Neutral and polar lipid fatty acids in five families of demersal and pelagic fish from the deep Northwest Atlantic

Fatty acids in neutral and polar lipids were used to investigate trophic connections in species from five families of demersal (Rajella fyllae, Malacoraja senta, Alepocephalus bairdii, Borostomias antarcticus) and pelagic fish (Bathytroctes macrolepis, Lampanyctus spp., Chaulidos sloani, Serrivomer beanii) sampled in the deep Atlantic Ocean off Newfoundland, Canada. Lipid extracts were fractionated into neutral, acetone-mobile polar, and phospholipids to separate fatty acids in storage from those in membranes. Multivariate analysis of fatty acids showed that there were greater differences among the three lipid fractions than there were among the species when all fatty acid fractions were considered together. Neutral lipid fatty acids were characterized by monoenes, acetone-mobile polar lipids (AMPL) by C-18 polyenes, and phospholipids by 16:0 and DHA. Multivariate analysis of fatty acids in phospholipids showed a strong grouping by taxonomic family (>80% similarity), while the neutral lipid fatty acids showed a weaker grouping by family (72.5% similarity) but groupings that also related to habitat and vertical migration. The neutral lipid data supported the use of 20:1 omega 9 as a biomarker of calanoid copepods and of 16:1 omega 7 as a marker of diatoms to determine food web connections in deep-sea fish, but not some other common markers. In addition, correlations with delta N-15 showed that series of omega 6 and omega 7 fatty acids were trophically transferred though neutral lipids, especially the essential fatty acid, ARA. Neutral lipids were also reservoirs for essential omega 3 fatty acids in demersal species, but the major reservoir for DHA was AMPL and phospholipid in pelagic species.