Effects of weaning onto a pelleted diet on docosahexaenoic acid (22: 6 n-3) levels in brain of developing turbot (Scophthalmus maximus L)

Abstract

The brain lipid and fatty acid compositions of turbot, Scophthalmus maximus (L.), were determined in unweaned fish and in fish from the same batch that had been weaned 1 week earlier. Fish were maintained on the same dietary regime until the time of weaning. Immediately prior to weaning fish were fed enriched Artemia. At weaning, one group of fish was fed a dry pelleted food whereas the other group remained on enriched Artemia. The dry pelleted diet contained 2-fold more eicosapentaenoic acid (EPA, 20:5 n-3) and 13-fold more docosahexaenoic acid (DHA, 22:6 n-3) per mg dry weight than the Artemia. In weaned turbot, there were significant increases in brain dry weight (21.6% greater than in unweaned fish,P less than 0.05) and in the percentage of total polar classes in total lipid, due to a significant increase in the percentage of phosphatidylcholine (PC). There were no significant differences in the other lipid classes, with the exception of phosphatidylinositol (PI) which was significantly lower (P less than 0.05) in brain of weaned fish. The most striking effect of weaning on brain fatty acid composition was the rapid and specific incorporation of DHA into brain phosphoglycerides. The accumulation of DHA was highly significant in all phosphoglyceride classes, with the levels of DHA increased by factors of 52% in total lipid, 86% in PC, 62% in phosphatidylethanolamine (PE), 43% in phosphatidylserine (PS) and 31% in PI. The rapid incorporation of 22:6 n-3 in turbot brain lipids was discussed with respect to the roles of this fatty acid in neutral tissues during development. The implication for the aquaculture of this species is that brain DHA levels may be directly related to larval performance, with the low levels of DHA in the brains of unweaned fish an important factor in the high mortality of larvae experienced during the stage when live feeds are being offered.