Nutritional effects of algal addition in first-feeding of turbot ( Scophthalmus maximus L.) larvae

The effect which microalgal addition and rotifer enrichment with algae had on survival, growth rate and fry viability during first-feeding were examined for turbot ( Scophthalmus maximus L.). Addition of the microalgae Isochrysis galbana or Tetraselmis sp. together with rotifers Brachionus plicatilis, grown on yeast and oil emulsion, and Artemia greatly improved rearing success, whereas short-term enrichment of the rotifers with Tetraselmis sp. gave only improved viability. The algae modified the relative fatty acid composition of rotifers. Rotifers with I. galbana exhibited and increased level of 22:6 n-3 and a lower level of 20:5 n-3, whereas the opposite change occurred when Tetraselmis sp. was used. Addition of either of the two algal species at 1 mg cl −1 to the larval tanks resulted in a constant lipid level and high egg ratio of the rotifers, and thereby also high individual biomass content. Without algal addition, the lipid content of the rotifers decreased by 20% day −1 in the early phase, and their egg ratio became close to zero. In addition to improved nutritional conditions of the larvae, some other factor, e.g. some trigger mechanism or changed microbial or light conditions, also can operate to explain the increased early appetite of larvae with microalgae added and must be taken into consideration.