Optimizing the essential fatty acids, eicosapentaenoic and decosahexaenoic acid, in the diet of the prawn, Penaeus monodon

The dietary requirements of Penaeus monodon for eicosapentaenoic (20:5n-3; EPA) and docosahexaenoic (22:6n-3; DHA) acids were examined. These requirements were examined when dietary levels of linoleic (18:2n-6; LOA) and linolenic acids (18:3n-3; LNA) were also provided at previously established optimal levels of 14 and 21% respectively of the total lipid fatty acids. A 5 x 5 factorial design was used with incremental amounts (0, 4, 8, 12 and 16% of total fatty acids) of EPA and/or DHA. An additional diet containing cod-liver oil was provided as a reference diet. The total lipid content of all of the 25 treatments and reference diets was maintained at the same level of 75 g kg(-1). Growth of prawns fed with the reference diet after 50 days was 244 +/- 21%. The greatest response to singular additions of EPA or DHA was with a 12% inclusion of either fatty acid, resulting in 287 +/- 21 and 293 +/- 18% weight gain, respectively. Growth was generally better when combinations of EPA and DHA were used, the optimal combination being EPA 4% and DHA 4%, resulting in 335 +/- 25% weight gain. Addition of high levels of either of the highly unsaturated fatty acids (HUFA) in the diet had a negative effect on growth. Digestibilities of the total neutral lipid and specific fatty acids were examined during the growth trials. The digestibility of total neutral lipid was usually higher when either or both HUFA were present, however there were few significant differences between treatments that contained either or both HUFA. Following the growth trials, digestive glands (DG) of prawns fed with the various diets were analysed to determine the total lipid content and fatty acid composition. Total lipid in the digestive gland increased with the inclusion of DHA, but was not significantly affected by the addition of EPA. The fatty acid composition of the digestive gland lipid generally reflected that of the diet. However, the maximum retention of EPA (11.1% of total DG fatty acids) and DHA (10.7% of total DG fatty acids), was not directly proportional to the amount of either fatty acid present in the diet. These results demonstrate that both EPA and DHA have considerable growth promoting capacity. This growth promoting capacity is enhanced when an optical balance of both fatty acids are incorporated into the diet.