Essential fatty acid requirements and related aspects of lipid metabolism in the red drum, S̲c̲i̲a̲e̲n̲o̲p̲s̲ o̲c̲e̲l̲l̲a̲t̲u̲s̲

Abstract

Lipid is a vital macronutrient that provides energy and fatty acids which mediate important biochemical processes. Lack of information on the specific essential fatty acid (EFA) requirements of red drum, as well as their responses to different types of dietary lipid has limited the development of an optimized feed for this species. Therefore, two separate feeding experiments and laboratory analyses were conducted to establish the EFA requirements of juvenile red drum. Fish were fed semipurified diets containing 7% total lipid consisting of different combinations of tristearin (18:0) and ethyl esters of n-9, n-6 and n-3 family fatty acids, including a mixture of highly unsaturated fatty acids (HUFA) containing predominantly eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). EFA-deficient diets (tristearin and oleate) rapidly reduced fish growth, survival and feed efficiency. Fish fed tristearin also showed fin erosion and exhibited a "shock syndrome." Elevated liver lipid, increased monoenes, and conservation of n-3 HUFA in polar lipids were other EFA-deficiency signs. Results indicated that 0.5% n-3 HUFA satisfied the EFA requirement of red drum, which is similar to that of other marine carnivorous fishes. However, 2.5% dietary HUFA in a diet containing 7% total lipid strongly suppressed weight gain. Utilization of different triglycerides by red drum was examined using diets containing 7% lipid consisting of tristearin, triolein, linseed oil, or menhaden oil, sources rich in 18:0, 18:1n-9, 18:3n-3 and n-3 HUFA, respectively. Growth was influenced by dietary fatty acids, with progressive increase in weight gain of fish fed linseed oil and menhaden oil. However, survival, feed efficiency and appearance of fish were improved by triglycerides in comparison with ethyl esters of fatty acids used previously. Finally, the quantitative EFA requirements of red drum in relation to total dietary lipid were assessed using diets containing 7 or 14% total lipid as menhaden oil, or linseed oil with or without supplemental n-3 HUFA. Quantitative EFA requirements increased with dietary lipid, and growth was best in fish fed 20:5n-3 plus 22:6n-3 at 10.7% of dietary lipid. Practical diets for red drum should include lipids containing predominantly n-3 fatty acids, including sufficient HUFA to meet EFA requirements.