Algal addition in sea bass (Dicentrarchus labrax) larvae rearing: effect on digestive enzymes

Two groups of Dicentrarchus labrax were reared from day 5 to day 20 post-hatching with live prey in running seawater with or without algae. The concentration of algae Isochryisis galbana was maintained between 20 000 to 40 000 cells ml(-1). On day 20, each group was divided into two subgroups, one still receiving live prey, the other fed a compound diet until day 32. On day 32, larvae fed live prey in the presence of algae exhibited an 18% higher survival than larvae reared without algae; in group fed compound diet, the algae supply induced a 26% survival enhancement. At day 16, it was observed a 40% weight improvement in the group reared in the presence of algae compared to the group reared without algae. At day 32, a slight but significant positive effect of algae on larvae weight was still noted in the group fed compound diet. From day 8 to day 16, the presence of algae in the rearing water resulted in an increase in trypsin activity whereas amylase and chymotrypsin were not affected. At day 26, alkaline phosphatase and maltase assayed in purified brush border membranes of intestine were significantly higher in larvae reared in seawater with algae than in those reared in clear water. This result suggests that the presence of algae facilitates the onset of hydrolytic functions of cell membranes. The significant improvement in survival of larvae reared in the presence of algae was related to the early development of brush border membranes. It is concluded that the algae acts by triggering digestive enzyme production, at both the pancreatic and intestinal level. (C) 1998 Elsevier Science B.V.