EFFECTS OF DIFFERENT DIETARY ARACHIDONIC-ACID - DOCOSAHEXAENOIC ACID RATIOS ON PHOSPHOLIPID FATTY-ACID COMPOSITIONS AND PROSTAGLANDIN PRODUCTION IN JUVENILE TURBOT (SCOPHTHALMUS-MAXIMUS)

Five purified diets containing AA (20:4n-6) at 0.02-0.78% dry weight a nd DHA (22:6n-3) at 0.93-0.17% dry weight were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 0.87 g fo r a period of If weeks. The dietary DHA:AA ratio ranged from 62 to 0.2 . Incorporation of AA into liver phospholipids increased with increasi ng dietary AA input. Phospholipids from fish fed diets containing 0.02 , 0.06 and 0.11% of dry weight as AA generally contained less AA compa red to fish fed fish oil while those fed diets containing 0.35 and 0.7 8% of dry weight as AA had higher AA levels in their phospholipids. Th e highest levels of AA were found in PI but the greatest percentage in crease in AA incorporation was in PE and PC. Brain phospholipid fatty acid compositions were less altered by dietary treatment than those of liver but DHA content of PC and PE in brain was substantially lower i n fish fed 0.93% pure DHA compared to those fed fish oil. This suggest s that dietary DHA must exceed 1% of dry weight to satisfy the require ments of the developing neural system in juvenile turbot. In both tiss ues, (20:5n-3) concentration was inversely related to both dietary and tissue PI AA concentration. Similar dietary induced changes in AA, EP A and DHA concentrations occurred in the phospholipids of heart, gill and kidney. PGE(2) and 6-ketoPGF(1 alpha), were measured in homogenate s of heart, brain, gill and kidney. In general, fish fed the lowest di etary AA levels had reduced levels of prostaglandins in their tissue h omogenates while those fed the highest level of AA had increased prost aglandin levels, compared to fish fed fish oil. In brains, the PGE(2) concentration was only significantly increased in fish fed the highest dietary AA.