Is ω6 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 ω6DPA (8.6% α 0.6%), which was reflected in the rotifers fed this protist (8.7% α 0.2%). This fatty acid was also unusually 13C‐enriched in both the protists (211.63% α 0.11%) and the rotifers (‐11.83% α 0.39%). The proportions of ω6DPA were very low in prefeeding cod larvae but they increased 30‐fold by d 11; however, ω6DPA showed the smallest δ13C 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 ω6DPA being essential at least in the early life stages of these two very different groups.