NUTRITIONAL COMPOSITION OF ROTIFERS FOLLOWING A CHANGE IN DIET FROM YEAST AND EMULSIFIED OIL TO MICROALGAE

Rotifers, Brachionus plicatilis, fed baker's yeast and a lipid emulsio n (High DNA Super Selco, INVE Aquaculture NV Systems SA, Belgium), wer e harvested and fed Isochrysis galbana for 72 h, the nutrient composit ion was analysed during this period. The enrichment effect on the roti fers following transfer to I. galbana was most pronounced for ascorbic acid and thiamin. I. galbana seemed to contribute very little as a so urce of the lipid-soluble vitamins. Most of the minerals and trace ele ments were unaffected by the transfer to I. galbana, but Fe, Mn, As an d Cd increased, Cu and Ni decreased whereas the effect on Cr and Mo we re uncertain. The fatty acid composition of the rotifers changed towar ds the composition of I. galbana during the experimental period. Inter mediate glycogen levels were measured in the rotifers at all sampling times. With the exception of lysine, serine and proline, all amino aci d levels seemed to be unaffected by the transfer to I. galbana. This s tudy showed that transfer of rotifers to microalgae (I. galbana) feedi ng had a positive effect on nutritional value. Macronutrients were mai ntained at adequate levels, and algal feeding improved the nutritional quality of rotifers with respect to water-soluble vitamins. Changes i n rotifer nutrient composition are discussed in relation to nutritiona l requirements of fish larvae.