Transitioning Coho Salmon Broodstock to a Docosahexaenoic Acid (DHA)‐Rich Diet during Vitellogenesis: Effects on Egg Composition and Embryo and Fry Quality

Abstract

AbstractFemale coho salmon Oncorhynchus kisutch were fed one of two broodstock diets during vitellogenesis to evaluate the contribution of dietary lipids to egg lipids and to assess any embryo or fry quality differences that were attributable to treatment. The diets contained lipids with different fatty acid profiles and carbon stable isotope signatures (δ13C). Diets were formulated by top‐dressing a low‐fat salmon broodstock feed with either sardine oil (fish oil feed) or an algal oil–corn oil blend (algal oil feed). The added oils were balanced for total n‐3 fatty acid content but contained markedly different levels of linoleic acid (LA), eicosapentaenoic acid, and docosahexaenoic acid (DHA). Analysis of δ13C revealed that dietary lipids were significantly incorporated into egg lipids during vitellogenesis and that polar and neutral lipid fractions were equally affected. Eggs of fish in the algal oil treatment group had significantly higher levels of DHA and significantly lower protein content than the eggs of fish in the fish oil treatment group. Embryo survival and fry survival and growth were similar between the two treatment groups. Eggs from the algal oil treatment additionally had higher levels of LA, and there was evidence of direct elongation of LA to eicosadienoic acid (20:2[n‐6]) and bioconversion of LA to arachidonic acid by the fish. Results from this experiment demonstrate the feasibility of increasing the DHA content of egg lipids in cultured salmonids without a concomitant decrease in egg or fry quality. The proposed enrichment would allow for the production of a value‐added, high‐DHA product for the cured roe market without reducing the value of eggs that are destined for the hatchery market.