Peptide molecular weight, distribution of soluble protein fraction affects growth performance and quality in European sea bass (Dicentracrchus labrax) larvae

Dicentrarchus labrax were fed from 10 to 40days posthatching with six microdiets differing in the inclusion level (60gkg(-1) and 120gkg(-1)) and type of protein hydrolysate (PH; yeast, YPH; pig blood, PBPH; pig red blood cells, PRBCPH). A microdiet containing 120gkg(-1) fish PH (FPH) was used as a control. PH differed in their amino acid (AA) profile and molecular weight distribution and therefore the tested microdiets too. The estimated content in FAA and di- and tripeptides in the FPH microdiet was 2gkg(-1) and 44gkg(-1), respectively. FAA estimated levels in YPH and PBPH microdiets were 26gkg(-1) and 53gkg(-1), whereas levels of di- and tripeptides were 30gkg(-1) and 60gkg(-1), respectively. The estimated levels of FAA in PRBCPH microdiets were 8gkg(-1) and 17gkg(-1), whereas estimated levels of di- and tripeptides were 11gkg(-1) and 22gkg(-1), respectively. Results revealed that FPH may be replaced by alternative PH from yeast and pig blood products, as fish fed those diets performed, in terms of growth, survival, digestive function and incidence of skeletal deformities, as well as those fed the FPH microdiet. Using YPH, PBPH and PRBCPH, the inclusion level of PH in microdiets might be reduced to a half with respect to current practices using FPH.