Esterification and modification of [1-14C] n-3 and n-6 polyunsaturated fatty acids in pikeperch (Sander lucioperca) larvae reared under linoleic or α-linolenic acid-based diets and variable environmental salinities

Abstract

To elucidate the in vivo endogenous ability of pikeperch (Sander lucioperca) larvae to deacylate and reacylate phospholipids and to elongate and desaturate PUFAs, 20 days post hatch (DPH) fish were incubated with either [1-14C]20:4n-6 bound to PC and PE, or with free [1-14C]-labelled fatty acids (18:2n-6, 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3). The modulation capacity of both low LC-PUFAs but high 18C PUFAs precursors dietary supply and increasing salinity on larval fatty acid metabolic pathways was also investigated. [1-14C]DHA was incorporated into larval tissues to a lower extent than [1-14C]ARA or [1-14C] EPA. [1-14C]ARA was significantly less abundant in larval tissues when provided bound to PE than when esterified into PC, indicating that PC is a better phospholipid source to provide LC-PUFA to pikeperch larvae. Radioactivity was mainly recovered into phospholipids, especially that of the three LC-PUFAs ARA, EPA and DHA. All substrates were primarily incorporated into PC except [1-14C]ARA which significantly did into PI. Both [1-14C]EPA and [1-14C]DHA showed a similar esterification pattern into lipid classes: PC > PE > PI > TAG, with [1-14C]DHA presenting the highest esterification into PE of all radiolabelled compounds (26.3% vs 3.6–14.2%). Although higher rearing salinities tended to increase Δ6 desaturase activity, no radioactivity from [1-14C]18:2n-6 or [1-14C]18:3n-3 was detected in ARA or EPA, proving a deficiency of Δ5 activity and the inability of pikeperch to biosynthesize DHA. This work provides novel information on the lipid metabolism of pikeperch at early development necessary for the design of live prey enrichment protocols and dietary formulations adapted to larval metabolic capabilities.