NUTRITIONAL EFFECTS OF ALGAL ADDITION IN 1ST 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 w ere examined for turbot (Scophthalmus maximus L.). Addition of the mic roalgae Isochrysis galbana or Tetraselmis sp. together with rotifers B rachionus plicatilis, grown on yeast and oil emulsion, and Artemia gre atly improved rearing success, whereas short-term enrichment of the ro tifers with Tetraselmis sp. gave only improved viability. The algae mo dified the relative fatty acid composition of rotifers. Rotifers with I. galbana exhibited an increased level of 22:6n-3 and a lower level o f 20:5n-3, whereas the opposite change occurred when Tetraselmis sp. w as used. Addition of either of the two algal species at 1 mg Cl-1 to t he larval tanks resulted in a constant lipid level and high egg ratio of the rotifers, and thereby also high individual biomass content. Wit hout 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 oth er factor, e.g. some trigger mechanism or changed microbial or light c onditions, also can operate to explain the increased early appetite of larvae with microalgae added and must be taken into consideration.