In this study, we have evaluated the incorporation of two types of protein hydrolysates at 9 and 12% levels of inclusion, one from yeast (Saccharomyces cerevisiae, YPH) and another one from pig blood (PBPH), in microdiets for gilthead sea bream (Sparus aurora) larvae, and compared these results to a microdiet containing fish protein hydrolysate and another group only fed with enriched live prey (rotifers and Artemia). The trial consisted in substituting up to 75% (wt/wt) the enriched Artemia with the experimental microdiets from 15 to 40 days post-hatch, whereas larvae were exclusively fed on microdiets from 40 to 55 dph. Protein hydrolysates used in the present study were obtained from different raw materials (yeast, pig blood and fish protein concentrate) and differed in their amino acid (AA) profile and in their molecular weight distribution. YPH and PBPH were mainly composed by free amino acids (FAA) (44%, MW<200 Da), di- and tripeptides (50%, 200