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Effect of enrichment time and dietary DHA and non-highly unsaturated fatty acid composition on the efficiency of DHA enrichment in phospholipid of rotifer (Brachionus Cayman)

Li, Keshuai, Olsen, Yngvar
Aquaculture 2015 v.446 pp. 310-317
Brachionus, diet, fatty acid composition, fiberglass, fish larvae, live feeds, marine fish, phosphatidylcholines, phosphatidylethanolamines, starvation, unsaturated fatty acids
An increasing number of studies suggest that DHA associated with dietary phospholipid (PL) is better metabolically available for fish larvae. Knowledge on how to increase DHA levels in the major PL classes of the live feed is needed. Brachionus Cayman was cultured in conical fibreglass vessels, enriched with commonly used commercial diet Multigain or DHA Selco (DSelco) in flat bottom vessels at 20°C. The changes of DHA content in the PL of the rotifers through enrichment and through a starvation phase post-enrichment were investigated in order to define an appropriate enrichment time and to test the stability of DHA post-enrichment. The different dietary non-HUFA (non-highly unsaturated fatty acid) composition of DSelco (25.1% SFA, 32.1% MUFA) and Multigain (40.7% SFA, 2.11% MUFA) allowed an evaluation on how SFA and MUFA might affect the efficiency of DHA enrichment of phospholipid in the rotifers. Rotifer samples were collected at 0h, 1h, 2h, 4h, 8h, 12h and 24h after initiation of enrichment. Total lipid (TL) and the fatty acid composition in TL, phosphatidylcholine (PC) and phosphatidylethanolamine (PE) of rotifers and enrichment diets were analysed. The highest DHA levels in PC (23.0%) and PE (16.5%) in Cayman were found after 24h enrichment with Multigain, and levels were far higher than obtained earlier. The enriched DHA was stable at 10°C for at least 24h post-enrichment under starving conditions (p>0.05), whereas a significant (p<0.05) decrease of DHA was observed during starvation at 20°C. In order to obtain high DHA levels in PC and PE in rotifers, the enrichment time is suggested to be at least 24h to maximise the efficiency of DHA enrichment in PL and the enrichment diet should have a high DHA content. The feeding rations should be low to reduce the total lipid contents of the rotifers. The overall results allowed us to propose a hypothesis that 18:1n9 can inhibit DHA incorporation through competition whereas 16:0 can facilitate DHA incorporation into PL. The hypothesis needs to be further tested.The paper is bringing information about fatty acid enrichment of rotifers in questions that are so far quite unclear and could have a strong impact on larviculture of marine fish larvae. This study shows methods to obtain high level of DHA in phospholipids of rotifer. The results could potentially have a significant impact to improve current fatty acid enrichment protocols for rotifers.