Fatty acid content and composition in tissues of Baikal grayling (Thymallus baicalensis), with a special focus on DHA synthesis

Long-chain polyunsaturated fatty acids of n-3 family (n-3 LC PUFAs) are physiologically essential compounds required for normal growth and development of animals, including humans. The ability of fish species to synthesize n-3 LC PUFAs varies significantly across different trophic levels. We have studied fatty acid (FA) content (mg/g of wet weight) and level (% of total FAs) in the brain, liver, heart, intestine, female and male gonads, muscle, and adipose tissues of commercially important wild freshwater Baikal grayling. Additionally, FA content and level of Baikal grayling juveniles have been studied. In all tissues of Baikal grayling, some LC PUFAs, namely, 24:5n-3 and 24:6n-3 (C24 PUFAs), have been found. These FAs are the intermediate products in the synthesis of docosahexaenoic acid (DHA, 22:6n-3) by the Sprecher pathway. The levels of C24 PUFAs in tissues differed significantly: the highest levels of C24 PUFAs were found in adipose tissue and the lowest values in the gonads of females, liver, brain, and head of juveniles. According to the dynamics of DHA and C24 PUFAs, the maximum rate of DHA synthesis is achieved in brain of Baikal grayling, while the lowest rate of DHA synthesis probably occurs in adipose tissue. Although all studied tissues had differences in the number of FAs and their levels, 16:0, 18:1n-9, 16:1n-7, 20:5n-3, and DHA dominated. Male gonads contained an extremely high level of furan FAs — presumably beneficial substances for human health. Additionally, the nutritional value of the tissues of Baikal grayling as a source of n-3 LC PUFAs for humans has been estimated.