PARTIAL SUBSTITUTION OF DIPEPTIDES AND TRIPEPTIDES FOR NATIVE PROTEINS IN SEA BASS DIET IMPROVES DICENTRARCHUS-LABRAX LARVAL DEVELOPMENT

To determine whether incorporation of peptides into diets can improve larval development, sea bass (Dicentrarchus labrax) larvae were fed fo r 21 d one of three isonitrogenous, isoenergetic semipurified diets in which enzymatic hydrolysate (75% di- and tripeptides) of fish meal pr oteins was substituted for 0, 20 or 40% of native fish meal proteins. Growth and survival were significantly greater (P < 0.05) in larvae fe d peptide diets compared to those fed only native protein, with the be st performance exhibited by those fed the 20% level of peptides. Chymo trypsin activity was much higher in groups fed peptide diets compared to that fed all native protein (P < 0.001), indicating a greater prote olytic capacity of the pancreas. At the intestinal level, activities o f the brush border enzymes, aminopeptidase, maltase and gamma-glutamyl transpeptidase, increased with age while the cytosolic enzyme, leu-al a peptidase, decreased with age (P < 0.001). These changes in enzymati c activities correspond to the normal development of intestinal digest ion. This development occurred earlier in the group fed 20% peptide-su bstituted diet than in the two other groups. The better larval perform ances observed in groups fed diets containing peptides can be related to the enhanced proteolytic capacity of the pancreas and the earlier d evelopment of intestinal digestion.