Influence of lipid class and fatty acid deficiency on survival, growth, and fatty acid composition in rainbow trout juveniles

Triplicate groups of rainbow trout (182 ± 51 mg) were fed four experimental casein-gelatin based diets containing different fatty acid levels for 8 weeks. Diet 1, containing only the oleic acid methyl ester (18:1n - 9), was used as an essential fatty acids deficient diet. Diet 2, supplemented with olive and linseed oils was designed to provide moderate amount of linoleic (18:2n - 6) and linolenic (18:3n - 3) acids in the form of triglycerides. Diet 3 contained cod liver oil and provided highly unsaturated fatty acids (HUFA) as well as their precursors. Diet 4, supplemented with soy-refined lecithin, contained high levels of 18:2n - 6 in the form of phospholipids. At the end of the experiment, the growth of fish fed the lecithin supplemented diet was significantly higher (17 fold increase) than that of the other groups (6-14 fold increase). Survival was significantly lower in fish fed the diet 1 in comparison to fish fed the other experimental diets (57.8% vs. 84.4-86.7%). Fish fed diets 1 and 4 contained significantly less total and neutral lipids in the whole body than fish fed diets 2 and 3. Whole body fatty acid profiles from both neutral and phospholipid fractions closely reflected dietary fatty acid composition. Fish fed linoleate containing phospholipids preferentially deposited this fatty acid in neutral lipids (33.0 ± 1.6%) in comparison to body phospholipids deposition (21.2 ± 1.0%). An increase of dietary linoleate also resulted in a significantly higher percentage of arachidonate (20:4n - 6) in fish body phospholipids. In conclusion, selective accumulation of 18, 20, and 22 polyunsaturated fatty acids in body of juvenile rainbow trout is the function of fatty acid origin, e.g., lipid class, which has been very little studied in this species.