THE ESSENTIAL FATTY-ACID REQUIREMENT OF MILKFISH (CHANOS-CHANOS FORSSKAL)

The essential fatty acid (EFA) requirement of milkfish was examined by a 12-week feeding trial using defined, purified diets at water temperature of 28-29-degrees-C and salinity of 32 parts per thousand. The test diets contained varying levels of 18:0 (triglyceride form, TG), 18:3(n-3), 18:2(n-6) and (n-3) highly unsaturated fatty acids (n-3 HUFA). Milkfish juveniles were starved for 7 days and were than fed lipid-free diet for 30 days before the initiation of feeding trials. Low growth and feed efficiency together with high mortalities were observed in fish fed the lipid-free diet as well as in the EFA-deficient diet. Supplementation of 2% 18:2(n-6) to the tristearin based diet did not improve growth rate of milkfish as effectively as feeding with (n-3) fatty acids. The highest weight gain was obtained in milkfish fed a combination of 5% 18:0 + 1.0% 18:3(n-3) + 0.5% 20:5(n-3) + 0.5% 22:6(n-3) although the supplementation of 2% 18:3(n-3) alone or combination of 0.5% 20:5(n-3) + 0.5% 22:6(n-3) to the tristearin based diets were also effective for improvement of growth. Thus, (n-3) fatty acids, such as 18:3(n-3) and (n-3)HUFA were nutritionally more important than 18:2(n-6) for milkfish. The fatty acid composition of the polar lipids from whole body of milkfish juveniles fed the various test diets were influenced by the composition of the dietary fatty acids.