Abstract: Using the 15N stable isotope technique, nitrogen (N) assimilation of Artemia was determined in feeding regimes where the two yeast strains wild-type (WT) and its mutant mnn9 were gradually replaced by HT3 or HT6, or where the bacterial strains were gradually replaced by each yeast strain. A trypsin assay was performed on Artemia fed the various replacement feeding regimes, in order to detect the effect of the presence of bacteria or of the yeasts on the protein digestive response in Artemia. HT6 fed Artemia showed a higher N assimilation than when using HT3, suggesting a better food value of HT6 for Artemia.