EFFECTS OF DIETS RICH IN LINOLEIC (18/2N-6) AND ALPHA-LINOLENIC (18/3N-3) ACIDS ON THE GROWTH, LIPID CLASS AND FATTY-ACID COMPOSITIONS AND EICOSANOID PRODUCTION IN JUVENILE TURBOT (SCOPHTHALMUS-MAXIMUS L)

Three practical-type diets utilizing fishmeal and casein as the protein sources and containing fish oil (FO), safflower oil (SO) or linseed oil (LO) were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 1.2 g for a period of 12 weeks. No differences in final weight, mortality or development of pathological lesions were evident either between duplicate tanks or between dietary treatments over this period. Fish fed diets containing SO and LO contained significantly greater amounts of liver triacylglycerol compared to fish fed FO. The major C18 polyunsaturated fatty acids (PUFA) in SO and LO diets, 18:2(n - 6) and 18:3(n - 3) respectively, were readily incorporated into both total lipid and individual phospholipids of turbot tissues. There was no accumulation of the DELTA6-desaturation products of these fatty acids, namely 18:3(n - 6) and 18:4(n - 3), in any of the tissues examined. The products of elongation of 18:2(n-6) and 18:3(n - 3), 20:2(n - 6) and 20:3(n - 3) respectively, accumulated in both total lipid and phospholipids with the highest levels of 20:2(n - 6) in liver PC and 20:3(n - 3) in liver PE. Eicosapentaenoic acid [EPA, 20:5(n - 3)] levels exceeded those of arachidonic acid [AA, 20:4(n - 6)] in phosphatidylinositol (PI) from liver and gill of fish fed LO. EPA levels in liver PI from fish fed LO were 3-fold and 2-fold greater than SO-fed and FO-fed fish, respectively. Fish fed diets containing SO and LO had significantly reduced levels of AA in liver and muscle total lipid and lower AA in individual phospholipid classes of liver and gill compared to FO-fed fish. The concentration of thromboxane B2 was significantly reduced in plasma and isolated gill cells stimulated with calcium ionophore A23187 of fish fed SO and LO compared to those fed FO. Prostaglandin E produced by isolated gill cells stimulated with A23187 was significantly reduced in fish fed both SO and LO compared to fish fed FO.