between benthic animals and their food (the epilithic biofilm), which suggests that benthic animals may be limited by food quality. Moreover, the zoobenthos had a significantly higher content of AA, relative to carbon, than the biofilm., Based on sampling in 2012, there was an imbalance between the AA profiles of zoobenthos and that of their main consumer, the Siberian grayling ( Thymallus arcticus), particularly in the percentages of two essential amino acids, lysine and leucine., In terms of overall content of essential amino acids, the nutritional value to fish of gammarids, which have recently invaded the river, was significantly lower than that of indigenous taxa, trichopteran and chironomid larvae. [ABSTRACT FROM AUTHOR]