The maturation of the digestive functions in sea bass (Dicentrarchus labrax) larvae was evaluated by the enzymatic profile of pancreas and intestine brush border membranes. Sea bass larvae were weaned at day 25 with three simplified diets different by their protein nature: 100% fish meal (FP), 100% casein mixture (CP) and 50% fish meal-50% casein mixture (CFP). The casein mixture contained 35% of hydrolysate. The control group was fed live preys. The specific activity of amylase decreased with age irrespectively of the diets whereas the specific activity of trypsin was enhanced. The casein mixture reduced pancreatic secretion in amylase and trypsin. The CFP group differed from the other groups fed on compound diets, exhibiting as soon as day 32 high activities of brush border enzymes, similar to controls. This sharp increase between day 25 and 32 appeared to be crucial for larval survival. The addition of a protein hydrolysate in a weaning diet seems to facilitate this maturation process.

Sea bass (Dicentrarchus labrax) larvae were weaned at day 25 with microparticulated diets in which 10% of the nitrogen supply had different molecular forms: amino acid mixture (SLAA), casein hydrolysate (SLH) or fish meal (SLP). The control group (LP) was fed live prey. No difference was observed in larval growth between the weaned groups, but the survival was significantly higher in the SLH group. Trypsin secretion was stimulated in the SLAA group, whereas the SLH diet reduced the secretion from the exocrine pancreas. The activity of the leucine-alanine peptidase, located in the cytosol of enterocytes, remained high in all weaned groups. However, the activity of the peptidases of the brush border membrane increased during the development phase in the control group. These results suggest that weaning with a classic compound diet delays enterocyte differentiation by maintaining the larval features of digestion. A compound diet containing protein hydrolysate can attenuate the delay of intestinal maturation.

Variations in some enzyme activities during larval development of sea bass fed live prey were investigated from hatching to day 40. Fluctuations in the enzyme specific activities (except for trypsin) occurred in three phases: initially a sharp increase until day 12, followed by a plateau and subsequently a decrease around day 23. Then activities remained constant until day 40. Trypsin activity kept rising until day 23, then fell. Enzymatic adaptation to a change in diet was studied by feeding larvae with microparticulate diet from day 25. Adaptation to dietary change was observed for amylase, alkaline phosphatase and leucine aminopeptidase, assayed in whole larvae. In larvae fed microparticulate dry diet, the activities of these three enzymes tended to be higher than in those fed natural prey. Although poor growth was observed in larvae fed microparticles, the brush border enzyme activities purified from whole body homogenate, were not impaired.