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

Abstract

Female 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.

Received October 26, 2010; accepted February 21, 2011

ACKNOWLEDGMENTS

We are grateful to Kerry Huber (University of Idaho), Ronald Hardy (University of Idaho), and Barbara Rasco (Washington State University) for their critical reviews and helpful comments on the manuscript. We also thank David Deavila (Center for Reproductive Biology, Washington State University) for performing the plasma vitellogenin analysis. Lastly, we are grateful to Jason Frost (U.S. Department of Agriculture) for top-dressing the feeds for the study at the Bozeman Fish Technology Center (U.S. Fish and Wildlife Service, Bozeman, Montana).

Notes

^aNL fraction consisted of monoacylglycerols, diacylglycerols, triacylglycerols, cholesterol, cholesterol esters, and free fatty acids.

^bPL fraction consisted of phospholipids.

^cThe SGR was calculated for the period 1 September 2008 to 6 January 2009 (both treatments).

^dFish oil feed contained whole fish meal, wheat flour, stabilized sardine oil, poultry by-product meal, krill meal, corn gluten, soybean meal, astaxanthin, vitamin premix, and mineral premix. Cost in 2008 was US$0.44 per kilogram.

^eAlgal oil feed contained whole fish meal, wheat flour, stabilized algal oil–corn oil blend, poultry by-product meal, krill meal, corn gluten, soybean meal, astaxanthin, vitamin premix, and mineral premix. Cost in 2008 was $3.50 per kilogram.

^aSum of saturated fatty acids (SFAs): 14:0, 16:0, 18:0, 20:0, 22:0, and 24:0.

^bSum of n-9, n-7, and n-11 isomers.

^cSum of monounsaturated fatty acids (MUFAs): 14:1, 16:1, 18:1, 20:1, 22:1, and 24:1.

^dSum of n-6 fatty acids: 18:2, 20:2, 20:3, and 20:4.

^eSum of n-3 fatty acids: 18:3, 18:4, 20:3, 20:4, 20:5, 21:5, 22:5, and 22:6.