IMPROVEMENT OF THE NUTRITIONAL-VALUE OF ROTIFERS BY VARYING THE TYPE AND CONCENTRATION OF OIL AND THE ENRICHMENT PERIOD

Several enrichment conditions (type and concentration of oil in cultur e medium and time of enrichment) were tested in order to study their i nfluence on rotifer (Brachionus plicatilis) lipid and fatty acid compo sition as well as on its population profile. Rotifers pre-fed on baker 's yeast (Saccharomyces cerevisiae) were enriched with lipid emulsions containing triacylglycerols (TAG) or methyl ester (ME) mixtures at th ree different concentrations. Rotifers were sampled after 0 (yeast-fed rotifer), 3, 6, 12 and 24h enrichment. At every concentration and tim e assayed, the highest lipid levels were obtained when using TAG. In s pite of the differences existing in saturated and monounsaturated fatt y acid composition between the enrichment emulsions, rotifers tended t o maintain the level of these fatty acids independently of the enrichm ent period and oil concentration. Increasing the enrichment period rat her than the amount of oil present in the medium was found to be more efficient in increasing the n - 3 highly unsaturated fatty acids (n - 3 HUFA) level in rotifers. Rotifers reflected a better incorporation o f eicosapentaenoic acid (EPA, 20:5n - 3) than of docosahexaenoic acid (DHA, 22:6n - 3), regardless of the ratio between both fatty acids in the emulsions. The use of ME as an enrichment source produced greater mortality in egg-carrying females than when using TAG.