Is omega 6 docosapentaenoic acid an essential fatty acid during early ontogeny in marine fauna?

A thraustochytrid marine protist (Schizochytrium sp.) was fed to rotifers (Branchionus plicatilis), which in turn, were fed to cod larvae (Gadus morhua). Samples of larvae 1 and 11 d after hatch, the rotifer diet, and the enrichment were collected for molecular and isotope analyses of fatty acids. Schizochytrium sp. had unusually high proportions of omega 6DPA (8.6% +/- 0.6%), which was reflected in the rotifers fed this protist (8.7% +/- 0.2%). This fatty acid was also unusually C-13-enriched in both the protists (-11.63 parts per thousand +/- 0.11 parts per thousand) and the rotifers (-11.83 parts per thousand +/- 0.39 parts per thousand). The proportions of omega 6DPA were very low in prefeeding cod larvae but they increased 30-fold by d 11; however, omega 6DPA showed the smallest delta C-13 change from the protist source. This, combined with reports of significantly higher growth rates in cod and scallops fed diets rich in this fatty acid, provide strong evidence for omega 6DPA being essential at least in the early life stages of these two very different groups.