Diet-induced differences in the essential fatty acid (EFA) compositions of larval Atlantic cod (Gadus morhua L.) with reference to possible effects of dietary EFAs on larval performance

We studied the performance of cod rearing in which live feed was given under three different essential fatty acid (EFA) enrichment regimes, using commercially available live-feed enrichments, We assessed the fatty acid profile [docosahexaenoic (DHA), eicosapentaerroic (EPA), and arachidonic acid (AA)] in larval somatic tissue, relative to its amounts in both rotifers and Artemia as well as to larval performance. Overall, percentage lipid level of each experimental diet for the trial was approximately 50%. Further, there were no significant differences in total fatty acid levels of larvae from each treatment at the end of the trial (mean = 444.76 mu g fatty acid per mg lipid). However, during the rotifer phase, larvae from each treatment were able to incorporate comparable levels of %DHA, irrespective of levels in the diet. Despite this, the rotifer diet with more %DHA still promoted better larval growth than other treatments. Conversely, larvae from two of the treatments did not exhibit any accumulation of AA, reflecting levels found in the diet instead. However, between-tank differences in larval %AA showed improved growth during the rotifer period when larval %AA was high. Low ratios of EPA had no effect. During the Artemia phase, percentage levels of larval DHA decreased; there was no accumulation of DHA relative to dietary levels, which in Artemia were significantly lower than in rotifers (6 cf. 20-30%). However, DHA levels in larvae at the end of the experiment correlated positively with survival. Artemia contained lower levels of AA than rotifers (1.5 cf. 3.0%), yet comparable levels of AA were found in rotifer-fied and Artemia-fed larvae. This also differed significantly between treatments, and correlated positively with survival. (c) 2005 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.