The enrichment and retention of ascorbic acid in rotifers fed microalgal diets

The enrichment and retention of ascorbic acid (AA) was investigated in rotifers Brachionus plicatilis fed on microalgae (Nannochloropsis oculata and Isochrysis sp. (T.ISO)) and baker's yeast Saccharomyces cerevisiae. The concentrations of AA of the rotifer diets used in the study differed significantly: 4200 mu g g(-1) of dry weight in Isochrysis sp. (T.ISO), 2600 mu g g(-1) in N. oculata and only 77 mu g g(-1) in S. cerevisiae. Rotifers contained 620 mu g AA g(-1) prior to the experimental feeding. When subsequently fed for 3 h on microalgae at a ration of 0.13 mg dry microalgae per 10(6) rotifers rapidly and efficiently increased their content of AA: Isochrysis sp.-fed rotifers contained 1600 mu g AA g(-1) and N. oculata-fed rotifers contained 1100 mu g AA g(-1). Concentrations were boosted by a further feeding of a second ration of algae at three times the initial feeding ration; 21 h later, Isochrysis sp.-fed rotifers contained 2500 mu g AA g(-1) and N. oculata-fed rotifers contained 1700 mu g AA g(-1). This represented a 180% and 310% increase in the pre-feeding vitamin concentrations in Isochrysis sp. and N. oculata-fed rotifers, respectively. There were no significant changes in AA concentration in rotifers fed a similar ration of yeast throughout the feeding period (520-620 mu g AA g(-1)). Rotifers retained AA during a subsequent 24 h non-feeding period, with no significant changes in the concentrations in any of the rotifer groups. The production of rotifers rich in AA may be particularly valuable for the culture of fish larvae that have a high requirement for the vitamin.