Preliminary evaluation of canola oil, pork lard and marine lipid singly and in combination as supplemental dietary lipid sources for juvenile fall chinook salmon ( Oncorhynchus tshawytscha)

Abstract

Canola oil, pork lard and herring oil singly and in various combinations were assessed as supplemental sources of dietary lipid for juvenile fall chinook salmon held in running, aerated 10–12°C well water on a natural photoperiod for 62 days. Each of the six different types of supplemental lipid comprised about half of the total lipid content (16% of dry matter) in an experimental dry diet (West Van 32). Some groups received Oregon Moist Pellets (OMP), a practical hatchery diet. Thereafter, the performance of the groups was evaluated in running, aerated 10–14°C seawater for 35 days when all fish received OMP. The type of supplemental dietary lipid did not significantly influence fish growth in freshwater. All groups fed the test dry diets had significantly higher food and protein conversion than those receiving OMP. Best overall food and protein utilization occurred in fish fed West Van 32 supplemented with canola oil or an equal mixture of herring oil with canola oil or lard. Mortality was negligible in all groups. Body lipid composition generally mirrored that of dietary lipids except (1) percentages of docosahexaenoic acid (C22:6ω3) were higher in body lipids than in dietary lipids, (2) groups receiving supplemental canola oil (C), lard (L) or a combination of these sources (C-L) had elevated percentages of ω3 fatty acids in their body lipids and, (3) the range for percentages of saturated fatty acids in body lipids (15.7–22.8%) was smaller than that noted for dietary lipids (12.5–29.5%). None of the groups showed any ability to metabolically convert dietary linoleic acid (C18:2ω6) to arachidonic acid (C20:4ω6). However, contrary to other studies on rainbow trout and coho salmon, the fall chinook salmon in this study metabolically adapted to a high dietary level of ω6 fatty acids (2.6% or 16.2% of dietary lipid level) when the diet simultaneously contained 2.7% ω3 fatty acids. Nutritional history in freshwater did not compromise performance in seawater when all groups received OMP. Also, the body lipid compositions of the test groups were transformed to reflect that of OMP after 35 days of seawater culture. It is concluded that canola oil, pork lard and a blend of these lipid sources are potentially excellent alternative types of supplemental dietary lipid for juvenile fall chinook salmon destined for ocean release.