Evaluation of different types and levels of triglycerides, singly and in combination with different levels of n−3 highly unsaturated fatty acid ethyl esters in diets of juvenile red drum, Sciaenops ocellatus

Abstract

Two separate feeding trials were conducted to assess different aspects of lipid nutrition of juvenile red drum. In the first 8-week trial, growth, survival, feed efficiency, total lipid and fatty acid composition of whole-body, muscle and liver tissues were used to establish the nutritional efficacy of different triglycerides for this species. Semipurified diets contained 7% total lipid from tristearin, triolein, linseed oil or menhaden fish oil, sources rich in 18:0, 18:1, 18:3 n−3 and n−3 highly unsaturated fatty acids (HUFA), respectively. Fish were maintained in a recirculating system containing brackish water (5 ± 2 ppt) with a temperature of 25 ± 2°C. Growth was influenced by dietary lipid, with progressive increases in weight gain of fish fed linseed oil and menhaden oil. The latter contains substantial amounts of the n−3 HUFA that are necessary to satisfy the essential fatty acid (EFA) requirements of this species. Elevated monoenes were present in tissue lipids of fish fed tristearin and triolein, and n−3 HUFA were conserved in the polar lipid fractions. The second 6-week feeding trial was conducted to assess the quantitative EFA requirements of red drum in relation to total dietary lipid. Diets contained 7 or 14% total lipid from menhaden oil, or linseed oil with or without supplemental n−3 HUFA in the form of ethyl esters. Quantitative EFA requirements increased with dietary lipid, and growth was best in fish fed 20:5 n−3 plus 22:6 n−3 at 10% of dietary lipid.