Fatty acid and lipid class composition in cutaneous mucus of Atlantic salmon, Salmo salar (L.)

Abstract

The surface mucus of fish is a physical and biochemical barrier that plays roles in osmoregulation, chemical communication and protection against physical damage (e.g. by abrasion and ultraviolet radiation), chemical insults (e.g. toxins, heavy metals and irritants) and biological threats (e.g. posed by predators, parasites and pathogens) (Alvarez-Pellitero, 2008; Dash et al., 2018; Ellis, 2001; Esteban, 2012; Kumari et al., 2019; Reverter et al., 2018; Shephard, 1994). The major structural constituents of fish cutaneous mucus are mucins (highly glycosylated high molecular weight proteins), in addition to other proteins, carbohydrates, lipids, nucleic acids and ions like calcium (Brinchmann, 2016; Shephard, 1994). Cutaneous mucus composition has been determined to differing extents for various fish, from gilthead sea bream Sparus aurata (L.) (Pérez-Sánchez et al., 2017) to stingray Hypanus americanus (Hildebrand & Schroeder, 1928) (Coelho et al., 2019). However, most studies focused on proteinaceous or immune-relevant constituents, whilst few studies have characterized the lipid and fatty acid constituents despite influencing mucus properties (Jais et al., 1998; Lewis, 1970; Rahman et al., 2012; Sato et al., 2008; Torrecillas et al., 2019). Earlier studies determined fatty acids for total lipids only, whilst only Torrecillas et al. (2019) analysed the fatty acids in neutral and polar lipid fractions separately, meaning there are no reports detailing the fatty acids within distinct lipid classes of fish skin mucus. Therefore, the aim of this present study was to characterize the fatty acids and lipid classes of the skin mucus of the key farmed species, Atlantic salmon Salmo salar (L.).