Effect of combination feeding of Nannochloropsis and freshwater Chlorella on the fatty acid composition of rotifer Brachionus plicatilis in a continuous culture

A continuous culture of rotifer was conducted to investigate the effect of combination feeding of both a high density of Nannochloropsis oculata (N) and condensed freshwater Chlorella (FC) on the fatty acid composition of L-type rotifer Brachionus plicatilis in a continuous culture system. The algal feeding of the rotifers was carried out in three successive steps: N-feeding -> N+FC-feeding -> FC-feeding. The culture was conducted at 24 degrees C and 25-27 psu in a 2000 mL bottle with 50% of water exchanged daily. The combination N+FC-feeding was effective in increasing rotifer density. The rotifers fed on N+FC (N+FC-R) had more non-polar lipids than polar ones, similar to those on N (N-R), opposite to the rotifers fed on FC (FC-R). N+FC-R contained higher levels of 16:2, 18:2n-6 (linoleic acid [LA]) and 20:2n-6, but lower levels of 18:1, 20:4n-6 (arachidonic acid), 20:5n-3 (eicosapentaenoic acid [EPA]) and 22:5n-3 (docosapentaenoic acid [DPA]) compared with N-R. Whereas N+FC-R contained higher levels of 16:1n-7, EPA and DPA, but lower levels of 16:2 and LA compared with FC-R. N+FC-R had more DPA in polar lipids than in non-polar ones. The Sigma n-6/Sigma n-3 ratio in N+FC-R was 0.9-1.0, significantly different from those in N-R (0.4) and FC-R (6.6-8.4). Therefore, it is inferred that the fatty acid profile of the N+FC-R cultured in a continuous culture system was affected by both N and FC. Also, the combination N+FC-feeding may be effective in manipulating the Sigma n-6/Sigma n-3 ratio in continuously cultured rotifers.