The dietary linoleic and linolenic fatty acids requirements of the prawn Penaeus monodon

The dietary requirement of the prawn Penaeus monodon for linoleic (LOA) and linolenic (LNA) fatty acids was examined in the absence of other long-chain polyunsaturated and highly unsaturated fatty acids (PUFA-20:2, 20:3, 22:2, 22:3 and HUFA-18:4, 20:4, 20:5, 22:4, 22:5, 22:6, respectively). Incremented dietary amounts of LOA (7, 14, 21, 28 and 35% of total fatty acids) and LNA (0, 7, 14, 21 and 28% of total fatty acids) were examined in a 5 x 5 factorial growth experiment lasting 50 days. An additional diet containing both PUFA and HUFA (cod-liver oil) was provided as a reference. The total lipid content (excluding sterols) of each of the 26 diets was maintained at 70 g kg(-1) of dry diet. The fatty acid composition of the neutral lipid was manipulated by blending different plant oils and supplementing with purified free fatty acids to provide the desired fatty acid composition upon addition to the total diet. At the end of the 50-day growth experiment, the prawn digestive gland (DG) was quantitatively analysed for lipid and fatty acid content. Prawns fed the reference diet increased in weight (mean +/- SEM) by 214 +/- 6%. Growth was generally greater when combinations of LOA and LNA were used. The best growth (213 +/- 17%) was obtained with the diet containing a fatty acid content of 14% LOA and 21% LNA. This growth was comparable to that of the reference diet. The digestibility of the total lipid in the diet was usually higher when both fatty acids were present. The lipid content of the DG was highest in prawns fed diets containing both LOA and LNA, similar to the growth response. The fatty acid composition of the prawn's DG lipid reflected the fatty acid composition of the diet. However, the maximum assimilation of LNA in the DG lipid (14.2% of DG lipid fatty acids) was about half that of LOA (32.5% of DG lipid fatty acids).