The effect of lipid supplementation on growth and fatty acid composition of Tapes philippinarum spat

The present study investigated the possible use of emulsions as;an artificial lipid supplement to live algae for seed of the Manila clam Tapes philippinarum. The uptake and assimilation of an emulsion, rich in docosahexaenoic acid (DHA, 22:6n - 3) and eicosapentaenoic acid (EPA, 20:5n - 3) and fed at concentrations of 20 and 40% of the algal dry weight, were verified analytically by fatty acid analysis of the animals and their diets. Dietary requirements for n - 3 highly unsaturated fatty acids (HUFA) were examined by supplementing Dunaliella tertiolecta, which contains no polyunsaturated fatty acids longer than 18:3n - 3 and Tetraselmis suecica, which contains EPA but only trace amounts of DHA. An algal mixture of Isochiysis galbana (clone T-Iso) and Chaetoceros neogracile(l:l, on dry weight basis) was used as the control diet. After 4 weeks, the lipid supplementation resulted in a significant increase of the DHA level in the seed compared to the animals fed non-supplemented Dunaliella (from 9.5 to 19.8 and 22.0% at a supplementation of 20 and 40%, respectively) or Tetraselmis (from 3.4 to 24.8 and 26.9%, at a supplementation of 20 and 40%, respectively) diet.Feeding solely D. tertiolecta resulted in a significantly lower daily growth rate (DGR) compared to animals fed T. suecica or the mixed algal diet. Lipid supplementation improved the DGR of the clams fed D. tertiolecta while hardly any effect could be detected in those fed T, suecica.The poor nutritional value of D. tertiolecta was indicated by the continuous decrease of the DGR and resulted in a DGR I:hat was no longer significantly different from the starved ones at the end of the experiment. (C) 1998 Elsevier Science B.V. All rights reserved.