Examining the transport of dietary lipids to egg and muscle tissue in cultured coho salmon Oncorhynchus kisutch during secondary oocyte growth

This research examined the transport of dietary lipids to developing eggs in coho salmon Oncorhynchus kisutch during secondary oocyte growth and evaluated the potential of a pre-harvest finishing feed to significantly increase the concentration of docosahexaenoic acid, DHA, in egg and muscle lipids at harvest. Four groups of fish were fed one of two experimental feeds during different intervals of secondary oocyte development. The feeds contained lipids with different fatty acid compositions and markedly different stable 13C isotope signatures. Fish from two of the treatments were subsequently spawned in captivity to assess the potential impact of increased DHA levels on egg and fry quality. Egg and muscle lipid fatty acid concentrations were significantly affected by treatment ( P<0.001) during all three stages of oocyte development. Stable 13C isotope analyses confirmed that dietary lipids were incorporated into both egg and muscle lipids (P<0.001) and revealed that egg lipids were more effected than muscle lipids during vitellogenesis. Arachidonic acid, ARA was preferentially incorporated into egg lipids over muscle lipids at the highest rate of all fatty acid examined with the greatest uptake observed during pre-vitellogenic stages (P=0.015). Increased levels of dietary linoleic acid, LA, was associated an increased bioconversion of LA to ARA by the fish during vitellogenesis. Docosahexaenoic acid, DHA, was preferentially incorporated into egg lipids over muscle lipids with the greatest uptake observed during the lipid droplet stage of development (P=0.033). The presence of an ovary specific fatty acid binding protein is proposed. Within a treatment, the delta13C values of all plasma lipoprotein classes were similar during vitellogenesis indicating that all lipoprotein lipids originated from a common pool of exogenous and endogenous lipids. Embryo and fry survival and fry growth were similar between the two treatment groups in the spawning study. Results from this research demonstrate the potential of finishing feeds to greatly influence the fatty acid profiles of both muscle and egg lipids in maturing coho salmon. Use of the proposed finishing feed during vitellogenesis resulted in the production of high DHA eggs for the roe market without a reduction the quality of eggs for spawning.