Optimising the essential
fatty acids in the diet for weight gain of the prawn, Penaeus monodon
B.D. Glencross, D.M. Smith, M.R. Thomas, K.C.
Williams-2002
Aquaculture, 204(1-2): 85-99
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) of the fatty acids, linoleic
(LOA, 18:2n-6), linolenic (LNA, 18:3n-3), eicosapentaenoic
(EPA, 20:5n-2) and docosahexaenoic (DHA, 22:6n-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 at 30 g/kg increments.
The weight gain of prawns was greatest (156.2±6.2%) when their diet
contained 75 g lipid/kg, of which 30 g/kg was essential fatty acids. Weight
gain of prawns fed with diets containing 45 g lipid/kg with 17 g of
essential fatty acids/kg was greater (148.0±3.4%) than prawns fed with the
diet that had 45 g lipid/kg and 30 g of essential fatty acids/kg (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.
(Department of Zoology, The University of Queensland,
St Lucia 4072, Queensland, Australia, Tel.: +61-8-9239-8103, fax:
+61-8-9239-8105, e-mail: bglencross@fish.wa.gov.au)