Optimising the essential fatty acids in the diet for weight gain of the prawn, Penaeus monodon

Abstract

A study of the influence of the proportion of dietary essential fatty acids (EFA) in the lipid of diets fed to the prawn, Penaeus monodon, showed clearly that these nutrients are required as a proportion of the total fatty acids in the diet. A factorial array of diets were prepared to contain optimal levels (g kg −1) of the fatty acids, linoleic (LOA, 18:2 n−6), linolenic (LNA, 18:3 n−3), eicosapentaenoic (EPA, 20:5 n−2) and docosahexaenoic (DHA, 22:6 n−3). As a second factor to the study, the total amount of lipid in the diet was also increased at incremented levels from 45 to 135 g kg −1 at 30 g kg −1 increments. The weight gain of prawns was greatest (156.2±6.2%) when their diet contained 75 g lipid kg −1, of which 30 g kg −1 was essential fatty acids. Weight gain of prawns fed with diets containing 45 g lipid kg −1 with 17 g of essential fatty acids kg −1 was greater (148.0±3.4%) than prawns fed with the diet that had 45 g lipid kg −1 and 30 g of essential fatty acids kg −1 (124.0±6.8%). The nutritional condition of the prawns, as determined by the amount of lipid in their digestive glands, was generally reflective of weight gain, though there were exceptions, with higher lipid levels in prawn DG from faster growing prawns. The fatty acid composition of the DG lipid generally mimicked that of the dietary lipid. The proportions of each of the essential fatty acids in the DG lipid varied marginally between treatments, but generally LOA, LNA, EPA and DHA levels in the DG fatty acids were present in slightly lower proportions than that in the diet. The amount of dietary lipid present influenced the composition of the fatty acids in the DG lipid when the lowest inclusion level of lipid was compared with the higher inclusion levels. The results of this study clearly indicate that EFA are required as a proportion of the total fatty acids in the diet, and not as a proportion of the diet. Accordingly, it is suggested that EFA should be defined as a percentage of the total fatty acids in conjunction with an indication of the amount of lipid in the diet. This study also showed that for weight gain, the optimal total lipid level of the diet is less than 105 g kg −1.