The presence of valuable bioactive compounds in European eel (Anguilla anguilla) skin was studied. For it, proximate and lipid class compositions and analysis of the fatty acid (FA) profile (individual FAs; FA groups, i.e., saturated, monounsaturated, and polyunsaturated; FA ratios, i.e., polyunsaturated/saturated, ω3/ω6) were determined and compared to the composition of the eel muscle. As a result, higher (p<0.05) levels of proteins (271.6 g·kg-1), lipids (38.0 g·kg-1), ash (27.7 g·kg-1) and ω6 FAs were observed in the skin tissue. Contrary, the muscle tissue showed higher (p<0.05) moisture, ω3 FA and ω3/ω6 values. Regarding lipid classes, a higher (p<0.05) proportion of phospholipids (111.1 g·kg-1 lipids), sterols (104.7 g·kg-1 lipids), α-tocopherol (274.0 mg·kg-1 lipids), and free fatty acids (43.6 g·kg-1 lipids) was observed in the skin tissue. No differences (p>0.05) between both tissues could be detected for triacylglycerol and FA group (saturated, monounsaturated, and polyunsaturated) values, as well as for the polyunsaturated/saturated ratio. It is concluded that eel skin, a by-product resulting from commercial processing, can be considered a valuable source to provide the food and pharmaceutical industries with useful value-added constituents such as proteins, lipids, ω3 FAs, phospholipids, and α-tocopherol.

Fatty acid desaturase 2 (Fads2) is the key enzyme of long chain polyunsaturated fatty acid (LC-PUFA) biosynthesis. Endogenous production of these biomolecules in vertebrates, if present, is insufficient to meet demand. Hence, LC-PUFA are considered as conditionally-essential. At present however, LC-PUFA are globally-limited nutrients due to anthropogenic factors. Attention of research is given therefore to find ways to maximize endogenous LC-PUFA production especially in production species, whereby deeper knowledge on molecular mechanisms of enzymatic steps involved is being generated. This review first briefly informs about the milestones in the history of LC-PUFA essentiality exploration before it focuses on the main aim – to highlight the fascinating Fads2 potential to play roles fundamental to adaptation to novel environmental conditions. Investigations are summarized, which elucidate the evolutionary history of fish Fads2 providing an explanation for the remarkable plasticity of this enzyme in fish. Further, structural implications of Fads2 substrate specificity are discussed and some relevant studies performed on organisms other than fish are mentioned in cases when such studies have so far not been conducted on fish models. The importance of Fads2 in the context of growing aquaculture demand and dwindling LC-PUFA supply is depicted and a few remedies in the form of genetic engineering to improve endogenous production of these biomolecules are outlined.