Incorporation and turnover of essential fatty acids in phospholipids and neutral lipids of rainbow trout.

1. The turnover of rainbow trout (Salmo gairdneri) lipid was monitored in fish receiving essential fatty acids (EFA) replete and EFA deficient diets using [1-14C]-linolenic acid (C18:3 omega 3). 2. Forty percent of administered radioactivity was recovered in total lipid after 7 days. 3. Eighty-five percent of incorporated label was recovered in C18:3 omega 3 derivatives, primarily docosa-hexaenoic acid (22:6 omega 3). 4. Over 10 weeks, 14C activity in neutral lipid (NL) remained constant whereas that in phospholipid (PL) declined due to loss of label from shorter chain omega 3 fatty acids. The mass and specific activity of longer chain omega 3 fatty acids remained constant. 5. There was an accumulation of 14C activity and C22:6 omega 3 in PE at the expense of PC. 6. The pattern of incorporation of 32P inorganic phosphate into molecular classes of phosphatidylcholine (PC) of EFA deficient fish indicated that the rate of turnover of docosahexaenoyl PC was not diminished by EFA deficiency. 7. It is hypothesized that retention of C22:6 omega 3 in EFA deficiency is due to the presence of an efficient recycling system during membrane turnover.